ST 2272 (WOL) (13-6-2008)

ST 2272 (WOL) (13-6-2008) Satellite Communication Operating Manual Ver 1.1 Satellite Communication Trainer Table of Contents 1. Introduction 4 2. Features 4 3. Technical Specifications 5 4. Satellite Communication 6 5. Types of Satellites 10 , Passive Satellites , Active Satellites , Non synchronous Satellites , Geo synchronous Satellites 6. Special Purpose Communication Satellites 11 , Direct Broadcast Satellite system , M - SAT , V - SAT , RADARSAT 7. Modulation Techniques for Satellite Links 14 8. Satellite Applications 15 , Satellite Communication Applications , Remote Sensing and Path Observation Application , Meteorological Application , Military Applications , Scientific and Technological Applications 9. Microwave Communication 16 10. General Structure of Satellite Communication System 19 11. Orbital Aspects of Satellite Communication 24 12. Satellite Sub Systems 26 13. Satellite Link Design 29 14. Basic Receiving System 34 15. Understanding Basic Concepts of Satellite Communication 37 16. Glossary of Satellite Communication Terms 45 2 17. Experiments , Experiment 1 64 Understanding Basic concepts of Satellite communication. , Experiment 2 72 Establishing a Direct Communication Link between Uplink Transmitter and Down link Receiver using Tone Signal , Experiment 3 73 Setting up an Active Satellite Link and demonstrate Link Fail Operations , Experiment 4 75 Establishing an Audio-Video Satellite Link between Transmitter and Receiver , Experiment 5 77 Communicating „Voice? Signal through Satellite Link , Experiment 6 79 Changing different combinations of Uplink and Downlink Frequencies and to check the Communication Link , Experiment 7 81 Transmitting & receiving three separate Signals (Audio, Video, Tone) simultaneously through satellite link , Experiment 8 83 Transmitting & receiving Function Generator Waveforms through Satellite Link , Experiment 9 85 Transmitting & receiving PC Data through Satellite Link 18. List of Accessories 87 3 Introduction Satellite Communication Trainer provides an in-depth study of basic Satellite communication system. It consists of Uplink Transmitter, Satellite Link and a Downlink Receiver, which can be conveniently placed in the laboratory. The Satellite can be placed at an elevated position if needed. The Satellite Transponder receives signal from Uplink Transmitter and retransmits at different frequencies to a Downlink Receiver. The Uplink and Downlink frequencies are selectable and can carry three signals - Video, Audio, Voice, and Data simultaneously. Any Broadband signal or Digital/Analog data or Function Generator waveforms may be communicated through the Satellite link. The students can conduct large number of experiments on this Trainer. The Operating manual illustrates basic theory and glossary of satellite communication terms along with experiments. Features , Simultaneous communication of three different signals at each up-linking frequency. , 2414 - 2468 MHz PLL microwave operation. , Crystal Control Frequencies. , Communicate Audio, Video, Digital data, PC data, Tone, Voice, function generator waveforms etc. , Communication of external broad band digital and analog data and base band signals , Choice of different transmitting and receiving frequencies. , Built-in microphone and speaker for Voice and Audio link. , Detachable Dish Antenna at each station. , Facility to attach Analog/ Digital Communication Kits. 4 Technical Specifications Uplink Transmitter : , Transmit three signals simultaneously at each up-linking frequency , 2450-2468 MHz up-linking frequencies selectable by Frequency selection switch and LED indication. , 4 MHz clock frequency. , Wide band RF amplifier. No manual matching required. , PIC16F84 - 8 Bit RISC processor based PLL. , 16 MHz Bandwidth , Frequency select switch and LED indication. , FM Modulation of Audio and Video. , 5/5.5 MHz Audio and 8 MHz Video Modulation. , Detachable Dish Antenna. , Radiated Power output 25mW (approximately) with power control. , Transmit Audio, Video, Digital/Analog data, PC data, Tone, Voice, function generator waveforms etc. , Separate terminals provided for different inputs. , Power Supply : 230 Volts , 10%; 50Hz. Satellite Link : , Transponder with selectable frequency conversion. , Choice of 2 downlink frequencies 2414-2432 MHz. , Rotary Switch for selecting Uplink frequency. , Link Fail operation. , Detachable Dish Antennas. , Radiated power 25mW (approx.) with Variable gain control. , Power Supply 230 Volts, , 10%, 50 Hz. Downlink Receiver : , Receives and demodulate three signals simultaneously. , Intermediate Frequency 479.6 MHz (approximately). , 2414-2432 MHz fix frequency tuning. , -60 dBm sensitivity at tuner input , Built in speaker for audio and video output. , Detachable Dish Antenna. , Power Supply : 230 Volts ,10 %; 50Hz. 5 Satellite Communication General Aspects : Satellite communication is one of our most rapidly growing and evolving technologies bringing with it a multitude of business opportunities in the decades to come. A communications Satellite is a spacecraft that carries aboard communications equipment, enabling a communications link to be established between distant points. An all embracing definition of a spacecraft would include deep-space probes such as the Voyager series, but here only those Satellites that orbit the earth will be considered. Satellites that orbit the earth do so as a result of the balance between centrifugal and gravitational forces. Johannes Kepler (1571-1630) discovered the laws that govern Satellite motion. Although Kepler was investigating the motion of planets and their moons (so-called heavenly bodies), the same laws apply to the artificial Satellites launched for communication purposes. Before examining the role these Satellites play in telecommunications, we should know the Kepler's laws as they apply to such Satellites. Kepler's laws apply to any two bodies in space that interact through gravitation. The more massive of the bodies is called the primary and the other the secondary or Satellite. The entire Text given in this chapter is collected and compiled from various sources and is basically to impart some basic knowledge to the students, this is purely theoretical and no concern with the classroom trainer design. Classroom trainer is to show the functioning of satellite communication by using the blocks. A communications Satellite is essentially a microwave link repeater. It receive the energy beamed up at it by an earth station and amplifies and returns it to earth at a frequency of about 2 gigahertz away; this prevents interference between the uplink and the downlink. Communication Satellites appear to hover over given spots above the equator. This does not make them stationary, but rather geostationary. That is to say, they have the same angular velocity as the Earth (i.e., one complete cycle per 24 hours), and so they appear to be stationed over one spot on the globe. Celestial mechanics shows that a Satellite orbiting the earth will do so at a velocity that depends on its distance from the earth, and on whether the Satellite is in a circular or an elliptical orbit. For example, a Satellite in a low circular orbit, as was Sputnik 1, will orbit the earth in 90 minutes. The moon, which is nearly 385,000 Km away, orbits in 28 days. A Satellite in circular orbit 35,800 Km away from the earth will complete a revolution in 24 hours, as does the earth, and this is why it appears stationary. 6 Figure 1 General Structure of Satellite Communication System : Satellites are always stationed in round or elliptical orbit. Elliptical orbits are not good because the speed gets varied. There are mainly two types of dish antenna on the Satellite, one for receiving and one for transmitting the signal. These Satellites are basically repeater stations. These Satellites are stationed at a specific angle & direction from the earth. The speed of the Satellite is same as that of earth. These Satellites are also known as Geosynchronous Satellites. The concepts underlying Satellite broadcasting, first stated in Arthur C. Clarke's groundbreaking article in the October 1945 edition of Wireless World, are rather simple. Signals are beamed into space by an "uplink" antenna, received by an orbiting Satellite, electronically processed, broadcast back to earth by a "downlink" antenna and received by an earth station located anywhere in the Satellite's footprint". Most communication Satellites are parked in the "Clarke Belt" or the "geo synchronous" arc at 22,247 miles directly above the equator. This circle around the earth is unique because in this orbit the velocity of Satellites matches that of the surface of the earth below. Each Satellite thus appears to be in a fixed orbital position in the sky. This allows a stationary antenna to be permanently aimed towards any chosen geo synchronous Satellite. The Satellite communication system must generally meet all requirements that apply to radio communications. In the United States, for example, the Federal Communications Commission (FCC) mandates these standards. These include power output, frequency and bandwidth allocations, types of transmission (digital or analog) as well as polarization and modulation methods. A brief introduction to microwaves and communication fundamentals is presented next to explain some of these concepts. The same principles underlie all forms of man-made communications. First, information such as voice, data or music is changed into electronic form. The process of transforming this information into an electrical signal is known as coding. The signal is 7 then added or modulated onto a carrier waveform having an assigned frequency. This modulated signal is relayed within an assigned bandwidth at a predetermined power by a transmitter. The carrier wave can be polarized into a variety of forms to allow the assigned frequencies to be used to their fullest extent. When the signal is received, it is usually amplified, extracted from the carrier by a process called demodulation, and filtered to remove noise. This reconstructed form of the original signal is then processed into audio, video or data as required. As we know that Satellite is about 35000 Km. away from the earth. Therefore to transmit the signal to the Satellite & then to retransmit to earth needs high frequency to be used. Practically, it was found that for this purpose frequency range required was 3 to 12 GHz. This frequency range belongs to SHF band. The dish antenna on the Satellite can receive the signals up to frequency 18 GHz. From the transmission center based on earth the RF signal are converted to SHF signal & then with the help of dish antenna they are transmitted to Satellite. These signals are received by the Satellite & after amplification sent back to the earth. The main difference between TV transmission center & Satellite transmission center is that general transmitter transmits its signals in VHF/ UHF range & Satellite transmitter uses SHF range Figure 2 This frequency is very much higher than VHF /UHF. TV tuners cannot directly receive these signals. Therefore some extra equipment is needed to receive these. This is known as Satellite Receiver. The high frequency used for transmitting the signal from earth to Satellite & from Satellite to earth is different. The frequency used by the transmitter station is to transmit the signal to Satellite is known as uplink frequency. And to again transmit it to the earth it uses another high frequency, known as downlink frequency. The use of such high frequencies in Satellite transmission is because of the large distance of Satellite from the earth. 8 There are some more reasons as well. They are : 1. For low frequency the receiving antenna on the Satellite is to be made very large, which is not possible. 2. The used frequency should be able to cross the ionosphere. 3. The used frequency should not disturb the used frequencies on earth. In this whole process Satellite plays an important role. Satellite receives the signal transmitted from earth & sends back to earth. The signal coming from the Satellite acts as a input to the Satellite receiver. In Satellite transmission both analog & digital signals can be transmitted. The transmission center on the earth modulates the input signal to a high frequency carrier. Now the modulated signal is amplified by high power amplifier & then transmitted by a high gain antenna. This signal is received by the antenna of the Satellite amplified by specially made low noise amplifier. After amplification the frequency of these signals gets reduced. This process does not affect the carrier signal. This signal after amplification by high power amplifier is transmitted back to the earth. -12At the receiving station the power of the input signal is very low (10 pW to 1 pW ). The signal is received at the earth station with the help of helical antenna also known as dish aerial. This aerial is mounted very carefully so as to receive maximum amount of signal. The signals coming on the dish aerial is focused on a point & then amplified according to our needs by LNB. LNB is a very important part of the dish aerial. LNB is mounted on dish aerial so as to minimize the transmission losses, then these signals are sent to Satellite receiver. In it the required channel is selected & then it is amplified & demodulated & signal gets converted into a frequency which TV can receive. The power for all the purposes on the Satellite is derived from solar energy, it is about 250 W. Two flaps on both the side of the Satellites receive this power. Satellites are the key component in the telecommunication revolution. Our communication system is now greatly improved because any locations within a Satellite's "view" can be linked without the use of expensive cables or line-of-sight relay towers. Furthermore, a communication Satellite operating as a relay in space can serve vast areas of our globe at once. Up linked signals have powers of fractions of a millionth of a Watts when received by geosynchronous Satellites. In the heart of this communication vehicle, typically about the size of a small truck, these signals are amplified many thousands of times, shifted to a lower frequency range and then re-transmitted back to earth. This frequency conversion reduces terrestrial interference at the receiving station below. If this was not the case, some of the up linked signal could be inadvertently detected by receiving stations near uplink sites along with the desired signal. American C-band circuits use an uplink having a 500 MHz bandwidth spanning the range from 5.925 to 6.425 GHz and the same bandwidth shifted to the lower range of 3.7 to 4.2 GHz for the downlink. (Ku-band relays typically uplink signals from 13.7 to 14.2 Hz and downlink from 11.7 to 12.2 GHz, both ranges also spanning a 500 MHz (bandwidth). 9 Types of Satellites 1. Passive Satellites : Passive Satellites are the Satellites that simply reflect a signal back to earth, there are no gain devices on board to amplify the signal. An advantage being that they do not require sophisticated electronic equipment on board, although they are not necessarily void of power. Some passive Satellite requires a radio beacon transmitter for tracking & ranging purpose. A beacon is a continuously transmitted unmodulated carrier that an earth station can lock onto and use to align its antennas or to determine the exact location of the Satellite. A disadvantage is there in using these due to inefficient use of transmitted power. 2. Active Satellites : Active Satellites are the Satellites that electronically repeat the signal and send it back to earth. It receives, amplifies, and retransmits the signal. The communication capability of active systems with the directional antennas rapidly becomes much greater than that of the passive system as the altitude is increased. 3. Nonsynchronous Satellites : Non-synchronous Satellites are the Satellites that rotate around the earth in a low altitude elliptical or circular pattern. If Satellite is orbiting in the same direction as earths rotation, and at an angular velocity greater than that of earth, orbit is called prograde orbit. If Satellite is orbiting in the opposite direction but at an angular velocity less than that of earth, orbit is called retrograde orbit. Therefore such Satellites are continuously either gaining or falling back on earth and do not remain stationary relative to any particular point on earth. Thus they have to be used when available. Another disadvantage is the need for the complicated and expensive tracking equipments at the earth station. Advantage is that the propulsion rockets are not required onboard the Satellite to keep them in their respective orbit. 4. Geosynchronous Satellites : Geosynchronous Satellites are the Satellites that orbit in a circular pattern with an angular velocity equal to that of earth. They remain at a fixed position with respect to a given point on earth. They are available to all earth stations within their shadow all the time. The shadow of a Satellite includes all earth stations that have a line of sight path to it or lie within the radiation pattern of the Satellite antenna. But they require sophisticated heavy propulsion devices onboard to keep them in a fixed orbit. Orbital time of these Satellites is 24 hrs same as that of earth. 10 Special Purpose Communication Satellites Satellites are not deployed evenly around the orbit but are clustered over regions where services are most in demand. Direct to home broad casting, refer to as direct broad casting Satellites (DBS) services in US, represents one major development in field of Geostationary Satellite. Another is the use of very small aperture terminals (V SAT) for business applications. Third Geostationary Satellite development is mobile Satellite services (MSAT) which extend Geostationary Satellites services into mobile communication for vehicles, ships and aircraft. Rapid development has also been taking place in service using Non-geostationary Satellites. Radarsat is a large polar orbiting Satellite design to provide environmental monitoring services. Possibly most notable development in this area is Global positioning Satellite (GPS) system which has came into every day use for surveying and positioning locations generally. 1. DBS (Direct Broadcast Satellite) System : Direct broadcast satellite system (DBS) also called as broadcast satellite system (BSS) have introduced revolutionary changes into domestic TV series. They provide broadcast transmissions in fullest sense of the word, since the antenna footprints can be made to cover large antennas of the earth. Here reception of TV signals from satellite is direct and is meant for the individual reception and community reception. DBS utilizes high power satellites and regional coverage antennas. Most important feature of DBS is that it allows earth station or terminal to be mounted in domestic area. The universality of reception of DBS system has provided benefits for both the public and programme suppliers. From the public interest standpoint more variety is desirable. For operators point of view, it has given big market with a singular transmission method. Configuration wise a direct broadcasting satellite consists of a television repeater station in Geostationary orbit, a ground station that transmits program signals to the spacecraft, and the consumer terminals that receive the signals from the satellite and convert them to a format compatible with existing TV sets. These system components are derived from existing equipment used for satellite distribution of TV signals to homes, hotels, cable systems and network stations. The DBS systems provide, in addition to TV high fidelity audio, and other services. Some DBS systems also scramble the signals at the program generation facility, thus requiring the descramblers at the consumer terminals. 2. M – SAT : The mobile Satellite (MSAT) system is intended to compliment the existing mobile communications systems such those provided by cellular radio operators, radio common carriers, and telephone companies. This existing mobile service does not adequately cover many rural and remote areas. In the MSAT system the Satellite to mobile link will use L-band frequencies, the down-link frequencies being in range 1550-1559 MHz and the uplink frequencies in the range 11 1626.5-1660.5 MHz. These bands are divided into sub-bands as allocated at the world radio conference (WARC). Communication between Satellite and a fixed station will use frequency in Ku-band. In the base line design presentation in MSAT, each Satellite will employ two large L-band reflector antennas, which will generate nine beams. Frequency reuse in the multiple beam system and frequency sharing and coordination with other user will be required. At least two antenna types are available for use with the mobile unit an omni directional with a gain of 10 dB. Circular polarization will be used to the L-band Satellite - mobile communication and linear polarization for Ku band links. MSAT application : a. Public Safety : Police, Ambulance, Search and Rescue, Fire fight and Emergency relief Operations b. Aeronautical : Operation communication to Commercial Aircraft, Public correspondence, Air traffic control and safety c. Marine : Operation communication to domestic coastal ships, Coast guard operation, Research vessels, Data acquisition, etc. d. Land Application : Constructing projects in remote areas, Resources development, Forestry, Oil, Mining and Transportation etc. 3. VSAT : VSAT stands for very small aperture terminal system. The earth station antenna is typically 2.4 m in diameter. Typically user group includes Banking and Financial Institutes, Airlines and Hotel Booking agencies etc. The structure of the VSAT net work consist of a hub station which provides a broad cast facility all the VSAT in the network, and VSAT themselves which access the Satellite in some form of multiple access mode. The service provider operates the hub station, and it may be shared among the number of users, but of course each user origination has exclusive access to its own access VSAT network. Time division multiplexing is a normal downlink mode on transmission from hub to VSAT, and the transmission can be broadcast for reception by all the VSAT in the network, or address coding can be used to direct message to selected VSATs. 12 4. RADARSAT : Radarsat is Earth resource remote-sensing Satellite. Main applications are : a. Provide application benefits for resource management and maritime safety. b. Shipping and fisheries c. Ocean features mapping d. Oil pollution control and monitoring e. Sea mapping f. Ice berg detection g. Crop monitoring h. Forest management i. Geographical mapping j. Land use mapping etc. RADARSAT is planned to fly in low-earth-near-circular-orbit. Radar Orbital Parameters : Geometry : Circular, sun synchronous (dawn dusk) Altitude (local) : 798 Km Inclination : 98.6 degree Period : 100.7 min Repeat cycle : 24 days Radarsat carries only C- band radar as the sensing mechanism. The rationale for selecting it is that it does penetrate cloud cover, smokes, and haze and it does operate in darkness. Much of sensing is required at high latitudes where solar illumination of the earth can be poor, and where there can be persistent cloud cover. The orbit is described as dawn to dusk. What this means is that the Satellite is in view of the sun for the ascending and descending passages. With the radar sensor it is not necessary to have the earth illuminated under the Satellite; in other words, the sun's rays reach the orbital plane in a broadside fashion. The main operational advantage is that the radar becomes fully dependent on solar power rather than battery power for both the ascending and descending passes. Since there is no operational need to distinguish between the ascending and descending passes, nearly twice as many observations can be made than otherwise would be possible. Further that the solar arrays do not have to rotate, the arrangement leads to a mere stable thermal design for the spacecraft. 13 Radar sat is a comparatively large spacecraft, the total mass in orbit being about 3100 Kg. The radar works at carrier frequency of 5.3 GHz, which can be modulated, with three different pulse widths, depending on resolution requirements. The Satellite completes 14+7/12 revolutions per day. The separations between equatorial crossings are 116.8 Km. In summaries; Radar sat is intended as a rapid response system providing earth imager for a range of operational applications and is intended to complement other earth resources Satellites. Modulation Techniques for Satellite Links To date frequency modulation (FM) is the only form of analog modulation widely used on Satellite links. In exchange for a wide bandwidth and poor spectral efficiency, it offers considerable signal to noise ratio (S/N) improvement. This means that the signal to noise ratio at the output of an FM detector is much larger than the carrier to noise ratio (C/N) at the detector input, provided that the input (C/N) is above a threshold value that is characteristic of that detector. Since the Satellite links have been power limited rather than bandwidth limited and have had to operate with low (C/N) levels, FM has been the analog modulation of choice. As we know that the bandwidth of a frequency modulated waveform with wideband FM is much greater than the bandwidth of the modulating wave form. Hence the bandwidth of the input signal to an FM detector is much greater than the bandwidth of the output signal. The bandwidth compression provided by the detector is accompanied by an improvement in signal to noise ratio provided that the input carrier to noise ratio is sufficiently large. This result is very important to the design and operation of the analog FM Satellite links. The modulation procedures used for terrestrial TV broadcasting and for Satellite transmission are quite different. In terrestrial broadcasting, the audio and video signals are combined and shifted in frequency to an appropriate part of the VHF or UHF band for transmission. The radiated signal is a complex combination of FM (the sound), VSB (the luminance signal), and quadrature DSBSC (the chrominance signal). It occupies a 6 MHz bandwidth. For Satellite transmission the baseband video signal (luminance and chrominance), frequency modulates a video carrier and the two audio signal frequency modulates two audio carriers. The details of the video modulation depend on the transponder bandwidth available. Typical values for network TV are a peak deviation of 10.75 MHz and a maximum video modulating frequency of 4.2 MHz that requires a 29.9 MHz transponder bandwidth. And hence the conventional satellite television receivers must demodulate the incoming FM signals, recover the baseband video and audio channels, and re-modulate the audio and video onto a locally generated carrier using the same modulation scheme as a broadcast TV transmitter. And this provides the basic consideration for a Satellite receiver design. Satellite Applications 14 1. Satellite Communication Applications : a. Satellite Television b. Direct Broadcast Satellites c. Cable TV (CATV) d. Direct Home Reception e. Telephone Services via Satellite f. Data Communication Services g. Data broadcasting using Satellite h. Interactive data communication 2. Remote sensing and Earth observation Application : a. Cartography b. Monitoring agriculture and Forestry c. Oceanography d. Ice Reconnaissance e. Monitoring Oil pollution and Air pollution f. Snow melts g. Mineral and Oil Exploration 3. Meteorological Applications : a. Satellites for Weather Forecasting 4. Military Application : a. Recondition arid Intelligence gathering functions b. Command and Communication c. Navigation Satellite d. Early warning Satellite e. Meteorological functions f. Nuclear detection 5. Scientific and Technological Applications : Satellite for science studies 15 Microwave Communication Why microwave ? Microwaves have been used in Satellite communication for five specific reasons. First, higher frequency electromagnetic waves have the potential for relaying larger quantities of information because, as the frequency increases, any given bandwidth becomes a smaller fraction of the FM modulated carrier wave frequency. To illustrate, a 1 MHz wide band of signals imposed on a 10 MHz carrier of the spectrum modulates the carrier by 10 percent while the same bandwidth modulates a 10 GHz carrier by 0.1 percent. Since more bandwidth is available, wider bands with higher information capacities can be used at the higher microwave frequencies. Therefore, microwaves can relay more information per Satellite than lower frequency signals and thus can payoff the expensive investment in Satellite launching, operation and maintenance more quickly. A second reason for using microwaves stems from the requirement for uplink antennas to aim a highly directional beam towards an extremely small target in space. Physics dictates that an antenna that is substantially larger than the wavelength of radiation it is managing can better focus electromagnetic waves. For example, sending a directional beam of an AM radio signal having a 100-meter wavelength would require an extremely large, cumbersome and expensive antenna. Since 6 GHz microwaves have wavelengths of approximately 2 inches (5 cm), a 15-foot uplink dish can aim most of its radiation into a very narrow beam, and relatively low power can be used. Third, microwave transmissions to Satellites or between earth - based, line-of-sight relay stations are not as susceptible to noise from atmospheric disturbances as are lower frequency transmissions. To illustrate, several times each year, for periods as long as two or three days, short-wave radio is use-less for long distance communication because sunspot activity disturbs the required reflection of these relatively low frequency radio waves by the upper atmosphere. Fourth, the most important property of microwaves that determines their use in Satellite communication is their ability to pass through the upper atmosphere into outer space. Below frequencies of approximately 30 MHz, a radio wave will be reflected back from the ionosphere layer in the atmosphere towards earth. Since microwave frequencies are far above the 30 MHz range, they easily pass through the ionosphere shield. Fifth, the microwave region of the electromagnetic spectrum was a virgin territory during the late 1950s and 60s when the FCC and the International Telecommunications Union were allocating frequency spectrum. Many different communication media and users already occupied lower frequency space. As geosynchronous orbital space has become increasingly populated, progressively higher microwave frequencies have been allocated to Satellite communications. Until the early 1980s most Satellite broadcasters used C-band frequencies. Today, portions of the' Kuband are employed and numerous potential users are eyeing higher frequency bands. However, a technical difficulty lies in this path. Microwaves are depolarized and more strongly absorbed by water vapor in the atmosphere at higher frequencies. So higher power transmissions must be used to counteract this effect. 16 Frequency Bands (MW) : Band Name : Bandwidth (GHz) : 0.39 to 1.55 L- band S- band : 1.55 to 5.20 C- band : 3.70 to 6.20 : 5.20 to 10.9 X- band K- band : 10.9 to 36.0 If Satellite broadcasters had been allocated space in the S-band in the pioneer days of Satellite TV, perhaps lower cost, more readily available techniques could have been used. The equivalent of the FCC in India recognized this loss caused by absorption in the atmosphere. They now use 2 GHz, S-band Satellite relays. Channel Formats (TV) : The number of television channels, telephone conversations or the amount of data transmitted is related to the electronic design of a Satellite. The early Western Union vehicles such as Westar I and II relayed twelve television programs simultaneously; the RCA series of Satcom and most modem C-band broadcast Satellites handle at least twenty four channels. How is the number of channels determined? The 500 MHz microwave band can be subdivided into twelve 40 MHz segments plus a remainder of 20 MHz. Since a 36 MHz bandwidth is sufficient to broadcast a high quality television picture. Western Union designed their early Satellites to carry 12 channels having 36 MHz bandwidths with 4 MHz protection regions, guard bands, between each channel to eliminate the possibility of crosstalk. Each channel was handled separately on-board the Satellite by a device called a transponder. Engineers designing the satcom I vehicle were somewhat more creative. They doubled the number of channels which could be relayed by this 500 MHz total bandwidth by a technique called frequency re-use. All even channels were transmitted earthward with horizontal polarization; all odd channels were sent with vertical polarization; and the frequency centers of these cross polarized channels were offset from each other for further security against cross-talk. Since each earth station was equipped to detect only vertical or horizontal polarization at one time there could be some overlap between the frequencies used for the odd or even channels. Note that the format used for US broadcast Satellites is by no means the only one accepted by other nations. For example, European Satellites relay their television broadcasts over 700 MHz bandwidth. Twelve C-band channels have 36 MHz bandwidths while six trans-ponders have 72 MHz bandwidth. 17 Channel Formats (audio) : Each transponder manages a 36 MHz wide band of frequencies. When an earth station receives and processes this information, the resulting signal is contained in a band of frequencies from near zero to about 10 MHz. The video signal is contained between zero and 4.6 MHz. All the remaining space can be used for audio channels, some of which carry stereo or mono sound that matches the television picture while others carry totally separate messages. These audio signals are carried on “audio sub Carriers”. Most U.S, television broadcasts relay the audio information on a 6.8 MHz sub carrier or occasionally, on both 6.2 and 6.8 MHz sub carriers for transmitting stereo sound. Some Satellite transponders operate in the single channel per carrier mode, known as SCPC, where only audio information is relayed. Satellite Channel Frequencies : Downlink Transponder Number Frequency (MHz) 1. 3720 2. 3740 3. 3760 4. 3780 5. 3800 6. 3820 7. 3840 8. 3860 9. 3880 10. 3900 11. 3920 12. 3940 13. 3960 14. 3980 15. 4000 16. 4020 17. 4040 18. 4060 19. 4080 20. 4100 21. 4120 22. 4140 23. 4160 24. 4180 18 General Structure of Satellite Communication System 1. Antennas : a. General Aspect : An antenna may be defined in the following way. To radiate or receive electromagnetic waves an antenna is required. Antenna or aerial is system of elevated conductors which couples or matches the transmitter or receiver to free space. A transmitting antenna connected to a transmitter by transmission line, forces electromagnetic waves into free space which travel in space with velocity of light. Similarly, a receiving antenna connected to a radio receiver, receives or intercepts a portion of electromagnetic waves through space. Thus radio antenna is defined as the structure associated with region of transition between a guided wave and a free space wave or between a free space wave and guided waves. The official definition of antenna according to the institution of electrical and electronics engineers is the simply a "means for radiating or receiving radio waves". A Satellite antenna intercepts the extremely weak microwave transmission from a targeted Satellite and reflects the signal to its focal point, where the feed horn is placed. This is the process that concentrates the signal so that the necessary power is available for subsequent electronic components. The quality of a Satellite antenna, often simply called a dish, is determined by how well it targets a Satellite and concentrates the desired signal and by how well it ignores unwanted noise and interference. Dishes must be durable and able to withstand winds as well as other natural and manmade forces. In order to be able to compete in the marketplace, they also must be aesthetically pleasing and affordably priced. b. Microwaves Antennas : UHF and SHF bands are respectively 300-3000 MHz and 3000-30000 MHz. Microwave region starts from 1000 MHz and extended up to 100000 MHz. The corresponding wavelength is in centimeters 10-1 cm and less. The transmitting and receiving antennas for use in the microwave spectrum tend to be directive i.e. high gain and narrow beam width in both horizontal and vertical planes. Theoretically all the antennas and antenna-array could be used at all frequencies but in practice the actual shape of antenna can be large and are used either singly or in array at UHF and SHF but another types utilizing reflecting or radiating surfaces are generally more practical and hence used extensively. As the frequency increases, the wavelength decreases and thus it becomes easier to construct an antenna system that is large in terms of wavelengths and which therefore can be made to have greater directivity. At microwave frequencies the physical size of a high gain antenna becomes 19 small enough to make practical the use of suitably shaped metallic reflectors to produce the desired directivity. Here reflectors are curved surfaces, unlike previously where it was plane surface. The most important practical antennas in microwave frequencies range are. i. Parabolic reflector or microwave dish. ii. Lens antenna iii. Horn antenna Parabolic reflectors and lens antennas are based on the geometric optical principles. Their feed methods are also not by coaxial etc. but by optical methods. c. Antennas with Parabolic Reflectors : A parabola may be defined as the locus of point, which moves in such a way that its distance from the fixed point (called focus) plus the distance from straight line (called directrix) is constant. A parabola is a two-dimensional plane curve. Its equation is : 2 y= 4fx The open mouth (D) of the Parabola is known as the Aperture. The ratio of focal length to Aperture size (i.e. f/D) known as "f over D ratio" is an important characteristic of parabolic reflector and its value usually varies between 0.25 to 0.50. Focusing or beam formation action of parabolic reflector can be understood by considering a source of radiation at the focus. Let a ray starts from the focus (F) at an angle 0? w.r.t. parabolic axis. Alternatively, all the waves emanating from the source at focus and reflected by parabola are traveling the same distance in same time in reaching the directrix and hence they are in phase. The principle of equality of path by length is maintained between all rays of two wave fronts. Putting in another way where there is path length difference between the two wave fronts. Two rays cancellation action will take place. Hence the geometrical properties of parabola provide excellent microwaves reflectors that lead to the production of concentrated beam of radiation. In fact, parabola converts a spherical wave front coming from the focus into a plane wave front at the mouth of the parabola curve as spherical, appears as minor from the focus, which is not striking the parabola curve as spherical, appears as minor lobes. Obviously this is wastage of power. This is minimized by partially shielding the source. Further if a beam of parallel rays is incident on the parabolic surfaces they will be focused at a point i.e. Focus. This is in effect due to the principle of reciprocity theorem which says that properties of an antenna are independent whether it is for transmission or reception case also as rays coming perpendicular whether it is for transmission or reception case also 20 as rays coming perpendicular to directrix will be focused at the focus and other due to path length difference parallel rays are known as collimated. d. Antenna Efficiency : Antenna efficiency is a measure of how much signal is actually captured by the dish and feed-horn/LNB assembly. A perfect, 100 percent efficient dish would therefore direct all the power intercepted from a broadcast Satellite into the feed horn. Efficiency is determined by the surface accuracy of the antenna, by losses that occur when microwaves are not perfectly reflected but absorbed by its surface, by reflective losses from components sited in the path of the incoming rays such as the feed horn and its supports, and by how much "spill over" occurs. Typical efficiencies range from lows of 40 percent for quite poorly designed systems to as high as 65 or 70 percent for high quality antennas. Offset fed antennas can have efficiencies in excess of 80 percent because there are no structures between the incoming signal and the dish surface that reflect the incoming signal energy. 2. Earth Stations : The base band signal from the terrestrial network enters the earth station at the transmitter after having processed (buffered, multiplexed, formatted etc) by the base band equipment. After the encoder and modulator have acted upon the base band signal, it is converted to the uplink frequency. Then it is amplified and directed to the appropriate polarization port of the antenna feed. The signal received from the Satellite is amplified in an LNA first and is then down converted from the down link frequency. It is then demodulated and decoded and then original base band signal is obtained. The isolation of low noise receiver from the high power transmitter is of much concern in the design considerations of the earth stations. There may also be Satellite/earth terminal mutual interference effects. Other sources of interference include ground microwave relay links, sun transit effects and inter modulation products generated in the transponder or earth terminal. 21 3. Satellite Receiving System : Figure 3 a. Dish Antenna : To receive signal from the Satellite dish antenna are used. They are parabolic in shape. A dish antenna collects the signal coming from the Satellite & focuses it at a point known as Focal point. Dish antenna is used to obtain VHF & UHF signals. For different frequency ranges different size of dish antenna are used. The size of dish antenna depends on wave length of the signal. For UHF range the size of the dish antenna is 3 to 5 m & for signal up to 12 GHz the size is 91 to 180 cm. These are made of fiber glass. The reflector at the dish antenna is made up of aluminum or fiber glass for different frequency the depth of the dish antenna is also different. The different parts of dish antenna are : i. Stand or Base Support ii. Parabolic reflector. iii. Mechanisms for rotating dish antenna horizontally & vertically. iv. LNB mounting etc. b. Feed Horn : A dish antenna receives the signal coming through a very large area, these get reflected to a point, at that point a pipe type instrument is fitted. This pipe type instrument is known as Feed Horn. From the feed horn the signals are given to LNB. It is made in such a way that it can receive maximum signal on adjustment. It is adjusted on the basis of picture & sound quality reception. It acts as impedance matching amplifier. c. Low Noise Block (Down Converter) : Most important part mounted on the disk antenna is LNB. The signal from the feed horn is fed to LNB. These are of SHF range & contain unwanted frequencies. This high frequency cannot be fed directly to TV. Theoretically 22 LNB converts high frequency range to low frequency range & also removes noise. In Satellite reception different LNB are used for different frequency ranges. There is a high frequency amplifier in LNB to amplify the faded signals coming from the Satellite. Now this signal is converted into low frequency of definite amount. There is a high frequency local oscillator & mixer inside a LNB. The amplified signal from the amplifier and the signal from the local oscillator come to the mixer sections just like that in the normal tuner. The LNB used for C band reception gets the input of 3.7 to 4.2 GHz & the output is 950 to 1450 MHz. The output signals are then fed to Satellite receiver through coaxial cables. d. Satellite Receiver : The signals from the LNB, which is of the range 950 to 1450 MHz reaches to Satellite receiver. This signal contains all signals coming from the Satellite. Satellite receiver firstly selects the desired frequency from the input signal. Then it converts this signal to the tuners input range. But the signal coming from LNB (950-1450 MHz) is more than the input range of TV receiver. The signals coming from the local transmitter employs FM for audio & AM for video but in the case of Satellite transmission both audio & video are transmitted through FM. Therefore signal needs to be converted according to the TV receiver. The tuner employed in Satellite receiver is different from the TV tuner. It is known as Wide Band Tuner. It selects the desired frequency through a selector section in the tuner. It works on the principle, which is the same as that of electronic tuner i.e. desired channel is selected by changing the voltage. Now this frequency is amplified & sent to mixer section. There is local oscillator also. This section generates the frequency range of 1560 to 2360 MHz. This is voltage controlled oscillator. The mixer stage generates a new frequency signal known as IF signal. It is amplified & passed through band pass filter. This controls the gain of the signal. It is amplified by IF amplifier & given to PLL section. This PLL section demodulates the signal & the new signal is generated known as Base Band signal. This signal is given to the different sections of PLL. Medium Frequency & High Frequency are used in Radio receivers. VHF & UHF bands are used for TV transmission. In VHF band 40 to 230 MHz. is only used from the whole range, in the same way 470 to 890 MHz. is only used for UHF band. Microwaves are the electromagnetic waves of the wavelength 3mm to 1.3 m. & having frequency range of 225 MHz to 100 GHz. Therefore VHF to EHF bands can be considered as Microwaves. 23 Orbital Aspects of Satellite Communication Orbital Mechanics : For the equation of orbit we use rectangular coordinate system. We assume that origin is center of earth & z-axis extends towards North Pole. The coordinate system is in free space and earth is rotated in z-axis, the center of earth - satellite coincides with center of mass at origin. As shown in figure. Figure 4 By using Kepler's law : we have equation for orbit is as r = p / (1 + e cosk) 0 2a = p / (1 , e) 2b = a / ,(1,e) Perigee : The point in orbit where the Satellite is closest to earth is called perigee. Apogee : The point where Satellite is farthest from earth is called apogee. Kepler's II law of planetary motion : The differential area swept out by radius vector r from origin to the Satellite is equal in equal time. 3/2Time period T = 2 J Ia / ,, 2223 Or T = 4J I a / , 24 Figure 5 Kepler's III law of planetary motion : Square of period of revolution is proportional to cube of semi major axis. The above equation proves it. Geostationary orbits take earth rotation period equal to 86400 s (24 hrs). Substitute this in above equation, we get a = 42241.558 Km. Since a geostationary Satellite must have a constant angular velocity, orbit must be circular and radius equals to 'a' of semi-major axis. It will assume 42,242 Km. This orbit lies in equatorial plane. Effect of Earth's Oblateness : Since the earth is not a perfect sphere with a symmetrical distribution of mass, its gravitational potential does not have simple (l/r) dependence, the earth gravitational potential is represented more accurately by the expansion in Legendre Polynomial j in , acceding powers of (earth's radius, e) / (orbital radius r). In this expansion the dominant 2term is j(re/r), its value is called the j coefficient. The effect of this term is to cause an 2 2 unconstrained geo synchronous satellite to drift towards and circulate around the two nearer two stable point s. These correspond to sub-Satellite longitudes of 105? Wand 75? E, location called "graveyards" because they collect old Satellite whose station keeping fuel is exhausted. Effects of Sun And Moon : Gravitation attraction by sun and moon causes the orbital inclination of a geosynchronous Satellite to change with time. If not countered by north-south station keeping, these forces would increase the orbital inclination from initial 0? at launch to 14.67?, 26.6 years later. The rate of change varies with the inclination of moon's orbit, but values of about 0.86?/ year. Sun Transit Outage : When the sun passes through the beam of earth station antenna, the overall receiver noise level will rise significantly and interfere with or prevent normal operation. This effect is predictable and can cause outage for as much as 10 minutes a day or for several days and for about 0.02% of an average year. A receiving earth station can do nothing about it except wait for the sun to move out of the main lobe of antenna. 25 Launches and Launch Vehicles : For a spacecraft to achieve synchronous orbit, it must be accelerated to a velocity of 3070m/s in a zero inclination orbit and raised to a distance of 42242 km from center of earth. There are two competing technologies for doing this expandable launch vehicle (ELV) and space shuttle (STS). Satellite Life and Maintenance : Maintaining a microwave communication system 35800 km out in space is not a simple problem, so communication Satellites are very complex, extremely expensive and also expensive to launch. For ex. INTEL V Satellite cost around $50M. The cost of spacecraft and launch are increased by the need to dedicate an earth station to the monitoring and control of Satellite, at a cost of several million dollars per year. Communication Satellites are designed to have an average operating life time of 5 to 10 years. The designer must provide that Satellite that can survive a hostile environment of outer space for that long. In order to support the communication system, the spacecraft must provide a stable platform on which to mount antennas, be capable of station keeping, provide the required electrical power for the communication system, and also provide temperature controlled environment for communication electronics. Satellite Sub Systems In this section we will discuss the subsystems that are needed on a spacecraft to support its primary mission of communication. Altitude and Orbit Controlled System (AOCS) : This subsystem consists of rocket motors that are used to move the Satellite back to the correct orbit when external forces cause it to drift off station and jets inertial devices that controlled the attitude of Satellite. There are number of factors that tends the Satellite to rotate like gravitation field forces of Sun. Earth and Moon and other planets will set up rotation motion if Satellite is not perfectly balanced. Solar pressure acting on solar panels, antenna and Satellite may also create rotational forces. Because the Satellite moves round the earth's center in its orbit, the forces described vary cyclically through a 24hour period. This tends to set up notation (a wobble) of Satellite, which must be dumped out mechanically. The variation in the gravitational field that causes altitude changes will also create accelerations on the Satellite tending it changes its orbit. The major influence is the moon's gravitational field, which is about three times stronger than sun's gravitational field at geo stationary altitudes. Since neither the earth's orbital plane round the sun nor moon's orbital plane around the sun lies in earth's equatorial plane, there is resultant gravitational forces that acts to modify the inclination of the Satellite orbital plane. The rate of inclination was about 0.85? per year initially for a geostationary Satellite in 1970-80. If no north-south station keeping correction were applied, the orbit inclination would increase to maximum of 14.67? from initial 0? in 26.67 years. The inclination would then decrease back to zero in similar time period. The earth is not truly spherical, there is a bulge in the equator region of about 65 m longitudes of 15? Wand 165? E, with the result that Satellite experience an acceleration 26 towards a stable point in geostationary orbit at longitude 105? W or 75? E. For accurate station keeping, the Satellite must be accelerated in opposite direction by firing rocket motors, or thruster, at a periodic interval. The earth is also flattened at the poles by about 20 Km, but it has little influence on geostationary Satellite. There are two ways to make a Satellite stable when it is in orbit and weightless. The entire body of the Satellite can be rotated at 30 to 100 rpm to provide a powerful gyroscopic action, which maintains the spin axis in the same direction; such Satellites are called spinners. Alternately, the momentum wheel can be mounted in three mutually orthogonal axes. The momentum disc is generally a solid disc driven by motor, rotation at high speed within a sealed, evacuated housing. Increasing the speed of the wheel means increasing its angular momentum, which causes the Satellite to recess in the opposite direction, according to principle of conservation of angular momentum. Power System : All communication Satellites drive their electrical power from solar cells. The power is used by communication system, mainly in transmitters and other parts of Satellite. In the total vacuums of outer space at geostationary altitude, the radiation falling on the 2Satellite is having intensity of 1.39 KW/m. Solar cells do not convert all the incident energy into electric power as their efficiency is typically 10 to 15 percent and also falls with time because of aging of cell and etching in surface by micrometer impacts. An electrical motor once per 24 hr to keep the cell in full sunlight must rotate solar cells. This causes heating of cell typically to 50? - 80? C, which causes drop in output voltage at the rate of 2mV/:C. Communication Sub System : The communication subsystem is the major component of a communications Satellite, and the remainder of the spacecraft is there solely to support it. Frequently the communication equipment is only a small part of the weight and volume of the whole spacecraft. It is usually composed of one or more antennas, which receive and transmit over wide bandwidths at microwave frequencies, and set of receivers and transmitters that amplify and retransmit the incoming signals. The receiver- transmitter units are known as transponders. Transponders : The transponder is high frequency radio receiver, a frequency down converter, a powerful amplifier used to transmit downlink signal. It receives a modulated signal, on a carrier signal frequency and retransmits the same signal information on a lower carrier frequency with no demodulation. The RF signals from the receiving antenna are separated from each other by use of band pass filter, and then a heterodyne downward to the downlink frequency. Each signal is filtered again to pass only the difference frequency, amplified, in some case limited, and then fed into travelling wave tube to be powered for trip back to the earth. In single transponder Satellite in C-band, local oscillator operated at the frequency higher than RF antenna signal and simple low pass 27 filter than separates the difference frequency from higher sum, RF and oscillator. Each uplink carrier signal is lowered by the same amount for each channel to its associated down link carrier frequency. On simple relay channel systems, the multi-transponder system consists of 12-24 individual receivers that share a common local oscillator at 2225 MHz. In more sophisticated systems, either frequency division multiplexing (FDMA) or time division multiplexing (TDMA) formatted signal is used to make on board system more efficient and flexible. One such system is shown in figure that includes a routing control channel, switching network for address codes, and frequency synthesized mixer circuit. The address data is mixed with the message package assembled at ground station for each message signal group. The address data is extracted before the carrier is reduced in frequency and is used to control switching system at the input of the mixer. The entire message from one ground station may not have the same final destination. By time-sharing the message may be routed by TDMA control. By controlling the final output signal, the power to a given footprint may be adjusted separately for each down link transmission. Transponder Figure 6 Spacecraft Antennas : These can be considered separately from the transponders. On advanced Satellites, the antenna systems are very complex and produce beams with shapes carefully tailored to match the areas on the earth's surface served by the spacecraft. Four main types of antennas used on Satellite are : 1. Wire antenna 2. Horn antenna 3. Reflector antenna 28 4. Array antenna Wire antennas are used primary at VHF and UHF to provide communication for telecommunication systems. They are positioned very well with great care on body of satellite in an attempt to provide omni-directional coverage. An antenna pattern is a plot of the field strength of far field of the antenna when the transmitter drives antenna. It is usually measured in decibels (dB) below the maximum field strength. The gain of antenna is measure of antenna's capabilities to direct energy in one direction. The pattern is frequently specified by 3-dB beam width, the angle between the direction in which the radiated or received field falls to half the power in the direction to maximum field strength. However the Satellite antenna is used to provide coverage of certain area, or zone of earth surface and it is more useful to have contours of antenna gain. Horn antenna is used at microwave frequencies when relative wide beam is required, as for global coverage. A Horn is flared section of waveguide that provides an aperture several wavelengths wide and a good match between the waveguide impedance and free space. Horn is also used for feeds for reflection either single or in clusters. It is difficult to obtain gain much greater than 23 dB or beamwidth narrower than about 10: with horn antenna. For higher gain array can be used. Reflector antennas are usually illuminated by one or more horns and provide a larger aperture than active by horn alone. For maximum gain it is necessary to generate a plane wave in the aperture of the reflector. This is achieved by choosing the reflector profile that has equal path lengths from the feed to the aperture so that all the energy radiated by the feed and reflected by the reflector reaches the aperture with the same phase angle and create a uniform phase front. One reflector shape that achieves this with a point source of radiation is the paraboloid, with a feed placed at its focus. The basic shape of most reflector antennas are modified paraboloidal reflector antennas, although many Satellite antenna reflector used modified paraboloidal reflector profiles to tailor the beam pattern to particular coverage zone. Telemetry, Tracking And Command (TT & C) : These systems are partly on Satellite and partly on controlling earth station. The telemetry system sends data derived from many sensors on the spacecraft, which monitors the health of spacecraft via a telemetry link to the controlling earth station. The tracking system is located at the earth station and provides information on the range and elevation angle and azimuth angle of the Satellite. Repeated measurement of these three parameters permits computation of orbit elements from which changes in the orbit in the Satellite can be detected. Based on telemetry data received from Satellite and orbital data obtained from tracking system, the control system is used to correct the position and attitude of Satellite. It is also used for controlling' antenna pointing and communication system configuration to suit current traffic requirements, and to operate switches on the Satellite. Satellite Link Design [An Over View :] This is only a theoretical over view. For details some standard text book or journal should be consulted. 29 General Aspects : The design of a Satellite receiver as an integral part of a Satellite communication system is a complex process, involving compromises between many factors in order to obtain the maximum performance at an acceptable cost, the major factors dominating the design of any system using geostationary Satellites are : 1. The DC power that can be generated on board Satellite and hence the limited transmitted output power. 2. The frequency bands allocated for Satellite communication. 3. The maximum dimensions of Satellite and ground station antennas. 4. The multiple access technique used to share communications capacity between many earth stations. The limited size of a Satellite puts an upper limit on the DC power available for transponders. The size limitations combine to produce a situation in which the Satellite has a limited RF output power, which cannot be concentrated onto very small areas of the earth because of the limited size of the Satellite antennas. The resulting flux density at the earth's surface for a typical communication Satellite is very small about - 127 2dBW/m. Second is the selection of frequency bands. In general, it is easiest and cheapest to use the lowest available frequency. However, bandwidth is limited in the lower frequency bands, and interference is more likely, as these frequencies are already heavily used by terrestrial systems. The higher frequencies offer the advantages of wider bandwidths e.g. 3.5 GHz at 30/20 GHz against the 1000 MHz available in the 6/4 GHz band. But propagation difficulties are very high above 10 GHz. The 6/4 GHz bands have been the most popular because they offer the fewest propagation problems and, historically RF components for these bands have been readily available. In this case our aim is to receive this weak signal and to recover the transmitted information. A communication system must be designed to meet certain minimum performance standards, within limitations of transmitter power and RF bandwidth. The most important performance criterion is the signal to noise ratio (SNR) in the information channel, which carries the signal in the form in which it is delivered to the user. In designing a Satellite communication system, we must try to guarantee a minimum signal to noise ratio in the receiver's baseband channels and also meet constraints on Satellite transmitter power and RF bandwidth. The signal to noise ratio in a baseband channel depends on a number of factors; the carrier to noise ratio (C/N) of the RF or IF signal in the receiver, the type of modulation used to impress the base band signal onto the carrier, and the IF base band channel bandwidths in the receiver are the most important. Firstly we are concerned mainly with the design and analysis of Satellite communication links in terms of the carrier to noise ratio. Thus we need to be able to calculate carrier (received) power in an earth station receiver, and also the noise power in the receiver, to establish the C/N. The calculation of the power received by an earth station from a Satellite transmitter is fundamental to the understanding of Satellite communication. Consider a transmitting 30 source, in free space, radiating a total power P, Watts uniformly in all directions called t an isotropic source. At a distance R from the hypothetical isotropic source, the flux density crossing the surface of a sphere, radius R, is given by 22F = P / 4,R Watts / m t In practice we use directive antennas to constrain out transmitted power to be radiated primarily in one direction. The antenna has a gain G (6) in a direction 6, defined as the ratio of power per unit solid angle radiated in a given direction to the average power radiated per unit solid angle: G (,) = P (,) / (P/ 4,) 0 Where P (,) is the power radiated per unit solid angle by the test antenna. G (,) is the gain of the antenna at an angle. The reference for the angle is usually taken to be the direction in which maximum power is radiated, often called the boresight of the antenna. Thus for a transmitter with output PWatts driving a loss less antenna with gain Gt , the flux density in the direction t of the antenna boresight at distance R meter is 22F = P G/ 4, R Watts / m tt The product PG is often called the effective isotropically radiated power or EIRP, and tt it describes the combination of transmitter and antenna in terms of an equivalent isotropic source with power PG Watts, radiating uniformly in all directions. If we have tt2an ideal receiving antenna with an "aperture area of A m, we would be able to collect power P Watts given by the product (F*A). But a practical antenna with a physical r2aperture area of Am will not deliver the power given in the previous equation. Some r of the energy incident on the aperture is reflected away from the antenna, and some is absorbed by lossy components. This reduction in efficiency is described by using an effective aperture Ae, where A = , A er And , is the aperture efficiency of the antenna. Thus, the power received by a real 2antenna with a physical receiving area A and effective aperture area Am is re 2P = P G A / 4,R Watts rtte It may be noted that the power received at an earth station depends only on the EIRP of the Satellite the effective area of the earth station antenna and the distance R. The equation is essentially independent of frequency within a given band. Now the gain and area of an antenna are related as. 2G = ,,,e/ , r Substituting for A in equation for P gives er 2P = P G G / [,/4,R] Watts rttr 31 This expression is known as the Friis transmission equation, and it is essential in the 2calculation of power received in any radio link. The term 1/ [,/4, R] is known as the path loss, L. Thus we can write. p Power received = (EIRP * Receiving antenna gain) / Path loss And in decibel terms, we have P = (EIRP + G, L) dBW rr p Above equation represents an idealized case, in which there are no additional losses in the link. In practice, we need to take into account the losses in the atmosphere due to attenuation by rain, losses in the antennas at each end of the link, and possible loss of gain due to antenna mis-pointing. All these factors are taken into account by the system margin. So above equation. can now be written as P = (EIRP + G , L, L, L , L) dBW rrp a tara Where L is the attenuation in the atmosphere. a L are the losses associated with transmitting antenna. ta L are the losses associated with receiving antenna. ra The received power P, calculated by the above equations is commonly referred to as r carrier power, C. This is because most Satellite links use either frequency modulation for analog transmission or phase modulation for digital systems. In both these modulation systems, the amplitude of the carrier is not changed when the data are modulated onto the carrier, so carrier power C is always equal to received power P. r Noise figure and Noise Temperature : Noise figure is frequently used to specify the noise generated within a device. The operational noise figure is defined by the following formula : NF = (S / N) / (S / N) inout Because noise temperature is more useful in Satellite communication systems, it is best to convert noise figure to noise temperature, T. The relationship is d T = T (NF ,1) d0 Where, T is the reference temperature used to calculate the standard noise figure 0 usually 290K. 32 Design of Downlinks : The downlinks of any Satellite communication system must be designed with the following objectives : 1. To guarantee continuity of the link for a specified percentage of the time (typically 99.9 percent), with a given (SIN). 2. To carry the maximum number of channels at a minimum capital and maintenance cost. . The first objective requires a minimum (S/N) at the receiver input for 99.9 percent of the time, and will almost certainly require a modulation scheme or signal-processing technique that gives a (S/N) improvement over the receiver (S/N). Modulation is usually FM in analog system and PSK on digital system, but companded SSB is also used. Thus in order to maintain satisfactory communication, the (C/N) must remain above threshold under all conditions; e.g. for an FM system, the threshold is in the range 4 dB to 15 dB depending on the type of demodulator used. For PSK systems it is typically 8 dB to 15 dB. Then an allowance, called the system margin of few dB is usually made for propagation and equipment degradation. The second objective brings in a series of compromises between antenna cost, receiver cost, tracking accuracy, station maintaining, modulation, and multiple access techniques. For any standard earth those specifications are produced, which go some way to optimizing the earth segment of that particular system. 33 Basic Receiving System Super Heterodyne Receiver : The Radio Receiver used in AM system is called the super heterodyne receiver. It contains. 1. RF amplifier section 2. A frequency converter 3. Intermediate frequency amplifier 4. Envelope detector 5. Audio amplifier Super Heterodyne Receiver Figure 7 1. RF Amplifier : The antenna signal is fed to the RF amplifier. The signal at the antenna has the lowest noise level that will be found anywhere in the receiver. All following amplifiers add some noise to the signal so a major function of RF amplifier is to provide gain at the point of lowest noise in the system. In many receivers the RF amplifier also participates in selecting the signal to be processed through the receiver. Some receivers have more than one RF amplifier & some have none. The RF amplifier is often a tuned input tuned output amplifier with a typical voltage gain. "RF amplifier is basically tunable filter and an amplifier that picks up the desired station signal by tuning the filter to the right frequency band". 34 2. Frequency Convertor (Mixer) : The output signal from the RF amplifier is coupled to a mixer amplifier. The word mixer indicates to that there is more than one signal fed into this section. Indeed there are two signals, with the second signal coming from a local oscillator. It has a high and low frequency input signal, it is biased nonlinearly and it will produce the sum and difference frequencies. In the receiver, the effort of the mixer is to down shift the carrier signal to an intermediate frequency rather than to shift it up. The local oscillator may be operated above or below the frequency of the incoming RF signal. There are few differences in the local oscillators found in the receiver that embraces the super heterodyne format of circuitry. The function of local oscillator is to supply a sine wave signal to be used at mixer to reduce the RF carrier frequency to the IF carrier frequency. Two limitations are placed on oscillator performing this function : a. They must be spectrally pure, that is, low in distortion and free of harmonics. This condition helps in determining the receiver quality and ease of alignment. b. The oscillator must be frequency stable. It should not drift off frequency due to changes in temperature or to component aging. The oscillator frequency may be higher or lower than the selected RF signal by an amount equal to IF. 3. IF Amplifiers : The mixer being the true modulator has an output that contains the two original frequencies plus the sum and the difference frequency of the input signal. Basically an IF amplifier can suppress the undesired signal and only amplify the required channel signal, IF section can effectively suppress the adjacent channel interference because of its high selectivity. For example in a Satellite receiver system the down link signal coming from the Satellite which is of frequency range 3.7 to 4.2 GHz down converted into 950 to 1450 MHz. The converter inside the LNB compresses a fixed frequency oscillator running at 5150 MHz, which beats with the incoming signal frequency. The difference frequencies obtained range from 5150 – 4200 = 950 MHz, to 5150- 3700 = 1450 MHz, i.e. the input frequency range of 4.2 GHz to 3.7 GHz is converted to 950 to 1450 MHz range. In a system in tuner section with the mixer stage there is local oscillator section. This is basically voltage- controlled oscillator (VCO). In this way the two signals coming to the mixer stage generate a new frequency signal and this only signal is called as the IF signal. Now this signal is given to this VIF section where it is amplified and given to the band pass filter and it control its gain then after it is given to IF amplifier, which again amplifies required signal. And the signal passes to the PLL section, which demodulate this signal and convert it into a new signal and this is the BASEBAND signal. In this way IF section basically acts as a tunable amplifier that amplifies selective signal and suppress other adjacent channel signal. Double Conversion Receivers : 35 Receivers in the high frequency RF range are more likely than the low frequency receivers to incorporate double-conversion front end circuitry. This is due to wide frequency spread between the RF signal and the standard IF signal used in our receiver system that is highly sensitive receiver for high frequency work. The system is called the double conversion system because the RF frequency is reduced to the IF frequency in two steps. There are several advantages to use double conversion : 1. The RF signal is reduced to a very low intermediate frequency, which is less problematic and which provides gain bandwidth product feature better suited to stable circuits. 2. Above feature of double conversion provides better selectivity feature. 3. Double conversion system have a better image rejection ratio than the single conversion system; Image Frequency Rejection : It is possible for an unwanted RF signal to get through the RF amplifier and mix with the oscillator signal, and appear along with the desired signal at the intermediate frequency to be amplified. An image is the signal that is the same distance from local oscillator frequency as the desired signal, but in the opposite direction. When the oscillator operates at a frequency higher than the desired RF signal, the image frequency is : Image frequency = RF + 2 IF When the local oscillator operate at the frequency below the RF signal then the image frequency is : Image frequency = RF , 2 IF The rejection of the image frequency signal is dependent on the ratio of the wanted to unwanted signal frequencies and on the Q of the resonant circuit that precede the mixer amplifier. The attenuation in decibels of an image frequency signal may be found by : 22Image frequency (dB) = 20 log , Q F t Where, Q is the total Q of the system. In a preselector receiver, in which no RF t amplifier is used, Q represents the Q of the preselector tuned circuit. In circuit that have t a tuned input tuned output RF amplifier the total Q is found by : 22Q = ,Q + Q ti0 F is the factor that compares the ratio of the image frequency to the desired RF frequency, and is found by F = image / RF , RF / image,,,, For cases where local oscillator operates higher then the RF, or by F = RF / image , image/RF F or cases where local oscillator operates lower then the RF. 36 Understanding Basic Concepts of Satellite Communication Theory : Sinusoidal electromagnetic waves (E/M waves) All radio and television signals consists of electric and magnetic fields which in free 8space travel at speed of light (approx 3 ， 10 meters/seconds), these waves consists of an Electric field (E), measured in Amperes/meter, the E and H field components are always at right angle to each other and the direction of travel is always at right angles of both fields. The amplitudes vary sinusoidally as they travel through space. In fact it is impossible to produce a non sinusoidal E/M wave! (The importance of this statement will be grasped more easily when modulation is discussed.) The Sine Wave : Cycle : One complete electrical sequence Peak Value (V) : Maximum positive or negative value also called amplitude. p Period (t) : Time to complete one cycle Frequency (f) : Number of cycles per second in Hertz. (One hertz = one cycle per second). It follows that period and frequency are reciprocals of each other. T=1/f Commonly used multiplies of hertz are: 3Kilohertz (KHz) =10 Hz = 1000Hz 6Megahertz (MHz) = 10 Hz = 1000000Hz 9Gigahertz (GHz) = 10 Hz = 1000000000Hz RMS Value : This is 0.707 of the peak value and unless otherwise stated, any reference to voltage or current in technical literature is normally taken to mean this value for Example, the supply mains in UK is a sinusoidal variation, stated to be '240 Volts' so the peak value is 240/0.707 = 339 volts. Angular Velocity (w) : This is an indirect way of expressing the frequency W = 2, f rad / sec Instead of considering the no. of complete cycles angular velocity is a measure of how fast the vector angle is changing. The Voltage equation of sine wave which gives the instantaneous value (,) of a sine wave at any point in the cycle is given by: , = Vsin, p For a convenience and brevity, the ,,F part is often lumped together and given the title of angular velocity (,).Using this notation the equation of sine wave can be written as : , =V sin,t p Wavelength : 37 Since E/M waves at a known velocity vary sinusodially, it is possible to consider how far a wave of given frequency (f) would travel during the execution of one cycle. Denoting the speed of light as c the wavelength (,) is given by: , = c / f From this, it so as clear that higher the frequency the shorter the wavelength. Satellite broadcasting employs waves in this order of 10GHz frequency so the order of wavelength can be calculated as follows: 89, = (3 ， 10) / (10 ， 10) -2, = 3 ， 10m = 3 cm. In practice the frequencies used are not necessarily a nice round figure like 10 GHz Nevertheless; the wavelength in present use invariably works out in terms of centimeters. These enormously high frequencies are used in satellite broadcasting? Before this can be answered it is necessary to understand some fundamental laws to broadcasting of information, whether it be sound or picture information. Carrier frequency : For simplicity, assume that it is required to transmit through space a 1000Hz audio signal, in theory an electrical oscillator and amplifier could be rigged up and tuned to 1000 cycles per sec. And the output fed to a piece of wire acting as primitive aerial. It is an unfortunate fact of nature that of nature that for reasonably efficient radiation a wire aerial should have a length some where in order of wavelength of 1000 Hz using the equation given above : 835, = c / f = 3 ， 10 / 10 = 3 ， 10 meters. , = 300000 m which is about 188 miles. Apart from the sheer impractically of such an aerial, waves at these low frequencies suffer severe attenuation due to ground absorption. Another important reason for using high frequencies is due to the considerations of bandwidth, which is treated later. This solution is to use a high frequency wave to carry the signal but allow the Intelligence (the 1000 Hz in our example) to modify one or more of its characteristics. The high frequency wave is referred to as the carrier (F) simply because it carries the c information in some way the method of impressing this low frequency information on to carrier is called modulation. There are two main types of modulation?. Amplitude modulation (AM) and Frequency modulation (FM) 38 Amplitude modulation : The low frequency modulating signal is made to alter the amplitude of carrier at the transmitter before the composite waveform is sent to the aerial system. If the amplitude of the modulating signal causes the carrier amplitude to vary between double its unmodulated height and zero, the modulation is said to be 100 percent. Terrible distortion results if the modulation amplitude is ever allowed to exceed 100 percent. Modulation factor : This is the ratio of modulation amplitude (V) to carrier amplitude (V) mc m = V / V mc When m = 1 the modulation is 100 percent, although 100 percent is an advantage it is too dangerous in practice, due to the possibility of over modulation, so 80% (m = 0.8) is normally considered the safe limit. Sidebands : Although the modulating signal is simple sinusoidal waveforms, in practice it will be more complex. Thus the envelope of the waveform will be non-sinusoidal. The un-modulated carrier sine wave has the instantaneous form: , = V sin,t pc But the amplitude of this wave (V) is made to vary by the modulating frequency which p causes V to have the form : p , = V sin,t pm Substituting this expression in the first equation gives : , = Vsin,t. sin,t mcc We know one of the trigonometric identities Sin A Sin B= ? Cos (A,B), ? Cos (A+B) So it follows that the modulated carrier waveform splits up in space into three pure Sinusoidal components : 1. The carrier frequency 2. The frequency equal to the sum of the carrier and modulating frequencies. This is called Upper sideband. 3. The frequency equal to the difference of the carrier and modulating frequencies. This is called lower sideband. If the carrier frequency is 1000000 Hz and the modulating frequency is 1000Hz then the upper sideband is 1001000 Hz sine wave and lower sideband is 999000 Hz. In practice the modulating frequency will seldom be anything as simple as a 1000Hz sine wave but more probably, May consists of speech or picture information which contains a complex mixture of frequencies. For example, the music frequency extends from about 20 Hz to about 18 KHz so, to transmit high quality sound the upper sidebands 39 would have to contain spread of frequencies extending from 20Hz to 18 KHz above the carrier and the lower sideband frequencies extending 20Hz to 18 KHz below the carrier. Television transmission is more difficult because picture have far greater information content than sound. Wider the sidebands of transmission, greater space will occupy in the frequency spectrum so broadcast stations geographically close together must operate on frequencies well away from each other in order to prevent the interference from their respective sidebands. Since television station occupy several MHz in the spectrum, carrier frequencies are forced into ever higher and higher frequencies as the number of stations fight for space. There are several novel solutions to the overcrowding problem, for example it is not essential to transmit both sidebands since all the required information is contained in one of then, providing of course the carrier is sent with it. Such transmission is contained in one of them, providing of course the carrier is sent with it. Such transmissions are called SSB (single sideband). An even more drastic curtailment is to reduce the carrier at the transmitter to almost zero and use it to synchronize a locally generated carrier at the receiving end a Technique known as single sideband vestigial carrier modulation. Frequency Modulation : Where as amplitude modulation alters the envelope in the vertical plane, frequency modulation takes place in the horizontal plane, the amplitude of the carrier is kept constant but the frequency is caused to deviate proportional to the modulating amplitude. Frequency Deviation : The maximum amount by which the carrier frequency is increased or decreased by the modulating amplitude is called the frequency deviation. It depends up on the amplitude (peak value) of the modulating voltage. In the case satellite broadcasting, the signal beamed down to earth has a typical frequency deviation of about 16 MHZ and the bandwidth occupied by the picture information is commonly about 27 MHz. Modulation index : This is the ratio of the frequency deviation (,f) to the highest modulating frequency (f) m M =,f / fm In contrast with amplitude modulation, the modulation index is not necessarily restricted to maximum of unity. Pre-emphasis (de-emphasis) improvement : Since the noise power density of a receiver demodulator output increases with frequency, high frequencies are boosted or pre-emphasized prior to transmission, when the signal is subsequently demodulated in the receiver the signal and its acquired noise is deemphasized or reduced by an equal amount the overall effect is to reduce the noise component and leads to typical improvement in S/N of 2db for PAL I signals or 2.5 db for NTSC M signals. Noise : 40 An unwanted signal which interferes with reception of the desired information. Noise is often expressed in degrees Kelvin or in decibels. Decibel (dB) : The logarithmic ratio of power levels used to indicate gains or losses of signals. Decibels relative to one watt, milliwatt and millivolt are abbreviated as dBW, dBM and dBmV, respectively. Zero dBmV is used as the standard reference for all SMATV calculations. dB =10 log P / P 12 The sign of result is positive if p is greater than p and negative if p is less than p. 1212 Voltage dB: Although dBs are normally used in conjunction with power ratio, it is sometimes convenient to express voltage ratio in db terms. db = 20 log v / v 12 The use of 20 instead of 10 is because power is proportional to the square of the voltage so the constant is 20 instead of 10. Ku-Band Satellite TV : The microwave frequency band between approximately 11 and 13 GHz used in Satellite broadcasting in European nations. Clarke Belt : The circular orbital belt at 22,247 miles above the equator, named after the writer Arthur C. Clarke, in which Satellites travel at the same speed as the earth's rotation. Also called the geostationary orbit. Antenna : An antenna may be defined in the following way. To radiate or receive electromagnetic waves an antenna is required. Antenna or aerial is system of elevated conductors which couples or matches the transmitter or receiver to free space. A transmitting antenna connected to a transmitter by transmission line, forces electromagnetic waves into free space which travel in space with velocity of light. Similarly, a receiving antenna connected to a radio receiver, receives or intercepts a portion of electromagnetic waves through space. Thus radio antenna is defined as the structure associated with region of transition between a guided wave and a free space wave or between a free space wave and guided waves. The official definition of antenna according to the institution of electrical and electronics engineers is the simply a "means for radiating or receiving radio waves". A Satellite antenna intercepts the extremely weak microwave transmission from a targeted Satellite and reflects the signal to its focal point, where the feed horn is placed. This is the process that concentrates the signal so that the necessary power is available for subsequent electronic components. 41 The quality of a Satellite antenna, often simply called as dish, is determined by how well it targets a Satellite and concentrates the desired signal and by how well it ignores unwanted noise and interference. Dishes must be durable and able to withstand winds as well as other natural and man-made forces. In order to be able to compete in the marketplace, they also must be aesthetically pleasing and affordably priced. Dish Antenna : To receive signal from the Satellite dish antenna are used. They are parabolic in shape. A dish antenna collects the signal coming from the Satellite & focuses it at a point known as Focal point. Dish antenna is used to obtain VHF & UHF signals. For different frequency ranges different sizes of dish antenna are used. The size of dish antenna depends on wave length of the signal. For UHF range the size of the dish antenna is 3 to 5 m & for signal up to 12 GHz the size is 91 to 180 cm. These are made of fiber glass. The reflector at the dish antenna is made up of aluminum or fiber glass. For different frequency the depth of the dish antenna is also different. Feed Horn : A dish antenna receives the signal coming through a very large area, these get reflected to a point, at that point a pipe type instrument is fitted. This pipe type instrument is known as Feed Horn. From the feed horn the signals are given to LNB. It is made in such a way that it can receive maximum signal on adjustment. It is adjusted on the basis of picture & sound quality reception. It acts as impedance matching amplifier. Low Noise Block (Down Converter) : Most important part mounted on the disk antenna is LNB. The signal from the feed horn is fed to LNB. These are of SHF range & contain unwanted frequencies. This high frequency cannot be fed directly to TV. Theoretically LNB converts high frequency range to low frequency range & also removes noise. In Satellite reception different LNBs are used for different frequency ranges. There is a high frequency amplifier in LNB to amplify the faded signals coming from the Satellite. Now this signal is converted into low frequency of definite amount. There is a high frequency local oscillator & mixer inside a LNB. The amplified signal from the amplifier and the signal from the local oscillator come to the mixer sections just like that in the normal tuner. The LNB used for C band reception gets the input of 3.7 to 4.2 GHz & the output is 950 to 1450 MHz. The o/p signals are then fed to Satellite receiver through coaxial cables. 42 Satellite Receiver : The purpose of Satellite receiver is the selection of channel for listening, viewing, or both and transforming the signals in to a form suitable for input to domestic TV and stereo equipment. Various subsections of Satellite Receiver. 1. Power supply 2. Down conversion and tuner circuit 3. Final IF stage 4. FM video demodulator 5. Video Processing Stages 6. Audio processing stages Effective isotropic radiated power (EIRP) and foot print maps the calculation of the power received by an earth station from a Satellite transmitters fundamental to the understanding of Satellite communications. Consider a transmitting source, in free space, radiating a total power P, watt uniformly in all directions called an isotropic t source. At a distance R from the hypothetical isotropic source, the flux density crossing the surface of a sphere, radius R, is given by ,2F = P /,,R Watts/m t In practice we use directive antennas to constrain out transmitted power to be radiated primarily in one direction. The antenna has a gain G (,) in a direction 6, defined as the ratio of power per unit solid angle radiated in a given direction to the average power radiated per unit solid angle: G (,) = P (,)/ (P/4,) 0 Where P (,) is the power radiated per unit solid angle by the test antenna G (,) is the gain of the antenna at an angle The reference for the angle is usually taken to be the direction in which maximum power is radiated, often called the boresight of the antenna. Thus for a transmitter with output Pt watt driving a lossless antenna with gain G , the flux density in the direction t of the antenna boresight at distance R meter is 22F = P G/4,R Watts/m tt The product PG is often called the effective isotropically radiated power or EIRP, and tt it describes the combination of transmitter and antenna in terms of an equivalent isotropic source with power PG Watt, radiating uniformly in all directions. tt 43 Footprint : The geographic area towards which a Satellite down link antenna directs its signal. The measure of strength of this footprint is the EIRP. Downlink frequency allocations : The ITU has split the world up into three reigons. The approximate frequency allocations above 10GHz are as follows : Region 1 : Europe, CIS, Africa and Middle East Fixed satellite service (FSS) band 10.70 - 11.70 GHz 12.50 - 12.75 GHz 17.70 - 21.20 GHz Direct broadcast service (DBS) 11.70 - 12.50 GHz Broadcast Satellite service (BSS) 11.70 - 12.50 GHz (from 2007) Region 2 : The America, and Greenland Fixed satellite service (FSS) band 11.70 - 12.20 GHz 17.70 - 21.70 GHz Direct broadcast service (DBS) 12.20 - 12.70 GHz Broadcast Satellite service (BSS) 17.30 - 17.80 GHz (from 2007) Region 3 : India, Asia, Australia and the pacific Fixed satellite service (FSS) band 11.70 - 12.75 GHz 17.70 - 21.20 GHz Direct broadcast service (DBS) 11.70 - 12.75 GHz Broadcast Satellite service (DBS) 21.40 - 22.00 GHz (from 2007) 44 Glossary of Satellite Communication Terms A/B Switch : A switch that selects one of two inputs (A or B) for routing to a common output while providing adequate isolation between the two signals. AFC (Automatic Frequency Control) : A circuit which locks an electronic component onto a chosen frequency. AGC (Automatic Gain Control) : A circuit that uses feedback to maintain the output of an electronic component at a constant level Absolute Zero : The coldest possible temperature at which all molecular motion ceases. It is expressed in degrees Kelvin as measured from absolute zero. Zero degrees Kelvin equals minus 273.168:C . Adjacent Channel : An adjacent channel is immediately next to another channel in frequency. For example, NTSC channels 5 and 6 as well as Band 9 are adjacent However channels 4 and 5 per channels 6 and 7 are separated by signals used by non-TV media. Agile Receiver : A Satellite receiver which can be tuned to any desired channel. Alignment : The process of fine tuning a dish or an electronic circuit to maximize its sensitivity and signal receiving capability. Ambient Temperature : The existing dry bulb temperature. Azimuth : A compass bearing expressed in degrees of rotation clockwise from true north. It is one of the two coordinates (azimuth and elevation) used to align a Satellite antenna. Back Match : The matching of the resistive values of the input and output of electronic devices to reduce signal reflection and ghosting. Also known as impedance matching. Back Porch : That portion of the horizontal blanking pulse that follows the trailing edge of the horizontal sync pulse. Band : A range of frequencies 45 Band Separator : A device that splits a group of specified frequencies into two or more bands. Common types include UHF/NHF, Hi/Lo-band and FM separators. This device is essentially a set of filters. Band pass Filter : A circuit or device that allows only a specified range of frequencies to pass from input to output. Bandwidth : The frequency range allocated to any communication Circuit. Base band : The raw audio and video signals prior to modulation and broadcasting. Most Satellite head end equipment utilizes base band inputs. More exactly, the composite undamped, non-deemphasized and unfiltered receiver output. This signal contains the complete set of FM modulated audio and data sub carriers. Beam width : A measure used to describe the width of vision of an antenna. Beam width is measured as degrees between the 3 dB half power points. Bird : Jargon or nickname for communication Satellites. Blanking Pulse Level : The reference level for video signals. The blanking pulses must be aligned at the input to the picture tube. Blanking Signal : Pulses used to extinguish the scan illumination during horizontal and vertical retrace periods. Block Down conversion : The process of lowering the entire band of frequencies in one step to some intermediate range to be processed inside a Satellite receiver. Multiple block down conversion receivers are capable of independently? selecting channels because each can process the entire block of signals. BNC Connector : A weather proof twist locks coax connector standard on commercial video equipment and used on some brands of Satellite receivers. Bore sight : The direction along the principle axis of either a transmitting or a receiving antenna. 46 Board band : A device that processes a signal(s) spanning a relatively broad range of input frequencies. Buttonhook Feed : A rod shaped like a question mark supporting the feed horn and LNA. A button hook feed for use with commercial grade antennas is often a hollow waveguide that directs signals from a feed horn to an LNA behind the antenna. CATV : An abbreviation for Community Antenna Television another name for cable TV. CCD : Charge coupled device. In this device charge is stored on a capacitor which is etched onto a chip. A number of samples can be simultaneously stored. Used in MAC transmissions for temporarily storing video signals. C-Band : The 3.7 to 4.2 GHz band of frequencies at which some broadcast Satellites operate. Carrier : A pure-frequency signal that is modulated to carry information. In the process of modulation it is spread out over a wider band. The carrier frequency is the center frequency on any television channel. Carrier-to-Noise Ratio (CNR) : The ratio of the received carrier power to the noise power in a given bandwidth expressed in decibels. The CNR is an indicator of how well an earth receiving station will perform in a particular location, and is calculated from Satellite power levels, antenna gain and the combined antenna and LNA noise temperature. CASS grain Feed System : An antenna feed design that includes a primary reflector, the dish, and a secondary reflector which redirects microwaves via a wave guide to a low noise amplifier. Chrominance : The hue and saturation of a color. The chrominance signal is modulated onto a 4.43 MHz carrier in the PAL television system and a 3.58 MHz carrier in the NTSC television system. Chrominance Signal : The color component of the composite base band video signal assembled from the I and Q portions. Phase angle of the signal represents hue and amplitude represents color saturation. 47 Circular Polarity : Electromagnetic waves whose electric field uniformly rotates along the signal path. Broadcasts used by Intelsat and other international Satellites use circular, not horizontally or vertically polarized waves as are common in North American and European transmissions. Circularly polarized waves are used for Satellite telephony because Faraday rotation does not alter their behavior. Clamp Circuit : A circuit that removes the dispersion waveform from the down link signal. Clarke Belt : The circular orbital belt at 22,247 miles above the equator, named after the writer Arthur C. Clarke, in which Satellites travel at the same speed as the earth?s rotation. Also called the geostationary orbit. Color Bars : A test pattern of specifically colored vertical bars used as a reference to test the performance of a color television. Coaxial Cable : A cable for transmitting high frequency electrical signals with low loss. It is composed of an internal conducting wire surrounded by an insulating dielectric which is further protected by a metal shield. The impedance of coax is a product of the radius of the central conductor, the radius of the shield and the dielectric constant of the insulation. In an SMATV system, coax impedance is 75 Ohms. Color Sync Burst : A "burst" of 8 to 11 cycles in the 4.43361875 MHz (PAL) or 3.579545 MHz (NTSC) color sub carrier frequency this wave form is located on the back porch of each horizontal blanking pulse during color transmissions. It serves to synchronize the color sub carrier's oscillator with that of the transmitter in order to recreate the raw color signals. Composite Base band Signal : The complete audio and video signal without a carrier wave. Satellite signals have audio base band information ranging in frequency from zero to 3400 Hertz. NTSC video base band is from zero to 4.2 MHz. PAL video base band ranges from 0 to 5.5 MHz. Composite Video Signal : The complete video signal consisting of the chrominance and luminance information as well as all sync and blanking pulses. 48 Companding : A form of noise reduction using compression at the transmitting end and expansion at the receiver. A compressor is an amplifier that increases its gain for lower power signals. The effect is to boost these components into a form having a smaller dynamic range. A compressed signal has a higher average level, and therefore, less apparent loudness than an uncompressed signal, even though the peaks are no higher in level. An expander reverses the effect of the compressor to restore the original signal CONE : An abbreviation for the European continent. Contrast : The ratio between the dark and light areas of a television picture. Conus : An abbreviation for the continental United States. Cross Modulation : A form of interference caused by the modulation of one carrier affecting that of another signal. It can be caused by over-loading an amplifier as well as by signal imbalances at the head end. Cross Polarization : Term to describe signals of the opposite polarity to another being transmitted and received. Cross polarization discrimination refers to the ability of a feed to detect one polarity and reject the signals having the opposite sense of polarity. Cross talk : Interference between adjacent channels often caused by cross modulation. Leakage can occur between two wires, PCB tracks or parallel cables. DC Power Block : A device which stops the flow of DC power but permits passage of higher frequency AC signals. Decibel (dB) : The logarithmic ratio of power levels used to indicate gains or losses of signals. Decibels relative to one Watts, milliWatts and millivolt are abbreviated as dBW, dBM and dBmV, respectively. Zero dBmV is used as the standard reference for all SMATV calculations. Declination Offset Angle : The adjustment angle of a polar mount between the polar axis and the plane of a Satellite antenna used to aim at the geosynchronous arc. Declination increases from zero with latitude away from the equator. Decoder : A circuit that restores a signal to its original form after it has been assuaged. 49 De-emphasis : A reduction of the higher frequency portions of an FM signal used to neutralize the effects of pre-emphasis. When combined with the correct level of pre-emphasis, it reduces over all noise levels and therefore increases the signal-to-noise ratio. Demodulator : A device which extracts the base band signal from the transmitted carrier wave. Detent Tuning : Tuning into a Satellite channel by selecting a preset resistance. Digital : Describes a system or device in which information is transferred by electrical „on-off?, high-low, or 1/0. pulses instead of continuously varying signals or states as in an analog Message. Digital-to-Analog Converter : A circuit that converts digital signals into their equivalent analog form. Direct Broadcast Satellite (DBS) : A term commonly used to describe Ku-band broadcasts via Satellite directly to individual end-users. The DBS band ranges from 11.7 to 12.2 GHz. Dish : Jargon for a parabolic microwave antenna. Distribution System : A communication system consisting of coax but occasionally of line-of-sight microwave links that carries signals from the head end to end-users. Domsat : Abbreviation for domestic communication Satellite. Down converter : A circuit that lowers the high frequency signal to a lower, intermediate range. There are three distinct types of down conversion used in Satellite receivers; single down conversion; dual down conversion; and block down conversion. Down link Antenna : The antenna on-board a Satellite which relays signals back to earth. Drifting : An instability in a preset voltage, frequency or other electronic circuit parameter. Dual-Band Feed horn : A feed horn which can simultaneously receive two different bands, typically the C and Ku-bands. 50 Earth Station : A complete Satellite receiving or transmitting station including the antenna, electronics and all associated equipment necessary to receive or transmit Satellite signals. Also known as a ground station. Effective Isotropic Radiated Power (EIRP) : A measure of the signal strength that a Satellite transmits towards the earth below. The EIRP is highest at the center of the beam and decreases at angles away from the bore sight. Elevation Angle : The vertical angle measured from the horizon up to a targeted Satellite. Energy Dispersal : The modulation of an uplink carrier with a triangular waveform. This technique disperses the carrier energy over a wider band width than otherwise would be the case in order to limit the maximum energy compared to that transmitted by an unclamped carrier. This triangular waveform is removed by a clamp circuit in a Satellite receiver. Equalizing Pulses : A series of six pulses occurring before and after the serrated vertical sync pulse to ensure proper interlacing. The equalizing pulses are inserted at twice the horizontal scanning frequency. F–connector : A standard RF connector used to link coax cables with electronic devices. FCC : The Federal Communications Commission, the regulatory board which sets standards for communications within the United States. F/D Ratio : The ratio of an antenna?s focal length to diameter. It describes antenna “depth”. Feed horn : A device that collects microwave signals reflected from the surface of an antenna. It?s mounted at the focus of all prime focus parabolic antennas. Field : One half of a complete TV picture or frame, composed of 262.5 scanning lines. There are 60 fields per second for black/white and 59.94 fields per second for color TV in NTSC transmission. In the PAL broadcast system there are 50 fields per second. Filter : A device used to reject all but a specified range of frequencies. A band pass filter allows only those signals within a given band to be communicated. A rejection filter, the 51 mirror image of a band pass filter, eliminates those signals within a specified band but passes all other frequencies. Focal Length : The distance from the reflective surface of a parabola to the point at which incoming Satellite signals are focused, the focal point. Footprint : The geographic area towards which a Satellite down link antenna directs its signal. The measure of strength of this foot-print is the EIRP. Forward Error Correction : FEC is a technique for improving the accuracy of data transmission. Excess bits are included in the out-going data stream so that error correction algorithms can be applied upon reception. Frame : One complete TV picture, composed of two fields and a total of 525 and 625 scanning lines in NTSC and PAL systems, respectively. Frequency : The number of vibrations per second of an electrical or electromagnetic signal expressed in cycles per second or Hertz. Front Porch : The portion of the horizontal blanking pulse that precedes the horizontal sync pulse. Gain : The amount of amplification of input to output power often expressed as a multiplicative factor or in decibels. Gain-to-Noise Temperature Ratio (G/T) : The figure of merit of an antenna and LNA. The higher the G/T, the better the reception capabilities of an earth station. Geostationary Orbit : See Clarke Belt Giga Hertz (GHz) : 1000 MHz or one billion cycles per second. Global Beam : A foot print pattern used by communication Satellites targeting nearly 40% of the earth's surface below. Many Intelsat Satellites use global beams. 52 Ground Noise : Unwanted microwave signals generated from the warm ground and detected by a dish. Hall Effect Sensor : A semiconductor device in which an output voltage is generated in response to the intensity of a magnetic field applied to a wire. In an actuator, the varying magnetic field is produced by the rotation of a permanent magnet past a thin wire. The pulses generated serve to count the number of rotations of the motor. Hard-Line : A low-loss coaxial cable that has a continuous hard metal shield instead of a conductive braid around the outer perimeter. This type of cable was used in the pioneer days of Satellite television. Head end : The portion of an SMA TV system where all desired signals are received and processed for subsequent distribution. Heliax : A thick low-loss cable used at high frequencies; also known as hard-line. Hertz : An abbreviation for the frequency measurement of one cycle per second. Named after Heinrich Hertz, the German Scientist who first described the properties of radio waves. High Definition Television (HDTV) : An innovative television format having approximately twice the number of scan lines in order to improve picture resolution and viewing quality. High Power Amplifier (HPA): An amplifier used to amplify the uplink signal. Horizontal Blanking Pulse : The pulse that occurs between each horizontal scan line and extinguishes the beam illumination during the retrace period. Horizontal Sync Pulse : A 5.08 microsecond (4.7 microsecond in the PAL system) rectangular pulse riding on top of each horizontal blanking pulse. It synchronizes the horizontal scanning at the television set with that of the television camera. Hum Bars : A form of interference seen as horizontal bars or black regions passing across the field of a television screen. . I Signal : 53 One of the two color video signals which modulate the color subcarrier. It represents those colors ranging from reddish orange to cyan. Impulse pay-per-view (IPPV) is a feature of a decoder that allows an authorized subscriber to purchase a one-time scrambled program at will IPPV shows are selected by a button on the decoder or its remote control unit. Inclinometer : An instrument used to measure the angle of elevation to a Satellite from the surface of the earth. Interference : An undesired signal intercepted by a TVRO that causes video and/or audio distortion. Insertion Loss : The amount of signal energy lost when a device is inserted into a communication line. Also known as “feed through” loss. Interlaced Scanning : A scanning technique to minimize picture flicker while conserving channel band width. Even and odd numbered lines are scanned in separate fields both of which when combined paint one frame or complete picture. Intermediate Frequency (IF) : A middle range frequency generated after down conversion in any electronic circuitry including a Satellite receiver. The majority of all signal amplification, processing and filtering in a receiver occur in the IF range. INTELSAT : The International Telecommunication Satellite Consortium, a body of 154 countries working towards a common goal of improved worldwide Satellite communications. Isolator : A device that allows signals to pass unobstructed in one direction but which attenuates their strength in the reverse direction. Isolation Loss : The amount of signal energy lost between two ports of a device. An example is the loss between the feed through port and the tap/drop of a top-off device. Kelvin Degrees (:K) : The temperature above absolute zero, the temperature at which all molecular motion stops, graduated in units the same size as degrees Celsius(:C). Absolute zero equals-273?C or 459?F. 54 Kilohertz (KHz) : One thousand cycles per second. Ku-Band : The microwave frequency band between approximately 11 and 13 GHz used in Satellite broadcasting. Latitude : The measurement of a position on the surface of the earth north or south of the equator measured in degrees of angle. Line Amplifier : An amplifier in a transmission line that boosts the strength of a signal. Line Splitter : An active or passive device that divides a signal into two or more signals containing all the original information. A passive splitter feeds an attenuated version of the input signal to the output ports. An active splitter amplifies the input signal to overcome the splitter loss. Local Oscillator : A device used to supply a stable single frequency to an Up converter or a down -converter. The local oscillator signal is mixed with the carrier wave to change its frequency. Longitude : The distance in degrees east or west of the prime meridian, located at zero degrees. Low Noise Amplifier (LNA) : A device that receives and amplifies the weak Satellite signal reflected by an antenna via a feed horn. C-band LNAs typically have their noise characteristics quoted as noise temperatures rated in degrees Kelvin. K-band LNA noise characteristics are usually expressed as a noise figure in decibels. Low Noise Block Down converter (LNB) : A low noise microwave amplifier and converter which down converts a block or range of frequencies at once to an intermediate frequency range, typically 950 to 1450 MHz or 950 to 1750 MHz. Low Noise Converter (LNC) : An LNA and a conventional down converter housed in one weather proof box. This device converts one channel at a time. Channel selection is controlled by the Satellite receiver. The typical IF for LNCs is 70 MHz. Magnetic Variation : The difference between true north and the north indication of a compass. 55 Master Antenna TV (MATV) : Broadcast receiving stations that use one or more high-quality centrally located UHF and/or VHF antennas which relay their signals to many televisions in a local apartment/condo or group-housing complex. Match : The condition that exists when 100 percent of available power is transmitted from one device to another without any losses due to reflections. Matching Transformer : A device used to match impedance between devices. A matching transformer is used, for example, when connecting a 75 , coax to a television 300 , input terminal. Mega Hertz (MHz) : One millions cycles per second. Microprocessor : The central processing unit of a computer or control system, either on a single integrated circuit chip (IC) or on several ICs. Microwave : The frequency range from approximately 1 to 30 GHz and above. Mixer : A device used to combine signals together. Modulation : A process in which a message is added or encoded onto a carrier wave. Among other methods, this can be accomplished by frequency or amplitude modulation, known as AM or FM, respectively. Monochrome : A black and white television picture. Mount : The structure that supports earth station antenna. Polar and az el mounts are the most common variety. Multiple Analog Component (MAC) Transmissions : An innovative television transmission method which separates the data, chrominance and luminance components and compresses them for sequential relay over one television scan line. There are a number of systems in use and under development including A-MAC, BMAC, C-MAC, D-MAC, D2-MAC, E-MAC and F-MAC. 56 Multiplexing : The simultaneous transmission of two or more signals over a single communication channel. The interleaving of the luminance and chrominance signals is one form of multiplexing, known as frequency multiplexing. MAC transmissions make use of time division multiplexing. N-Connector : A low-loss coaxial cable connector used at the elevated C-band microwave frequencies. NTSC : The National Television Standards Committee which created the standard for North American TV broadcasts. NTSC Color Bar Pattern : The standard test pattern of six adjacent color bars including the three primary colors plus their three complementary shades. Negative Picture Phase : Positioning the composite video signal so that the maximum level of the sync pulses is at 100% amplitude. The brightest picture signals are in the opposite negative direction. Negative Picture Transmission : Transmission system used in North America and other countries in which a decrease in illumination of the original scene causes an increase in percentage of modulation of the picture carrier. When demodulated, signals with a higher modulation percentage have more positive voltages. Noise : An unwanted signal which interferes with reception of the desired information. Noise is often expressed in degrees Kelvin or in decibels. Noise figure : The ratio of the actual noise power generated at the input of an amplifier to that which would be generated in an ideal resistor. The lower the noise figure the better the performance. Noise Temperature : A measure of the amount of thermal noise present in a System or a device. The lower the noise temperature, the better the performance. Odd Field : The half frame of a television scan which is composed of the odd numbered lines. Offset Feed : A feed which is offset from the center of a reflector for use in Satellite receiving systems. This configuration does not block the antenna aperture. 57 Orthomode Coupler : A wave guide, generally a three-port device, that allows simultaneous reception of vertically and horizontally polarized signals. The input port is typically a circular wave guide. The two output ports are rectangular waveguides. PAL : Phase Alternate Line. The European color TV format which evolved from the American NTSC standard. Pad : A concrete base upon which a supporting pole and antenna can be mounted. Path Loss : The attenuation that a signal under goes in traveling over a path between two points. Path loss varies inversely as the square of the distance traveled. Parabola : The geometric shape that has the property of reflecting all signals parallel to its axis to one point, the focal point. Pay-Per-View : Pay-per-view is a method of purchasing programming on a per-program basis. Persistence of Vision : The physiological phenomena whereby a human eye retains perception of an image for a short time after the image is no longer visible. Phase : A measure of the relative position of a signal relative to a reference expressed in degrees. Phase Distortion : A distortion of the phase component of a signal. This occurs when the phase shift of an amplifier is not proportional to frequency over the design bandwidth. Picture Detail : The number of picture elements resolved on a television picture screen. More "crisp" pictures result as the number of picture elements is increased. Polar Mount : An antenna mount that permits all Satellites in the geosynchronous are to be scanned with movement of only one axis. Polarization : A characteristic of the electromagnetic wave. Four senses of polarization are used In Satellite transmissions: horizontal; vertical; right-hand circular, and left-hand circular. 58 Positive Picture Phase : Positioning of the composite video signal so that the maximum point of the sync pulses is r at zero voltage. The brightest illumination is caused by the most positive voltages. Preamplifier : The first amplification stage. In an SMA TV system, it is the amplifier mounted adjacent to an antenna to increase a weak signal prior to its processing at the head end. Pre-emphasis : Increases in the higher frequency components of an FM signal before transmission. Used in conjunction with the proper amount of de-emphasis at the receiver, it results in combating the higher noise detected in FM transmissions. PSD : An abbreviation for polarity selection device. Primary Colors : Red, green and blue. Prime Focus Antenna : A parabolic dish having the feed/LNA assembly at the focal point directly in the front of the antenna. Q Signal : One of two color video signal components used to modulate the color subcarrier. It represents the color range from yellowish to green to magenta. Radio Frequency : The approximately 10 KHz to 100 GHz electromagnetic band of frequencies used for manmade communication. Raster : The random pattern of illumination seen on a television screen when no video signal is present. Reed Switch : A mechanical switch which uses two thin slivers of metal in a glass tube to make and break electrical contact and thus to count pulses which are sent to the antenna actuator controller. The position of the slivers of metal is governed by a magnetic field applied by a bar or other type of magnet. Reference Signal : A highly stable signal used as a standard against which other variable signals may be compared and adjusted. Return Loss : 59 A ratio of the amount of reflected signal to the total available signal entering a device expressed in decibels. Retrace : The blanked-out line traced by the scanning beam of a picture tube as it travels from the end of any horizontal line to the beginning of either the next horizontal line or field. SAW (Surface Acoustic Wave) Filter : A solid state filter that yields a sharp transition between regions of transmitted and attenuated frequencies. Satellite Receiver : The indoors electronic component of an earth station which down converts, processes and prepares Satellite signals for viewing or listening. Scanning : The organized process of moving the electron beam in a television picture tube so an entire scene is drawn as a sequential series of horizontal lines connected by horizontal and vertical retraces. Scrambling : A method of altering the identity of a video or audio signal in order to prevent its reception by persons not having authorized decoders. Screening : A metal, concrete or natural material that screens out un-wanted Tl from entering an antenna or a metal shield that prevents the ingress of unwanted RF signals in an electronic circuit. Serrated Vertical Pulse : The television vertical sync pulse which is subdivided into six serrations. These sub-pulses occur at twice the horizontal scanning frequency. Servo Hunting : An oscillatory searching of the feed horn probe when use of inadequate gauge control cables results in insufficient voltage at the feed horn. Side Lobe : A parameter used to describe an antenna's ability to detect off-axis signals. The larger the side lobes, the more noise and interference an antenna can detect. Single Channel Per Carrier (SCPC) : A Satellite transmission system that employs a separate carrier for each channel, as opposed to frequency division multiplexing that combines many channels on a single carrier. Signal-to-Noise Ratio (SNR) : 60 The ratio of signal power to noise power in a specified bandwidth, usually expressed in decibels. Skew : A term used to describe the adjustment necessary to fine tune the feed horn polarity detector when scanning between Satellites. Slant Range : The distance that a signal travels from a Satellite to a TVRO Snow : Video noise or sparklies caused by an insufficient signal-to-noise input ratio to a television set or monitor. Solar Outage : The loss of reception that occurs when the sun is positioned directly behind a target Satellite. When this occurs, solar noise drowns out the Satellite signal and reception is lost. Sparkles : Small black and/or white dashes in a television picture indicating an insufficient signal-to noise ratio. Also known as "snow". Spherical Antenna : An antenna system using a section of a spherical reflector to focus one or more Satellite signals to one or a series of focal areas. Splitter : A device that takes a signal and splits it into two to more identical but lower power signals. Subcarrier : A signal that is transmitted within the bandwidth of a stronger signal. In Satellite transmissions a 6.8 MHz audio sub carner is often used to modulate the C-band carrier. In television, a 3.58 MHz subcarrier modulates the video carrier on each channel. Surface Acoustic Wave : A sound or acoustic wave traveling on the surface of the optically polished surface of a piezoelectric material. This wave travels at the speed of sound but can pass frequencies as high as several gigahertz. See SAW Filter. Synchronizing Pulses : Pulses imposed on the composite base band video signal used to keep the television picture scanning in perfect step with the scanning at the television camera. TVRO : 61 A television receive-only earth station designed only to receive but not to transmit Satellite communications. Tap : A device that channels a specific amount of energy out the main distribution system to a secondary outlet. Terrestrial Interference (TI) : Interference of earth-based microwave communications with reception of Satellite broadcasts. Tilt : The uneven attenuation of a broad band signal as it travels through a coaxial cable. In general, attenuation increase as signal frequency increases. Thermal Noise : Random, undesired electrical signals caused by molecular motion, known more familiarly as noise. Trace : The movement of the electron beam from left to right on a television screen. Threshold : A minimal signal to noise input required to allow a video receiver to deliver an acceptable picture. Transponder : A microwave repeater, which receives, amplifies, down converts and re-transmits signals at a communication Satellite. Trap : An electronic device that attenuates a selected band of frequencies in a signal. Also known as a notch filter. UHF : Ultrahigh frequencies ranging from 300 to 3,000 MHz. North American TV channels 14 through 83. European TV channels 21 to 69. Up converter : A device that increases the frequency of a transmitted signal. Up link : The earth station electronics and antenna which transmit information to a communication Satellite. VHF : 62 Very high frequencies in the range from 54 MHz to 216 MHz, NTSC TV channels 2 through 13. Very high frequency range from 30 to 300 MHz. VSWR (Voltage Standing Wave Ratio) : The ratio between the minimum and maximum voltage on a transmission line. An ideal VSWR is 1.0. Ghosting can result as the VSWR increases. It is also a measure of the percentage of reflected power to the total power impinging upon a device. Vertical Blanking Pulse : A pulse used during the vertical retrace period at the end of each scanning field to extinguish illumination from the electron beam. Vertical Sync Pulse : A series of pulses which occur during the vertical blanking interval to synchronize the scanning process at the television with that created at the audio. See also Serrated Vertical Pulse. Video Signal : That portion of the transmitted television signal containing the picture information. Voltage Tuned Oscillator (VTO) : An electronic circuit whose output oscillator frequency is adjusted by voltage. Used in down converters and Satellite receivers to select from among transponders. Video Monitor : A television that accepts unmodulated base band signals to reproduce a broadcast. 63 Experiment 1 Objective : Understanding Basic concepts of Satellite communication. Theory : Sinusoidal electromagnetic waves (E/M waves) All radio and television signals consists of electrical and magnetic fields which in free 8space travel at speed of light (approx 3 ， 10 meters/seconds), these waves consists of an Electric field (E), measured in amperes/meter, the E and H field components are always at right angle to each other and the direction of travel is always at right angles of both fields. The amplitudes vary sinusoidal as they travel through space. In fact it is impossible to produce a non sinusoidal E/M wave!(the importance of this statement will be grasped more easily when modulation is discussed.) The Sine Wave : Cycle : One complete electrical sequence Peak Value (V) : Maximum positive or negative value also called amplitude. p Period (t) : Time to complete one cycle Frequency (f) : Number of cycles per second in Hertz. (One hertz = one cycle per second). It follows that period and frequency are reciprocals of each other. T=1/f Commonly used multiplies of hertz are: 3Kilohertz (KHz) =10 Hz = 1000Hz 6Megahertz (MHz) = 10 Hz = 1000000Hz 9Gigahertz( GHz) = 10 Hz = 1000000000Hz RMS Value : This is 0.707 of the peak value and unless otherwise stated, any reference to voltage or current in technical literature is normally taken to mean this value for Example, the supply mains in UK is a sinusoidal variation, stated to be '240 Volts' so the peak value is 240/0.707 = 339 volts. Angular Velocity (w) : This is an indirect way of expressing the frequency W = 2, f rad / sec Instead of considering the no of complete cycles angular velocity is a measure of how fast the vector angle is changing. The Voltage equation of sine wave which gives the instantaneous value (v) of a sine wave at any point in the cycle is given by: v = Vsin, p 64 for a convenience and brevity, the 2,F part is often lumped together and given the title of angular velocity(,).Using this notation the equation of sine wave can be written as : v =V sin,t p Wavelength : Since E/M waves at a known velocity vary sinusodially, it is possible to consider how far a wave of given frequency (f) would travel during the execution of one cycle. Denoting the speed of light as c the wavelength (,) is given by: , = c / f From this, it so as clear that the higher the frequency the shorter the wavelength Satellite broadcasting employs waves in this order of 10GHz frequency so the order of wavelength can be calculated as follows: 89, = (3 ， 10) / (10 ， 10) -2, = 3 ， 10m = 3 cm. In practice the frequencies used are not necessarily a nice round figure like 10 GHz Nevertheless, the wavelength in present use invariably works out in terms of centimeters. The enormously high frequencies are used in satellite broadcasting? Before this can be answered it is necessary to understand some fundamentals laws to broadcasting of information, whether it be sound or picture information. Carrier frequency : For simplicity, assume that it is required to transmit through space a 1000Hz audio signal, in theory an electrical oscillator and amplifier could be rigged up and tuned to 1000 cycles per sec. And the output fed to a piece of wire acting as primitive aerial. It is an unfortunate fact of nature that of nature that for reasonably efficient radiation a wire aerial should have a length some where in order of wavelength of 1000 Hz using the equation given above : 835, = c / f = 3 ， 10 / 10 = 3 ， 10 meters. , = 300000 m which is about 188 miles. Apart from the sheer impractically of such an aerial, waves at these low frequencies suffer severe attenuation due to ground absorption. Another important reason for using high frequencies is due to the considerations of bandwidth, which is treated later. This solution is to use a high frequency wave to carry the signal but allow the Intelligence (the 1000 Hz in our example) to modify one or more of its characteristics. The high frequency wave is referred to as the carrier (F) simply because it carries the c information in some way the method of impressing this low frequency information on to carrier is called modulation. There are two main type?s amplitude modulation (AM) and frequency modulation (FM) 65 Amplitude modulation : The low frequency modulating signal is made to alter the amplitude of carrier at the transmitter before the composite waveform is sent to the aerial system. If the amplitude of the modulating signal causes the carrier amplitude to vary between double its unmodulated height and zero, the modulation is said to be 100 percent. terrible distortion results if the modulation amplitude is ever allowed to exceed 100 percent. Modulation factor : This is the ratio of modulation amplitude (V) to carrier amplitude (V) mc m = V / V mc When m = 1 the modulation is 100 percent, although 100 percent is an advantage it is too dangerous in practice, due to the possibility of over modulation, so 80% (m = 0.8) is normally considered the safe limit. Sidebands : Although the modulating signal is simple sinusoidal waveforms, in practice it will be more complex. Thus the envelope of the waveform will be non-sinusoidal. The un-modulated carrier sine wave has the instantaneous form: v = V sin,t pc But the amplitude of this wave (V) is made to vary by the modulating frequency which p causes V to have the form : p V = V sin,t pm Substituting this expression in the first equation gives : v = Vsin,t. sin,t mcc We know one of the trigonometric identities Sin A Sin B= ? Cos (A,B), ? Cos (A+B) So it follows that the modulated carrier waveform splits up in space into three pure Sinusoidal components : 4. The carrier frequency 5. The frequency equal to the sum of the carrier and modulating frequencies. This is called Upper sideband. 6. The frequency equal to the difference of the carrier and modulating frequencies. This is called lower sideband. If the carrier frequency is 1000000 Hz and the modulating frequency is 1000 Hz then the upper sideband is 1001000 Hz sine wave and lower sideband is 999000 Hz. In practice the modulating frequency will seldom be anything as simple as a 1000 Hz sine wave but more probably, may consists of speech or picture information which contains a complex mixture of frequencies. For example, the music frequency extends from about 20 Hz to about 18 KHz so, to transmit high quality sound the upper sidebands 66 would have to contain spread of frequencies extending from 20 Hz to 18 KHz above the carrier and the lower sidebands frequencies extending 20 Hz to 18 KHz below the carrier. Television transmission is more difficult because picture have a far greater information content than sound. Wider the sidebands of transmission, greater space will occupy in the frequency spectrum so broadcast stations geographically close together must operate on frequencies well away from each other in order to prevent the interference from their respective sidebands. Since television station occupy several MHz in the spectrum, carrier frequencies are forced into ever higher and higher frequencies as the number of stations fight for space. there are several novel solutions to the overcrowding problem for example it is not essential to transmit both sidebands since all the required information is contained in one of then, providing of course the carrier is sent with it. Such transmission is contained in one of them, providing of course the carrier is sent with it. Such transmissions are called SSB (single sideband). An even more drastic curtailment is to reduce the carrier at the transmitter to almost zero and use it to synchronize a locally generated carrier at the receiving end a Technique known as single sideband vestigial carrier modulation. Frequency Modulation : Where as amplitude modulation alters the envelope in the vertical plane, frequency modulation takes place in the horizontal plane, the amplitude of the carrier is kept constant but the frequency is caused to deviate proportional to the modulating amplitude. Frequency Deviation : The maximum amount by which the carrier frequency is increased or decreased by the modulating amplitude is called the frequency deviation. It depends up on the amplitude (peak value) of the modulating voltage. In the case satellite broadcasting, the signal beamed down to earth has a typical frequency deviation of about 16 MHZ and the bandwidth occupied by the picture information is commonly about 27 MHz. Modulation index : This is the ratio of the frequency deviation (,f) to the highest modulating frequency (f) m M =,f / fm In contrast with amplitude modulation, the modulation index is not necessarily restricted to maximum of unity. 67 Pre-emphasis (de-emphasis) improvement : Since the noise power density of a receiver demodulator output increases with frequency, high frequencies are boosted or pre-emphasized prior to transmission, when the signal is subsequently demodulated in the receiver the signal and its acquired noise is deemphasized or reduced by an equal amount the overall effect is to reduce the noise component and leads to typical improvement in S/N of 2dB for PAL I signals or 2.5 dB for NTSC M signals. Noise : An unwanted signal which interferes with reception of the desired information. Noise is often expressed in degrees Kelvin or in decibels. Decibel (dB) : The logarithmic ratio of power levels used to indicate gains or losses of signals. Decibels relative to one Watts, milliWatts and millivolt are abbreviated as dBW, dBM and dBmV, respectively. Zero dBmV is used as the standard reference for all SMATV calculations. dB =10 log P/ P 12 The sign of result is positive if p is greater than p and negative if p is less than p. 1212 Voltage db: Although dbs are normally used in conjunction with power ratio, it is sometimes convenient to express voltage ratio in db terms. dB = 20 log v / v 12 The use of 20 instead of 10 is because power is proportional to the square of the voltage so the constant is 20 instead of 10. Ku-Band Satellite TV : The microwave frequency band between approximately 11 and 13 GHz used in Satellite broadcasting in European nations. Clarke Belt : The circular orbital belt at 22,247 miles above the equator, named after the writer Arthur C. Clarke, in which Satellites travel at the same speed as the earth's rotation. Also called the geostationary orbit. 68 Antenna : An antenna may be defined in the following way. To radiate or receive electromagnetic waves an antenna is required. Antenna or aerial is system of elevated conductors which couples or matches the transmitter or receiver to free space. A transmitting antenna connected to a transmitter by transmission line, forces electromagnetic waves into free space which travel in space with velocity of light. Similarly, a receiving antenna connected to a radio receiver, receives or intercepts a portion of electromagnetic waves through space. Thus radio antenna is defined as the structure associated with region of transition between a guided wave and a free space wave or between a free space wave and guided waves. The official definition of antenna according to the institution of electrical and electronics engineers is the simply a "means for radiating or receiving radio waves". A Satellite antenna intercepts the extremely weak microwave transmission from a targeted Satellite and reflects the signal to its focal point, where the feed horn is placed. This is the process that concentrates the signal so that the necessary power is available for subsequent electronic components. The quality of a Satellite antenna, often simply called a dish, is determined by how well it targets a Satellite and concentrates the desired signal and by how well it ignores unwanted noise and interference. Dishes must be durable and able to withstand winds as well as other natural and man-made forces. In order to be able to compete in the marketplace, they also must be aesthetically pleasing and affordably priced. Dish Antenna : To receive signal from the Satellite dish antenna are used. They are parabolic in shape. A dish antenna collects the signal coming from the Satellite & focuses it at a point known as Focal point. Dish antenna is used to obtain VHF & UHF signals. For different frequency ranges different sizes of dish antenna are used. The size of dish antenna depends on wave length of the signal. For UHF range the size of the dish antenna is 3 to 5 m & for signal up to 12 GHz the size is 91 to 180 cm. These are made of fiber glass. The reflector at the dish antenna is made up of aluminum or fiber glass. For different frequency the depth of the dish antenna is also different. Feed Horn : A dish antenna receives the signal coming through a very large area, these get reflected to a point, at that point a pipe type instrument is fitted. This pipe type instrument is known as Feed Horn. From the feed horn the signals are given to LNB. It is made in such a way that it can receive maximum signal on adjustment. It is adjusted on the basis of picture & sound quality reception. It acts as impedance matching amplifier. 69 Low Noise Block (Down Converter) : Most important part mounted on the disk antenna is LNB. The signal from the feed horn is fed to LNB. These are of SHF range & contain unwanted frequencies. This high frequency cannot be fed directly to TV. Theoretically LNB converts high frequency range to low frequency range & also removes noise. In Satellite reception different LNB are used for different frequency ranges. There is a high frequency amplifier in LNB to amplify the faded signals coming from the Satellite. Now this signal is converted into low frequency of definite amount. There is a high frequency local oscillator & mixer inside a LNB. The amplified signal from the amplifier and the signal from the local oscillator come to the mixer sections just like that in the normal tuner. The LNB used for C band reception gets the input of 3.7 to 4.2 GHz & the output is 950 to 1450 MHz. The output signals are then fed to Satellite receiver through coaxial cables. Satellite Receiver: The purpose of Satellite receiver is the selection of channel for listening, viewing, or both and transforming the signals in to a form suitable for input to domestic TV and stereo equipment. Various subsections of Satellite Receiver. 7. Power supply 8. Down conversion and tuner circuit 9. Final IF stage 10. FM video demodulator 11. Video Processing Stages 12. Audio processing stages Effective isotropic radiated power (EIRP) and foot print maps it the calculation of the power received by an earth station from a Satellite transmitters fundamental to the understanding of Satellite communications. Consider a transmitting source, in free space, radiating a total power P, Watts uniformly in all directions called an isotropic t source. At a distance R from the hypothetical isotropic source, the flux density crossing the surface of a sphere, radius R, is given by ,2F = P /,,R Watts/m t In practice we use directive antennas to constrain out transmitted power to be radiated primarily in one direction. The antenna has a gain G (6) in a direction 6, defined as the ratio of power per unit solid angle radiated in a given direction to the average power radiated per unit solid angle: G (,) = P (,)/ (P/4,) 0 Where P (,) is the power radiated per unit solid angle by the test antenna G (,) is the gain of the antenna at an angle 70 The reference for the angle is usually taken to be the direction in which maximum power is radiated, often called the boresight of the antenna. Thus for a transmitter with output Pt Watts driving a lossless antenna with gain G, the flux density in the direction t of the antenna boresight at distance R meter is ,2F = P G/,,R Watts/m tt The product PG is often called the effective isotropically radiated power or EIRP, and tt it describes the combination of transmitter and antenna in terms of an equivalent isotropic source with power PG Watts, radiating uniformly in all directions. tt Footprint : The geographic area towards which a Satellite down link antenna directs its signal. The measure of strength of this footprint is the EIRP. Downlink frequency allocations : The ITU has split the world up into three regions. The approximate frequency allocations above 10 GHz are as follows : Region 1 : Europe, CIS, Africa and Middle East Fixed satellite service (FSS) band 10.70 - 11.70 GHz 12.50 - 12.75 GHz 17.70 - 21.20 GHz Direct broadcast service (DBS) 11.70 - 12.50 GHz Broadcast Satellite service (BSS) 11.70 - 12.50 GHz (from 2007) Region 2 : The America, and Greenland Fixed satellite service (FSS) band 11.70 - 12.20 GHz 17.70 - 21.70 GHz Direct broadcast service (DBS) 12.20 - 12.70 GHz Broadcast Satellite service (BSS) 17.30 - 17.80 GHz (from 2007) Region 3 : India, Asia, Australia and the pacific Fixed satellite service (FSS) band 11.70 - 12.75 GHz 17.70 - 21.20 GHz Direct broadcast service (DBS) 11.70 - 12.75 GHz Broadcast Satellite service (DBS) 21.40 - 22.00 GHz (from 2007) 71 Experiment 2 Objective : Establishing a direct communication link between Uplink Transmitter and Down link Receiver using tone signal. Equipments Needed : 1. Uplink Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. Procedure : 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter and frequency display will come on. 3. The transmitting frequency can be selected by frequency selection switch. The frequency can be changed from 2450-2468 MHz. 4. The transmitter „On-Off? toggle switch will switch „On – Off? the transmission. 5. Connect X1 Antenna to Uplink transmitter with BNC -BNC lead. 6. Set the output gain of Uplink transmitter to maximum. 7. Place Downlink Receiver at a convenient distance of 5- 7m. (It can go even up to 10m.). 8. Connect the Downlink Receiver to the AC Mains and switch it „On? by mains switch. 9. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. 10. The Downlink receiver „On-Off? toggle switch will switch „On-Off' the receiver. 11. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 12. Align both the Transmitter and Receiver Antenna's in line. 13. Keep the uplink transmitter and downlink receiver frequency to the same frequency. 14. Now connect Tone out signal to Tone input of the Uplink transmitter by patch cord. 15. Keep Downlink receiver voice switch in the „On? position and you will be able to hear tone in the speaker of receiver. 16. This is a test link for direct communication between transmitter and receiver. 17. Connect any other audio signal to the Audio II of Uplink transmitter and you will hear the music in the speaker of Downlink Receiver. Result : A clear music indicates that the microwave link has been successfully setup between uplink transmitter and down link receiver directly. 72 Experiment 3 Objective : Setting up an Active satellite link and demonstrate Link Fail operations. Equipments Needed : 1. Uplink Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. 5. Satellite Transponder (Trans-Receiver) Theory : The Uplink Transmitter sends signals at an Uplink frequency, which is higher than downlink frequency to avoid the interference. The quality of signal is much improved with active satellite especially when distances between transmitter and receiver are considerable. Procedure : 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter and frequency display will come on. 3. The transmitting frequency can be selected by Frequency Selection switch. The frequency can be changed from 2450-2468 MHz. 4. The transmitter „On-Off? toggle switch will switch „On – Off? the transmission. 5. Connect X1 Antenna to Uplink transmitter with BNC -BNC lead. 6. Set the OUTPUT gain of Uplink transmitter to maximum. 7. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). 8. Connect the Downlink Receiver to the AC Mains and switch it „On? by mains switch. 9. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. 10. The Downlink receiver „On-Off? toggle switch will switch „On-Off? the receiver. 11. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 12. Align both the Transmitter and Receiver Antenna's in line. 13. Place a Satellite Transponder between Transmitter and Receiver at a convenient distance; preferably all three can be placed in equidistant triangle of distance 5-7m. 14. Connect the Satellite Transponder to the AC Mains and switch it ON by mains switch. 73 15. The Receiver side of Satellite Transponder has an „On-Off? toggle switch, which will switch „Off? the receiver of satellite. Similarly „On-Off? toggle Switch „On? Transmitter side will switch „Off? transmitter of satellite. 16. Adjust transmitter uplink frequency to 2468 MHz and Transponder receiver frequency also to 2468 MHz. In actual satellite transponder the multiplexer and demultiplexer are provided which continuously keeps on receiving the input frequency's in the satellite and transmit different 'output frequency. Here we do this procedure manually to understand the operations of change in frequencies in the satellite. We have three uplink frequencies and three downlink frequencies and we can demonstrate manually how an actual satellite works. 17. Keep Downlink Frequency of Transponder to 2414 MHz. 18. Keep the Downlink Receiver to 2414 MHz. 19. Now connect a tone output to Tone input of the Uplink transmitter by patch cord. 20. Keep Downlink receiver voice switch in the „On? position and you will be able to hear tone in the speaker of receiver. 21. This is a test link for Active Satellite communication. 22. Connect any other audio signal to the Audio II of Uplink transmitter and you will hear the music in the speaker of Downlink Receiver. Result : The above setup shows that a successful satellite communication link has been setup between Transmitter and Receiver. Link Fail Operation : By switching „Off? the receiver and transmitter of Satellite Transponder one by one, you can demonstrate a Link Fail operation. 74 Experiment 4 Objective : Establishing an AUDIO-VIDEO satellite link between Transmitter and Receiver Equipments Needed : 1. Uplink Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. 5. Satellite Transponder (Trans-receiver) 6. AUDIO/ VIDEO input (VCD) to be connected to Uplink Transmitter 7. Monitor (TV monitor) to be connected to Downlink Receiver. Procedure : 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter and frequency display will come on. 3. The transmitting frequency can be selected by Frequency Selection switch. The frequency can be changed from 2450-2468 MHz. 4. The transmitter „On-Off? toggle switch will switch „On–Off? the transmission. 5. Connect X1 Antenna to Uplink transmitter with BNC -BNC lead. 6. Set the OUTPUT gain of Uplink transmitter to maximum. 7. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). 8. Connect the Downlink Receiver to the AC Mains and switch it ON by mains switch. 9. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. 10. The Downlink receiver „On-Off? toggle switch will switch „On–Off? the receiver. 11. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 12. Align both the Transmitter and Receiver Antenna's in line. 13. Place a Satellite Transponder between Transmitter and Receiver at a convenient distance; preferably all three can be placed in equidistant triangle of distance 5-7m. 14. Connect the Satellite Transponder to the AC Mains and switch it „On? by mains switch. 15. The Receiver side of Satellite Transponder has an „On-Off? toggle switch, which will switch „Off? the receiver of satellite. Similarly „On-Off? toggle Switch „On? Transmitter side will switch „Off? transmitter of satellite. 75 16. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency also to 2468 MHz. 17. Keep Downlink Frequency of Transponder to 2414 MHz. 18. Keep the Downlink Receiver to 2414 MHz. 19. Connect the Audio/Video signal at the input socket provided on the Uplink Transmitter, Video at video input and audio at Audio I input. 20. Connect TV monitor to the Audio/Video output of Downlink receiver. (Video from Video Output, audio from Audio I output) Set TV in AV Mode. 21. The TV monitor will display video and audio signal that you have connected to Uplink Transmitter input. Result : The monitor display shows that a successful audio and video link has been establish between Transmitter and Receiver through satellite. Try link fail by using Receiver „Off? and Transmitter „Off? switch the Transponder. 76 Experiment 5 Objective : Communicating VOICE signal through satellite link Equipments Needed : 1. Uplink. Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. 5. Satellite Transponder (Trans-receiver) 6. Active MIKE Procedure : 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter and frequency display will come on. 3. The transmitting frequency can be selected by Frequency Selection switch. The frequency can be changed from 2450-2468 MHz. 4. The transmitter „On-Off? toggle switch will switch „On–Off? the transmission. 5. Connect X1 Antenna to Uplink transmitter with BNC -BNC lead. 6. Set the OUTPUT gain of Uplink. transmitter to maximum. 7. Place Downlink. Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). 8. Connect the Downlink. Receiver to the AC Mains and switch it „On? by mains switch. 9. The Downlink. Receiver Frequency can be changed from 2414-2432 MHz. 10. The Downlink receiver „On-Off? toggle switch will switch „On–Off? the receiver. 11. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 12. Align both the Transmitter and Receiver Antenna's in line. 13. Place a Satellite Transponder between Transmitter and Receiver at a convenient distance; preferably all three can be placed in equidistant triangle of distance 5-7m. 14. Connect the Satellite Transponder to the AC Mains and switch it „On? by mains switch. 15. The Receiver side of Satellite Transponder has an „On-Off? toggle switch, which will switch „Off? the receiver of satellite. Similarly „On-Off? toggle Switch „On? Transmitter side will switch „Off? transmitter of satellite. 16. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency also to 2468 MHz. 77 17. Keep Downlink Frequency of Transponder to 2414 MHz. 18. Keep the Downlink Receiver to 2414 MHz. 19. Connect mike input at the socket marked 'MIC' on the Uplink Transmitter. 20. Connect the voice link of Uplink transmitter and Downlink receiver „On?. 21. Speak in the mike and you will hear the same sound in the speaker of receiver. Result : The above shows a successful establishment of voice link between transmitter and receiver. 78 Experiment 6 Objective : Changing different combinations of uplink and downlink frequencies and to check the communication link Equipments Needed : 1. Uplink Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. 5. Satellite Transponder (Trans-receiver) 6. Audio/Video input (VCD) to be connected to Uplink Transmitter 7. Monitor (TV monitor) to be connected to Downlink Receiver. Procedure: 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter and frequency display will come on. 3. The transmitting frequency can be selected by Frequency Selection switch. The frequency can be changed from 2450-2468 MHz. 4. The transmitter „On-Off? toggle switch will switch „On – Off? the transmission. 5. Connect X1 Antenna to Uplink transmitter with BNC -BNC lead. 6. Set the output gain of Uplink transmitter to maximum. 7. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). 8. Connect the Downlink Receiver to the AC Mains and switch it „On? by mains switch. 9. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. 10. The Downlink receiver „On-Off? toggle switch will switch „On-Off? the receiver. 11. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 12. Align both the Transmitter and Receiver Antenna's in line. 13. Place a Satellite Transponder between Transmitter and Receiver at a convenient distance; preferably all three can be placed in equidistant triangle of distance 5-7m. 14. Connect the Satellite Transponder to the AC Mains and switch it „On? by mains switch. 79 15. The Receiver side of Satellite Transponder has an „On-Off? toggle switch, which will switch „Off? the receiver of satellite. Similarly „On-Off? toggle Switch „On? Transmitter side will switch „Off? transmitter of satellite. 16. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency also to 2468 MHz 17. Keep Downlink Frequency of Transponder to 2414 MHz. 18. Keep the Downlink Receiver to 2414 MHz. 19. Connect the Audio/Video signal at the input socket provided on the Uplink transmitter, Video at video input and audio at Audio I input. 20. Connect TV monitor to the Audio/Video output of Downlink receiver. (Video from Video output, audio from Audio I output) Set TV in AV Mode. 21. The TV monitor will display video and audio signal that you have connected to uplink Transmitter input. 22. Now change uplink-transmitting frequency from 2468 to 2450 MHz and correspondingly the receiver frequency of transponder is to be changed to 2450 MHz you will receive the same quality of signal at the output of the downlink receiver. 23. Now change the downlink frequency of transponder from 2414 to 2432 MHz and similarly change downlink receiver tuning frequency to 2432 MHz you will be receiving the same quality of signal. Try different combinations of uplink and downlink frequency and also by using tuner of receiver. 24. When the transmitter and receiver both are at same frequency you will see the distortion on monitor because both uplink and downlink frequency are same and receiver is receiving two links. 1. Direct 2. Through satellite. This will cause disturbance in the receiver. Result : The above shows a successful establishment of satellite audio/video link between Uplink transmitter and Downlink receiver at different up-linking and down-linking frequencies. 80 Experiment 7 Objective : Transmitting and receiving three separate signals (Audio, Video, Tone) simultaneously through satellite link Equipments Needed : 1. Uplink Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. 5. Satellite Transponder (Trans-receiver) 6. Function generator Procedure : 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter and frequency display will come on. 3. The transmitting frequency can be selected by Frequency Selection switch. The frequency can be changed from 2450-2468 MHz. 4. The transmitter „On-Off? toggle switch will switch „On-Off? the transmission. 5. Connect X1 Antenna to Uplink transmitter with BNC -BNC lead. 6. Set the OUTPUT gain of Uplink transmitter to maximum. 7. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10 m.). 8. Connect the Downlink Receiver to the AC Mains and switch it „On? by mains switch. 9. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. 10. The Downlink receiver „On-Off? toggle switch will switch „On-Off? the receiver. 11. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 12. Align both the Transmitter and Receiver Antenna's in line. 13. Place a Satellite Transponder between Transmitter and Receiver at a convenient distance; preferably all three can be placed in equidistant triangle of distance 5-7m. 14. Connect the Satellite Transponder to the AC Mains and switch it „On? by mains switch. 15. The Receiver side of Satellite Transponder has an „On-Off? toggle switch, which will switch „Off? the receiver of satellite. Similarly „On-Off? toggle Switch „On? Transmitter side will switch „Off? transmitter of satellite. 81 16. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency also to 2468 MHz. 17. Keep Downlink Frequency of Transponder to 2414 MHz. 18. Keep the Downlink Receiver to 2414 MHz. 19. Connect the Audio/Video signal at the input socket provided on the Uplink Transmitter, Video at video input and audio at Audio I input. And Connect Tone out signal to Audio II input of the Uplink transmitter by patch cord. 20. Connect TV monitor to the Audio/Video output of Downlink receiver. (Video from Video Output, audio from Audio I output) Set TV in AV Mode. Keep Downlink receiver voice switch in the „On? position. 21. The TV monitor will display video and audio signal that you have connected to Uplink Transmitter input. And you will be able to hear tone in the speaker of receiver. Result : Three separate signals (Audio, Video, Tone) are successfully received at downlink receiver through satellite communication link. 82 Experiment 8 Objective : Transmitting and receiving function generator waveforms through satellite link Equipments Needed : 1. Uplink Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. 5. Satellite Transponder (Trans-receiver) 6. Function generator Procedure : 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter and frequency display will come on. 3. The transmitting frequency can be selected by Frequency Selection switch. The frequency can be changed from 2450-2468 MHz. 4. The transmitter „On-Off? toggle switch will switch „On-Off? the transmission. 5. Connect X1 Antenna to Uplink transmitter with BNC-BNC lead. 6. Set the OUTPUT gain of Uplink transmitter to maximum. 7. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). 8. Connect the Downlink Receiver to the AC Mains and switch it „On? by mains switch. 9. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. 10. The Downlink receiver „On-Off? toggle switch will switch „On-Off? the receiver. 11. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 12. Align both the Transmitter and Receiver Antenna's in line. 13. Place a Satellite Transponder between Transmitter and Receiver at a convenient distance; preferably all three can be placed in equidistant triangle of distance 5-7m. 14. Connect the Satellite Transponder to the AC Mains and switch it „On? by mains switch. 15. The Receiver side of Satellite Transponder has an „On-Off? toggle switch, which will switch „Off? the receiver of satellite. Similarly „On-Off? toggle Switch „On? Transmitter side will switch „Off? transmitter of satellite. 83 16. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency also to 2468 MHz. 17. Keep Downlink Frequency of Transponder to 2414 MHz. 18. Keep the Downlink Receiver to 2414 MHz. 19. Connect function generator sine wave output to DATA input terminals provided on uplink transmitter. 20. Connect data outputs of downlink receiver to the Oscilloscope. 21. Feed the signal of 1 KHz Sine wave and you will observe similar sine wave of same frequency on Oscilloscope. 22. Change Sine to Square, Triangular, etc and you will observe the same wave shape on CRO. Result : Function generator waveforms are successfully received at downlink receiver through satellite communication link. 84 Experiment 9 Objective : Transmitting and receiving PC data through satellite link Equipments Needed : 1. Uplink Transmitter 2. Dish Antennas 3. Downlink Receiver 4. Connecting cables. 5. Satellite Transponder 6. RS232 cables -2 Nos. 7. 2 Male-to-1 Female RS232 cable 8. Preferably 2 sets of PC's (even one will do) 9. STPL Sat software Procedure : 1. Connect the Satellite Uplink transmitter to AC Mains. 2. Switch „On? the transmitter by Mains switch and frequency display will light up. The transmitting frequency can be selected by Frequency Selection switch. The frequency can be changed from 2450-2468 MHz. 3. The transmitter „On-Off? toggle switch will switch „On-Off? the transmission. 4. Connect X1 Antenna to Uplink transmitter with BNC -BNC lead. 5. Set the output gain of Uplink transmitter to maximum. 6. Place Downlink Receiver at a convenient distance of 5-7m. (It can go even up to 10m.). 7. Connect the Downlink Receiver to the AC Mains and switch it „On? by mains switch. 8. The Downlink Receiver Frequency can be changed from 2414-2432 MHz. 9. The Downlink receiver „On-Off? toggle switch will switch „On-Off? the receiver. 10. Attach R2 Antenna to the Downlink receiver with BNC - BNC lead. 11. Align both the Transmitter and Receiver Antenna's in line such that both are in parallel alignment. 12. Place a Satellite Transponder between Transmitter and Receiver at a convenient distance; preferably all three can be placed in equidistant triangle of distance 5-7 m. 13. Connect the Satellite Transponder to the AC Mains and switch it „On? by mains switch. 85 14. The Receiver side of Satellite Transponder has an „On-Off? toggle switch, which will switch „Off? the receiver of satellite. Similarly „On-Off? toggle Switch „On? Transmitter side will switch „Off? transmitter of satellite. 15. Adjust transmitter uplink frequency to 2468 MHz and transponder receiver frequency also to 2468 MHz. 16. Keep Downlink Frequency of Transponder to 2414 MHz. 17. Keep the Downlink Receiver to 2414 MHz. 18. Connect RS232 cable from Uplink transmitter to one set of PC. 19. Connect RS232 cable from downlink receiver to second set of PC. 20. Switch „On? the PC's and install STPL Sat software on both PC's and Select communication port COM1 on both PC's. 21. When the link is established, the typed matter on first setup PC will be transmitted to second setup PC via. Satellite link. (If transmitted data is not received correctly then adjust Gain potentiometer of Satellite transponder.) Note : 1. For successful Data Transmission, alignment of transmitting Antennas and Receiving Antennas should be parallel. 2. STPLSAT software is also used to establish a link by using single PC, by connecting Uplink transmitter, Downlink receiver and PC through a 2-Male to 1 Female RS232 cable. Result : PC data transmitted from first setup PC is received in the second setup PC via. Satellite link. 86 Warranty 1. We guarantee the product against all manufacturing defects for 24 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty. 2. The guarantee will become void, if a) The product is not operated as per the instruction given in the operating manual. b) The agreed payment terms and other conditions of sale are not followed. c) The customer resells the instrument to another party. d) Any attempt is made to service and modify the instrument. 3. The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc. 4. The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer. List of Accessories 1. BNC to BNC Small .................................................................................4 Nos. 2. Audio-Video Cable 2 Pin ........................................................................2 Nos. 3. BNC to Banana .......................................................................................2 Nos. 4. Patch Cord 8” ..........................................................................................2 Nos. 5. Microphone (Ahuja) ................................................................................1 No. 6. Mains Cord .............................................................................................3 Nos. 7. Pencil Cell (Microphone) ........................................................................1 No. 8. Dish Antenna ..........................................................................................4 Nos. 9. Plastic Box of Antenna ............................................................................1 No. 10. Cable RS232 ...........................................................................................2 Nos. 11. Cable RS232 (2m-1fm) ...........................................................................1 No. 12. CD-ROM ................................................................................................1 No. 13. CD-BOX .................................................................................................1 No. 14. Accessories Box ......................................................................................1 No. 15. Operating-Manual (PC Software inclusive) .............................................1 No. 16. Dust Cover ..............................................................................................1 No. Updated 18-07-2008 87