常识--收音机原理 与故障检测（Common sense - radio principles and fault detection）

常识--收音机原理 与故障检测（Common sense - radio principles and fault detection） 常识--收音机原理 与故障检测(Common sense - radio principles and fault detection) Common sense: the radio principle and fault detection. If TXT is 10 million, I will buy 30 apartments to rent to others and collect the rent every day. It is not the prince or tang's monk who fully rides the white horse. The winged ones are not necessarily angels, sometimes they are birds. This article is contributed by okele168 The principle and failure analysis of the radio wave in 2009-12-18 09:07 and the transmitting and receiving of radio waves One, radio waves 1. The electromagnetic oscillations of radio waves in the surrounding space generate the electric fields and magnetic fields that change periodically, and spread out in all directions, forming electromagnetic waves. Electromagnetic waves used in radio, television and radio communications are called radio waves. Radio waves travel at about 3,000 km/s in space. The relationship between radio waves in an oscillating period T is called the wavelength, the relationship between the wavelength, the frequency and the propagation speed of the radio waves can be expressed in the following formula: In the formula, the wavelength, the unit is m; -- propagation velocity, unit m/s; F -- the frequency, the unit is Hz. From the above, the lower the frequency, the longer the wavelength; The higher the frequency, the shorter the wavelength. 2. The transmission mode of radio waves is mainly in the following three ways: (1) ground wave; (2) sky wave; (3) space wave; Modulation and demodulation 1. Modulation is the process of loading low-frequency electrical signals into high-frequency carriers. There are two types of modulation commonly used in radio broadcasts: (1) the modulation method that changes the amplitude of the carrier with the modulation signal voltage is called the amplitude modulation. (2) the modulation method that changes the frequency of the carrier with the modulation signal voltage is called FM. The spectrum of FM wave is more complex, and its frequency band width can be expressed as below: B = 2 (+ Fmax). B - band width; Maximum frequency deviation; Fmax - maximum modulation signal frequency. The process of removing the original modulation signal from a modulated signal at the receiving end is called demodulation. 1 -- main performance indicators of the radio A frequency range refers to the frequency range of the signal the radio can receive. Sensitivity when the output power of the radio reaches the rated power, the strength of the minimum signal required on the input side is called sensitivity, and the unit is (microvolt). It is used to indicate the ability of a radio to receive weak signals. Obviously the smaller the input signal, the higher the sensitivity of the radio. Three, selective selective said radio from including choose the useful signals in each frequency of complex signal and the ability to inhibit other interfering signal, selective to the input signal mismatch plus or minus 9 KHZ down to indicate the degree of sensitivity, units for the dB (dB). The greater the number of dB, the more selective the radio. 4. Output power output power refers to the power of the audio signal transmitted to the loudspeaker by the radio, and the unit is W (watt), also available in mW, 1W = 1000mW. The louder the output, the louder the radio can make. The circuit composition and signal flow of the 1-3 FM radio At present, radio receivers, whether or not, use superheterodyne receivers. So-called superheterodyne, is the high frequency signal receiving down, put it into a fixed frequency of intermediate frequency signal, and then amplification, demodulation receiving mode, it has received high sensitivity, good selectivity, stable work, etc, so widely used. The principle and failure analysis of 1-4 amplitude-modulation radio circuit 1. Input circuit 1, the action of input circuit From the antenna to the radio between the first stage amplifier circuit known as the input circuit, its role in a variety of signal from the antenna sensed the need of a selected signals, and transmitted to the next level circuit, while the other unwanted signal is effectively restrained. 2. The composition of the input circuit and the input circuit of the working principle radio are composed of the tuning coil L1 and the variable capacitor C, which USES the series resonance principle to select the desired signal. The process of regulating variable capacitance C, which resonates with the signals it receives, is called "tuning", which is usually the chosen platform. 3. The input circuit of the type of input circuit is mainly used in the input circuit of the magnetic antenna and the input circuit of the external antenna. 4. Fault analysis of input circuit (1) don't get When the input circuit of capacitance in short circuit, the high frequency of input signal is short circuit, radio receive a less than programs, but have "rustling noise, when the check can measure capacitance engagements pole piece, the resistance value between normal should be infinite. (2) the crosstalk crosstalk is listening to a radio station, the voice of the other units also mixed with time, the reason was that the input circuit coil wire break or more strands of wire broken stocks, lose input circuit tuning effect or selectivity is very poor. (3) low sensitivity causes low sensitivity due to input circuit capacitance leakage, coil breakage or dampness, so that the Q value of the input loop decreases. Two, the frequency conversion circuit 1, the action of frequency conversion circuit Frequency conversion circuit is super type is an important part of the radio, its role is to put the input circuit and high frequency modulation signal transformation for the intermediate frequency modulation signal of fixed frequency. 2. In tuning the radio, the vibration frequency is always 465kHz higher than the input loop in the whole frequency range, which is called the "general adjustment". 3. Failure analysis of frequency converter circuit (1) don't get If the vibration cannot produce the vibration signals of vibration, high frequency signal can't mixing to produce 465 KHZ intermediate frequency signal, V1 can only output high frequency signals, selected by intermediate frequency and high frequency signal frequency loop filter, lead to not receive radio show. (2) the failure of the sensitivity low pad capacitance, the oscillation of the oscillating coil and the loss of Q value, the bad adjustment of the system or the dissonance of the intermediate frequency selective frequency circuit will lead to the decrease of the sensitivity. (3) the large or poor performance of the large frequency converter tube or the failure of the capacitance of the emitter capacitor in the frequency converter can cause a large noise failure. Chapter ii principle and failure analysis of FM radio 2-1 circuit composition and signal flow of FM radio The main characteristics of FM broadcasting 1. Strong anti-interference ability and high SNR; 2. Good frequency band and sound quality; There are many channels available. Two, superheterodyne FM radio sets the block diagram and the signal process as shown in figure 2-1. In the antenna to the various frequency of high frequency signals, by selecting the required input circuit receives the (A), A high frequency FM signal after high amplification circuit, the inverter frequency, into A carrier frequency to 10. Intermediate frequency modulation signal of 7MHz (B). The intermediate frequency modulation signal is amplified to a certain amplitude by the middle frequency modulation signal, and then the amplitude modulator is used to suppress the parasitic interference and then send to the discriminator to demodulate. The frequency range of FM signal is reduced to a frequency range of 30Hz -- 15kHz audio signal (C), which is amplified by audio and reduced to sound by speaker. 2-2. Circuit principle and failure analysis of FM radio Frequency modulation hf head circuit The composition and function of frequency modulation high-frequency head circuit consists mainly of input circuit, high frequency amplifier circuit and frequency converter circuit. The function of FM high-frequency head is to select the FM radio signal to be received, and enlarge and mix it to a carrier frequency of 10. A medium-frequency signal of 7MHz and then transmitted to a medium frequency amplifier. The effect of FM radio 2, input circuit input circuit of the high frequency signal from the antenna to the FM band signal, it can be divided into fixed tuning type input circuit and variable tuning, two kinds of circuit type input circuit. 3. The main function of high frequency amplification circuit is to enlarge the frequency modulation signal to improve the receiving sensitivity of FM radio. High frequency amplifier circuit generally adopts the common-base amplifier circuit, this is because the base circuit of cutoff frequency is high, suitable for high frequency amplifier, and the base circuit of input impedance is low, easy to match the impedance of the antenna. The function of inverter circuit converter circuit is to convert the frequency modulation signal to a medium frequency signal which is fixed to 10.7 MHz. 5, AFC circuit of AFC circuit is special modulation radio circuit, it is used when the frequency of vibration in the working process of the drift occurs, can automatically control the local frequency back on the right frequency of FuJia FM radio in most states. Intermediate frequency amplifier circuit FM radio into the circuit and amplitude modulation radio: the main difference between a tuned circuit resonance frequency, the second is putting without automatic gain control circuit, frequency modulation to keep putting circuit gain, so as to limit. Iii. Limiter 1. The role of limiters is to inhibit this parasitic interference. 2. In the circuit of discrete components of the commonly used limiters, the diode limiter circuit or the transistor limiter circuit are generally used in the circuit, and the differential circuit is generally used within the integrated circuit. quadrupler 1, the role of the discriminator discriminator is the function of the FM signal demodulation, restore the original modulation signal, for example, in the case of FM radio, from a 10.7 MHz in intermediate frequency signal demodulation for audio signal. 2. The frequency discriminator process is divided into two steps. Make continuous FM signal by the linear transformation circuit into amplitude changes along with the frequency variation of frequency modulation signal frequency modulation amplitude modulation signal, then the frequency modulation signal amplitude change is required of audio signal demodulation, and then use detector out of the audio signal demodulation of FM modulation wave. 2-3 FM stereo broadcasting and receiving principle The concept of stereo Sound is produced by the vibration of an object, the vibrating object that produces a sound is called a sound source, and the sound travels through the medium to our ears so that we can hear it. In daily life, all kinds of sound source in the form of three-dimensional distribution around the perimeter of the us, they all have different sound to the listener's sense of direction, so we hear daily is stereo. FM stereo broadcast and reception FM stereo radio is compatible with monophonic broadcasting. The so-called compatibility refers to that the single channel receiver can receive FM stereo broadcast signal, when the sound of the loudspeaker is superimposed on the sound of the left and right sound of the stereo broadcast. Answer the question (1) 1. What is radio waves? What does the wavelength of radio waves have to do with frequency? If the wavelength of the wave is 300m, what is the frequency? If the frequency of radio waves is 600kHz, what is the wavelength of the radio wave? Solution: electromagnetic oscillations in the surrounding space produce the periodic change of electric and magnetic fields, and spread out in all directions, forming electromagnetic waves. Electromagnetic waves used in radio, television and radio communications are called radio waves. The relationship between the wavelength and frequency of radio waves is: the lower the frequency, the longer the wavelength; The higher the frequency, the shorter the wavelength. F = = 300000000 m/s, 300 m = 1000000 (Hz) Similarly: 12 to 600000Hz = 500 (Hz) 2. What are the modes of transmission of radio waves? What are the characteristics of their transmission? Which bands of radio waves are used for transmission? Solution: there are three main types of radio waves in space: (1) the characteristics of ground wave propagation are: propagation along the earth's surface. Suitable for medium wave and long wave. (2) the characteristics of sky wave propagation are: the reflection and refraction of the ionosphere are transmitted. Suitable for medium wave and short wave. (3) space wave propagation is characterized by the propagation of space along a straight line. Suitable for ultra-short wave and microwave adoption. What is modulation? Why do we use modulation in radio and communications? Solution: the so-called modulation is the process of loading low-frequency electrical signals into high-frequency carriers. Modulation is used in radio and communications to improve the efficiency of emission and prevent interference between signals. 4. What is the carrier, modulated signal and modulated signal? What methods are used by radio stations to achieve mutual non-interference? Solution: the carrier is a high frequency oscillation signal; The low-frequency signal is called the modulation signal; The high-frequency signal modulated by the main body is called a modulated signal. Radio stations use different frequencies to achieve the goal of non-interference. What is the amplitude modulation? What is FM? What is the width of their band? Solution: the modulation method that changes the amplitude of the carrier to the modulation signal voltage is called amplitude modulation; The frequency band width of the amplitude modulation wave is 2F. 6. What is demodulation? What is detection? What is a discriminator? Solution: the process of removing the original signal from the modulated signal is called demodulation; Different modulation methods have different demodulation methods. The demodulation of the modulated wave is called detection, and the demodulation of FM wave is called discriminating frequency. 7, What is the range of the medium and short wave frequencies of the FM radio in China? What's the middle frequency? Solution: the frequency range of the medium wave band of the FM receiver is 526.5 -- 1606.5 kHz, and the frequency range of the short-wave band is 2.3 -- 26.1 MHz. The frequency range is 87 -- 108MHz. What are the main performance indicators of radio? What are their meanings? The main performance indicators of the radio are: (1) the range of frequencies that a radio can receive. (2) sensitivity refers to the intensity of the minimum signal required on the input when the output power of the radio reaches the rated power. (3) selectivity refers to the ability of a radio to select useful signals from complex signals including various frequencies to suppress other interference signals. (4) output power refers to the power of the audio signal transmitted to the speaker by the radio. 10. The sensitivity of the radio is 2mV/m, and the selectivity is 20dB. The sensitivity of b radio is 5mV/m, and the selectivity is 10dB. Which of the two radios is sensitive? Which is selectivity? What is a superheterodyne receiver? How does it compare with the direct amplification receiver? Solution: the so-called superheterodyne, is the high frequency signal receiving down, put it into a fixed frequency of intermediate frequency signal, and then amplification, demodulation receiving mode, it has received high sensitivity, good selectivity, stable work, etc. 12, What is the function of the input circuit of the radio? Solution: from the antenna to the radio between the first stage amplifier circuit known as the input circuit, its role in a variety of signal from the antenna sensed the need of a selected signals, and transmitted to the next level circuit, signal and the other don't need to restrain effectively. 14. What are the functions and characteristics of magnetic rods in magnetic antennas? Characteristics of magnetic rod: 1. High permeability; 2. Directionality. The function of the magnetic rod: 1. Increase the receiver sensitivity of the radio. The maximum voltage can be induced. 15. What failures may occur when the input circuit fails? Solution: (1) not receiving the platform; (2) the stage; (3) low sensitivity. What is the function of the frequency conversion circuit? What three parts does it consist of? Solution: the frequency converter circuit is an important part of the ultra - external radio, and its function is to convert the high-frequency modulation signal transmitted by the input circuit to the frequency modulation signal of the fixed frequency. The variable frequency circuit consists of a local oscillator, a nonlinear device and a medium frequency oscillator circuit. 17. What is the frequency of the radio signal when the radio signals at a radio frequency of 1080kHz? What should the resonance frequency of its input loop be? What is the radio set? What are the methods for implementing the system? Solution: when the radio is tuned, the vibration frequency is always 465kHz higher than the input loop in the whole frequency range, which is called the "general adjustment". In general, there are two ways to achieve a general adjustment: one is the input circuit and the variable capacitance of the vibration loop with the same axial differential capacitance. Another method is to adopt the equal capacitance of the two capacitors, and the method of series capacitance is adopted in the tuning loop to realize the harmonization. What is the three-point rule? Briefly describe the effect of pad capacitance and compensation capacitance in this vibration loop. Solution: adopt the capacitance of constant volume, and adopt the method of series capacitance in the tuning loop to realize the harmonization; It is known as the "three-point rule" that the radio can realize the system at the low end, high end and middle of the receiving band, but at other receiving frequency points. When the cushion capacitance is greater than the compensation capacitance, the result is that the total capacitance of the loop decreases and the frequency of the vibration increases. On the contrary, the total capacitance of the loop increases and the frequency of the vibration decreases. 20. What failures may occur when the frequency conversion circuit fails? Solution: (1) not receiving the platform; (2) low sensitivity; (3) loud noise. 21. If this vibration stops, what is the failure phenomenon? What methods are used to check the vibration of the vibration during maintenance? Solution: if this vibration stops, it will not be able to receive the platform. During the maintenance, the high current of the transmitting pole of the frequency converter is large, and the high voltage of the emitter is checked. What are the functions of the intermediate circuit? What aspects of the system play an important role in the system? Solution: the function of the middle discharge circuit: 1. Improve reception sensitivity; 2. Improve selectivity. The intermediate circuit has an important influence on the selectivity, sensitivity and sound quality of the whole machine. 23. What are the possible reasons for the decrease in sensitivity of the radio in the circuit? Solution: it may be that the performance of the tube is decreased or the static working point is not normal, the capacitance of the emitter is failed, and the middle frequency resonant circuit is unharmonious. Second, refer to the answer What are the characteristics of FM broadcasting? Solution; The main features of FM broadcasting are: (1), strong anti-interference ability and high SNR; (2) frequency band width and sound quality; (3) there are more channels available. What is the frequency range of FM radio? What is its intermediate frequency? 3, a little 4. What is the role of FM high-frequency head? What parts of the circuit does it consist of? Solution: the function of FM high-frequency head is to select the FM radio signal to receive, and amplify and mix it to a medium frequency signal of 10.7 MHz, and then to the intermediate frequency amplifier. It mainly includes input circuit, high frequency amplifier circuit and frequency converter circuit. What is the difference between a fixed tuning and a variable tuned input loop? What are the pros and cons? Solution: (1) fixed tuning type the resonance frequency of the input circuit design on a fixed value, near 98 hz with fixed input circuit of high frequency FM tuner type head, only need to use double variable capacitor, a coupon for high output resonant circuit, the other for the vibration resonance loop. (2) variable capacitance is adjusted in the variable tuning input loop to make the input loop resonant with the frequency of the receiving station. The advantage of this is that it enhances selectivity, but it is necessary to adopt a triplet or multi-link variable capacitance. What kind of amplification circuit is used in hf amplifier in hf head circuit? What are the characteristics of this circuit? Solution: high frequency amplifier circuit is generally used in common base amplifier circuit. The cutoff frequency of the common base amplification circuit is high, which is suitable for high frequency amplification, and the input impedance of the common base circuit is low, and it is easy to match the impedance of the antenna. What is the difference between the frequency conversion circuit and the FM radio in FM radio? Solution: the frequency modulation radio adopts the high frequency capacitance three - point oscillator to make the vibration circuit, and the frequency of this vibration is controlled by the AFC circuit, and the automatic adjustment of the vibration frequency is realized. What is the function of the AFC circuit? And briefly describe how it works. Solution: the function of AFC is that when the vibration frequency is drifting in the working process, the frequency of this vibration can be automatically controlled to the correct frequency, so that the FM radio is in the optimal state of tuning. Its working principle is: when the frequency of the vibration is accurate, the carrier frequency of the frequency signal generated by mixing frequency is 10.17 MHz, and the dc component in the output voltage of the frequency discriminator is 0 or a fixed dc voltage. What is the difference between a medium and a modulation radio in a FM radio? The main difference is: firstly, the resonant frequency of the tuning circuit is different. The ground is the control of the circuit in the frequency modulation without automatic gain control, so that the middle and the circuit can be kept in a larger gain so as to realize the limit. 10. What does the limiter do? What kinds of limiters are commonly used? Briefly describe their limiting principle. Solution: the function of the limiter is to suppress the interference of parasitic amplifiers. Commonly used limiters: generally used in discrete component circuits, a diode limiter circuit or a transistor limiter circuit. Generally, the differential circuit is used in the integrated circuit. Diode limiter principle is: by diode V2, V3 and connect in parallel resonant L1C1 road ends, when the voltage is larger on both ends of the loop, V2, V3 conduction alternately, make the circuit voltage at the ends of the restrictions on the turn-on voltage of diode. The triode limit principle is: when the base of the triode enters the larger signal, the triode will enter the saturated zone and the cutoff region, so that the output signal is clipped to realize the limit. Differential limiting device limiting principle is: the differential amplifier tube V1 and V2 emitter by constant current source, make two triode emitter current is equal to the sum of fixed value I, when the input signal is larger, the saturated, V1 V2 cut-off during the positive half cycle, V1 cut-off, V2 saturation during the negative half cycle, the output of such as radial rectangular wave, so as to realize the limiter. What is the role of a discriminator? What are the two steps of the frequency discriminator? Solution: the role of the discriminator is to demodulate the FM signal. Reduction produces the original modulated signal. Frequency demodulation process is divided into two steps, the first continuous FM signal by the linear transformation circuit into amplitude changes along with the frequency variation of frequency modulation signal frequency modulation amplitude modulation signal, and then use detector from FM modulated wave in the audio signal demodulation in the industry. 12. 13. 14. What is the shape of the frequency discriminator? What are the main requirements for the discriminator? Solution: roughly the S curve, 15. When the resonant circuit in the discriminator is distuned, what failure will occur after the center frequency deviation? Solution: it can cause a decrease in volume, poor quality of sound quality, or silent failure. Why are FM radios set to accentuate circuits? Solution: by "preemphasis" solved due to the high frequency modulation signal after the problem of poor anti-jamming performance, hitches in makeup receiver when we get the original modulation signal frequency in turn to the high frequency component of the modulation signal attenuation, to restore to its original state, must carry out "to increase". What is stereo? How do people judge the orientation of different sound sources? Solution: sound is produced by vibrating objects, object known as the sound source, produce the vibration of the voice of the sound source in the form of three-dimensional distribution around the perimeter of the us, they all have different sound to the listener's sense of direction, so we hear daily is stereo. People's judgment of sound source location, rely mainly on "binaural effect", namely the human brain through to reach the ears of the time difference, phase difference, and poor strength and the synthetical analysis of the difference between these is quite small, so as to determine the location of each sound source. What do we mean by "stereo" in the sound range? Why do you have to use two sets of playback systems to make stereo sound? Solution: stereo is the sound recording and playback technique in stereo, which is based on the mechanism of sound localization. According to the "binaural effect", the two microphones are left and right in the sound field, and the sound is picked up as the left and right sound signal. In the play, as long as the left and right channel signal through the left and right of the two speakers placed, make the listener from left and right two sounds of each sound source differences and feel the different location of sound source, resulting in a three-dimensional effect. 19. What is the "compatibility" between FM stereo radio and monophonic FM broadcasting? Solution: the so-called compatibility refers to that the single channel receiver can receive FM stereo broadcast signal, when the sound of the loudspeaker is superimposed on the sound of the left and right sound of the stereo broadcast. In turn, a stereo receiver can also receive a single channel FM radio signal, but only two speakers make the same sound. 20. Draw the block diagram of the stereo signal encoding and emission system of the pilot frequency system, and briefly describe the coding process of the stereo composite signal. Review questions (3) reference answers 1. What steps do you usually go through to overhaul the radio? Solution: (1) to understand the situation to the user and make a trial listening to determine the fault phenomenon. (2) to analyze the working principle of the electromechanical circuit, The scope of the initial error. (3) use proper method to check and find the parts of the fault until the components. (4) repair, including adjustment and replacement of components. (5) if necessary, debug the repaired fault machine until it has a satisfactory listening effect. What are the methods used for repairing radio? Solution: (1) intuitive examination method; (2) voltage and current measurement method; (3) resistance measurement; (4) signal injection method; (5) signal tracing method; (6) substitution method; (7) ac short circuit method. 3. The signal injection method can be used to overhaul the faulty radio. Solution: the signal injection method is used to detect the sound condition of the speaker to determine the location of the fault after the proper test signal is injected from the rear to the fault machine. Applicable to inspect dc voltage, normal current of current and quiet or low sound. 4, what is the most common way to repair a radio? You can check out the problems in this way. Solution: the most common method is voltage and current measurement. This method is used to check the voltage, current value of the radio circuit in the multimeter and compare with the normal value to find fault. If the current of the whole machine is measured, if the current is too large, there is a short circuit fault. 5. Find out the reason why the current of a primary circuit is zero during maintenance. 6. The failure of a radio is completely silent, and the reasons for the failure are analyzed. Solution: (1) there may be broken lines; (2) the power supply voltage and the whole machine current are not normal: if there is no power voltage, low voltage, large current, small current, etc. (3) abnormal speaker; (4) the low discharge circuit is not normal. 7. The failure of a radio is not receiving the station, but there is obvious noise, and try to judge the scope of the fault. Solution: (1) the dc voltage and current are not normal at all levels; (2) the partial circuit of the detector is not normal; (3) part of the circuit is abnormal; (4) the frequency conversion circuit and input circuit are not normal. What are the characteristics of low sensitivity to the radio? Try to analyze the causes of low sensitivity. Solution: the characteristic is that the number of stations received is significantly reduced, and the main signal received is the local strong signal, but the volume is normal. The reason is: (1) the dc voltage current is abnormal; (2) circuit capacitance, resonance capacitance, coupling capacitance and other failures; (3) the radio failed to meet the technical requirements. What's the reason for the low volume of the radio? What method can be used for maintenance? Solution: the reason for the low volume is low low gain or poor speaker. During maintenance, the signal injection method can be used to find fault location, and the fault components can be detected by voltage current method or substitution method. 10. What is the adjustment of the frequency of the FM radio? How does the adjustment of the medium frequency affect the performance of the radio? Solution: the adjustment of the middle frequency is to adjust the magnetic core or magnetic cap of the intermediate frequency transformer. The adjustment of the medium frequency has a decisive influence on the sensitivity of the radio. 11. A radio station that receives less than the frequency range, The test analysis is due to which loop has not been adjusted and how to adjust. A radio that receives a range of radio frequencies is normal, but the receiving end of the radio is significantly reduced, and the sound is light, and the reason for the analysis is what should be adjusted. one