Author: Zhao Ping Liang Siwang
The six-range radio is a medium-band adjustment of a pocket semiconductor radio. The frequency coverage is 535 ~ 1605kHz, output power, no loss of 50 mW; maximum power is 150 mW.
I. Circuit composition and various circuit functions
The circuit composition of the radio is shown below. It mainly includes receiving circuit, high frequency amplification and frequency conversion circuit, medium frequency amplification, detection, audio amplification (including power amplification). Its various circuit functions are as follows.
1. The receiving loop is constructed by the magnetic rod coil L1 and the variable capacitor C1a. When the reception circuit is connected in series with the frequency signal of the air station, the current in the circuit is the largest, and the signal can be coupled to the variable frequency stage by L2, and the radio signal of the resonance is suppressed and the radio cannot be invoiced. Therefore, the receiving circuit is also referred to as a set set circuit. 2. The high-frequency amplification and the variable frequency circuit are coupled to the base of the VT1 by the radio signal selected by the reception circuit, and after amplifying the native oscillation signal input by the emitter, it is connected to the collector. The medium-cycle resonator B3 selects an intermediate frequency signal (Fbook -f and = f = 465 kHz), and feed it to the next level in the frequency amplifier. 3. Put the VT2 and VT3 in the two levels to the intermediate frequency signal to select and enlarge. 4. The detection circuit is completed by the nonlinearity and low pass filtering of VT3. The role is to detect the audio modulation signal (useful signal), remove the medium frequency carrier signal, and then send the audio signal to the volume potentiometer W via resistance R6. The base is sent to the base of the preamplifier VT4 via capacitor C8. Capacitors C5, C6 are the bypass capacitance of the intermediate frequency signal. 5. The audio preamplifier VT4 is an audio preamplifier. It functions is to enlarge the input audio signal to enter the push-pull power amplifier in two sets of signals opposite to the second transformer secondary. 6. The audio power amplifier constitutes a push-pull power amplifier by VT5 and VT6. Where the VT5 amplifies the positive half of the audio signal, the VT6 amplifies the negative half week of the audio signal, and uses the secondary of the output transformer to push the audio signal for half a week to push the speaker.
Second, the selection and detection of the circuit components This is an important part of ensuring that the whole machine is impaired. Because only the guarantees of the components are qualified products, they can install the quality radio. 1. Resistors and potentiometers This machine has an 8-color ring resistance and a potentiometer. (1) The resistance used by the color ring resistance this machine is a tetra-ring ring resistance. The last ring is gold or silver, is an error ring. The remaining three ring is the resistance ring, the number of the first color ring represents the first effective number of the resistance, the number of the second color ring represents the second effective number of the resistance, the third color ring representative The number is the multiplier of the resistance is 10n (n is a color representation of the color J. The fourth color ring represents the error of the component, the unit of the resistance is ohm. Its color standard symbol is shown in the table below.
Representative meaning
Silver gold black brown red orange yellow green blue purple gray white
Effective Number 0 1 2 3 4 5 6 7 8 9
Multiplier (quantity)
10 / -2 square)
10 / -01
10/0 times
10 / (1 party
10/2
10/3 times
10/4
10/5 times)
10/6
10/7
10/8 times
10/9 times
Value Value Allow Error (%)
± 10
± 5
± 20
Example: Ring is a red-yellow orange gold resistance value of 24x103 (± 5%), 24kΩ, error is ± 5%. Another example is a green brown silver flame value of 51 × 10 ° (± 10%) 51Ω, the error is ± 10%. The resistor reads the color ring and verifies with the electrical resistance of the multimeter, and it is sequentially marked on the white paper, which is convenient to take advantage of it in the loading. "*" Is a resistance symbol. (2) The potentiometer uses a potentiometer with a switch. There are 5 pins, wider two feets are switches, and the remaining smaller 3 feet are three pins of variable resistors, and the two sides are fixed ends of the resistor, the intermediate terminals are resistive active ends. When detecting, the multimeter is turned to the electric barrier, and the resistance of the multimeter × 100 block, a table pen is connected in the middle, and the other table is connected to the two fixed ends. When the rotation shaft, the resistance value should be continuously changed from 0 ~ 5kΩ. Or from 5 to 0kΩ, the intermediate table needle cannot be moved, and the potentiometer is intact.
2. Capacitors and double-linkable capacitors This machine has a non-polar capacitor 7 and one double-connected variable capacitor. For non-polar capacitors having less than 1μF capacitance, it is possible to use a multimeter electrical barrier 1K gear measurement, and the resistance value between the two pin should be infinite. Two-connected movable films are connected together, with a multimeter resistance 1K gear, a table brush, and the other, the other table is attached to the pin, the rotary shaft, the rotary shaft, and the pointer of the multimeter should stop in the resistance Infinity is the location, indicating that the variable power container has no tiny phenomenon, so that it can be applied. In addition, for a polar capacitor having a large capacity, a multimeter resistance 1K gear, a black table pen power capacitor positive electrode (long tube foot), red surface pen power capacity negative electrode (short tube foot), the table needle should have an angle to the right episode, Then to the left to the infinity position.
3. Antenna coil, horn coil, medium transformer and input / output transformer (1) Antenna coil antenna coil is a nylon tablet on a magnetic rod with a paint line to a nylon tablet on the upper surface, such as the top. The purpose of the pad nylon tablets is to move on the magnetic rod using the coil. The measurement is measured with a multimeter, and the pin 1, 2 should be a path, and 3, 4 should be a passage (the paint of the head of the lead should be scraped off the tin). (2) The local oscillation coil B2 is a horn coil, and its outer shape is the same as the neutralization. The number of pins is also identical. There is a passage between 1, 2, and 3 pins of the local oscillate, which is a coil with intermediate taps. The 4, 5 feet should be a passage, which is a coil. (3) The medium-cycle transformer B3, B4 is a medium-cycle transformer, and the 1, 2 feet is a coil, and 3, 4, 5 is a coil with a joint, which should be a path. The difference from the vibration coil is that the bottom is equipped with a capacitor, and the schematic shown in the figure below.
(4) Input Output Transformers B5, B6 are input, output transformers, their shape, size, and arrangement of the pin. Among them, 1, 2 foot is a coil, should be passage; 3, 4, 5 feet is a coil with a center tap, should be a path. The schematic shown is shown below. Input, the main difference of output transformers is that the resistance value of 1, 2 is different. The value of the input transformer is large, and the value of the output transformer is smaller (using R × 10 gear test).
4. Crystal triode, diode VTI, VT2, Vt3, VT4, and VT5 are NPN type crystal triodes. Their shape and pin are arranged exactly the same. The identification of the pin is: facing the model of the model, the pin on the left is the emitter E, the intermediate pin is the base B, and the right pin is the collector C. Method for detecting its magnification (1K gear) with a multimeter is: black table pen (battery positive electrode) connected in triode C. The red table pen (battery negative) is connected to E, which is that the clinic does not move, and then the resistance value of about 100kΩ is asked at the C pole and the base B, and the pointer swings one angle to the right, indicating that the triode has enlarged capabilities. Under the same conditions, the greater the angle of the pointer to the right, the stronger the enlargement. The VD is a crystal diode, and the resistance value is measured by ohmic 1K, and the resistance value in one direction is large (or small), the resistance value of the other direction is small (or large), and the resistance value is small, the black table pen is a diode Positive pole. One end of the crystal diode used in this machine is its negative electrode.
Be
Third, the equipment of the whole machine
1. The principle of the general installation principle is the first component (resistance, capacitance, voltage), first small, high, high, and gently. The spacing of the two pads is larger than the length of the component length, and is less than the length of the length of the component. 2. The processing of the printed board is generally long, and the pads will be oxidized, which is not easily welded, which requires the welding of the weld, which is loose. The production method of loosening water is: in the alcohol, it can be completely dissolved in alcohol. The printed board circuit is shown below.
3. The device of the component is in accordance with the principle of the installation, which does not need to be adjusted first. With horizontal resistors should be close to the printing plate, the resistor should be arranged in the middle of the two soldering holes; the direction of the color ring should be consistent. Using vertical resistors, the error is ringing down, and the other foot bends into an arc-shaped and the resistor parallel to the two pads, and then the no error is checked, and the excess port is removed. Secondly, insert the non-polar capacitor, the lower the better, then insert the electrolytic capacitor, pay attention to the polarity is not inserted (long feet is positive, the short foot is negative), must insert to the bottom, so as not to high, cover The lid is checked, and the excess pin is welded after the check is correct. Then insert the dual-chancapacitor (connected to the antenna nylon frame together with screws), volume potentiometers, local oscillators, two medium, input, input transformers, diode VDs, inspection, freely welding, and cut into excess points . After the above element is installed, check it out, be sure to guarantee that there is no misveired soldering, no lap. Finally, the triode is installed, pay attention to the three electrodes of the triode can't get wrong.
Fourth, debugging of the whole machine
1. Adjusting the static work point of the crystal triode (that is, the crystal triode in the circuits at each stage of the radio, should be in a certain static operating point. Whether the work point is appropriate to measure the current value indicated by the current table in the collector circuit. Draw the current table struck in the line (see the figure below), the current value of the set electrode is indicated by the table. Normally, LC, 0.4mA, IC2-0.9mA, LC3-1MA, IC4-1.5mA, LC5 & 6: One 2-5mA. Adjust. The direct current table is connected to the adjustment of the collector circuit and then adjust the bias resistance of the base. The method used is to connect its bias resistor position to a potentiometer (the resistance of the potentiometer is similar to the to-range resistance value, and is formed in series with a fixed resistor of half of the resistance value), the resistance of the potentiometer To the biggest. Then connect the DC power supply to see the indication value of the current table. If the current value is less than the normal value of the stage, the value of the potentiometer is reduced until the specified value is adjusted. If the power supply is connected, the indication value of the current table is greater than the normal value of the stage, and then the power-resistant potentiometer is debugged until the normal value is adjusted. Then, the potentiometer after normal value is removed, and the resistance is measured by the resistance, and finally, the fixed resistance is selected from the electrical resistance of the impedance value, and then look at the collector current, if the change is not changed. Big, it meets the requirements. When the static work point current is adjusted to the required value, the metal part of the small screwdriver hits the center end of the volume potentiometer, such as "咔" sound in the speaker, indicating that the low-input circuit of the radio has been Normal; if you can't hear "咔咔" sound, you need to further debug the low-discipline static work point until "咔咔" sounds. Then, the screw knife of the metal portion is taken to touch the VT3 base, and the speaker should be further increased than the original. The base of VT2 is touched by the same method, and the horn is more anticheed. The base of VT1 is reached with the same method, and the speaker should be maximized. This means that the DC operating state of the radio is basically normal. At this time, the rotating double-connected rotation axis can generally receive the radio audio signal.
2. Adjusting the Center Frequency Frequency (Mode Frequency) The purpose is to adjust the two medium-sized resonance frequencies to a fixed intermediate frequency frequency 465kHz. When adjusting the medium, it is necessary to use a non-sense screwdriver (a strait small screwdriver made of bamboo strips, used toothbrush, hard plastic sheet or rubber sheet). It is not advisable to use a metal screwdriver because the metal screwdriver is easy to cause the human body induction, and it is not accurate. The adjustment method is to open the radio casually listen to a radio station, and then use a wire or screwdriver to short the oscillation link (i.e., grounding the one end, and touch the other end to touch the oscillation). If the sound is immediately disappeared or significantly weakened, it will indicate that the change in frequency level and the local oscillation part of the circuit are working. If there is no effect on the sound, it means that the unit oscillation does not work, and the signal is passed through the middle level string. At this time, the adjustment week will become more and more messy. In this case, it should be found that the failure of the invincible, after excluding, the square can be adjusted. After the above-mentioned examination, it is determined that the frequency of the frequency is operated, and the large volume potentiometer can be opened, and the magnetic antenna sensing radio signal has directionality, and the magnetic antenna is rotated. Make the input external signals as small as possible, move the position of the antenna coil on the magnetic rod to make the sound as large as possible. Then use the homemade unusual screwdriver, slowly rotate the magnetic cap in the middle of the week, so that the sound reaches the most. The order of adjustment is from the back forward, that is, from B4 to B2, but when the sound is very sound, the change in the sound of the sound is often difficult to distinguish, so it is not easy to adjust more accurate, so the first adjustment will weaken out. The intensity of the signal is again adjusted; or the volume can also be reduced from the volume potentiometer, and then the above method is followed by two or three times. After the medium is adjusted, that is, the magnetic cap core screw each medium can be opened with wax.
3. Adjusting the frequency range (for the scale) The purpose is to include the entire band (535 to 1605 kHz) between the minimum frequencies of all the rotation from all of the rotation. This goal is to achieve by adjusting the magnetic core of the unit's oscillation coil and the compensation capacitor CB0 of the oscillation loop. When all of the doubles are screwed, the tick pointer refers to 53 (i.e., 530kHz), when both all rotate, the pointer finger at 160 (ie 1600 kHz). Then, listen to a radio station of the low end. For example, the Central People's Radio Station is 640kHz. Rotating double connection makes the pointer finger at 640 position (ie 640 kHz). If you can't receive this location, it can be rotated double even. If the pointer is less than 640, it means that the oscillation coil is insufficient, and the magnetic cap of the oscillation coil can be rejected into some until the 640kHz position. So far, if the pointer is received, the inductor of the oscillation coil is large, and the magnetic cap of the oscillation coil can be rotated out until it can be received at the 640 kHz position. Next, choose a high-end station, if the position is biased, the fine-tuning capacitor CB0 can be adjusted to receive this radio. It is worth noting that the fine-tuning capacitor C∞ changed the low end and disordered, so it also needs to return to the low end to adjust. In this way, the low-end oscillation coil magnetic cap, high-end adjustment capacitance ... to be repeated several times to finalize it. The easiest way is to use the adjusted radio to find high and low-end stations for adjustment. 4. Mode (i.e., the sensitivity of the adjustment machine) is to make the oscillation frequency of the unit can always be more than 465 kHz higher than the received signal. That is to say, their difference is fixed to the fixed intermediate frequency 465kHz, and the intermediate frequency can be smoothly passed through the intermediate frequency amplifier. So adjust the oscillation frequency of this unit is the main factor in improving the playback capabilities. However, it is more difficult to reach the local oscillation frequency. It is more difficult to have a fixed intermediate frequency of the received signal is 465kHz.At present, only the high-end, middle and low end three points of the unit oscillation frequency are higher than the receiving signal, 465kHz, which is usually said, "three-point regulation" or "three synchronization". The specific method is to use the low-end radio received when the frequency range is adjusted, the position of the magnetic antenna coil on the magnetic rod, so that the volume is maximized, so the low end is initially adjusted. then. Re-use the high-end radio at the adjustment frequency range to adjust the fine-tuning capacitor Ca0 in the input loop, so that the sound is the most, so the high-end is also initially adjusted. However, pay attention to it, like the frequency range, the high and low end must be repeated several times. When the high and low end is initially adjusted, the medium can be finely adjusted. To this end, a radio station can be listened to a radio station near 1000kHz, and the sound of the fine-tuning capacitor CA0 sound is relatively sound. At this time, there are three cases: First, when the capacitor CA0 is in the original, the sound is high, medium, and low three points have gain a tonal; Second, increasing the capacitance of CA0 can make the sound to the maximum, indicating that the capacitance CB1 in the oscillation circuit should be increased, (see the figure below) and re-regulate the capacitance to reduce CA0 to achieve the maximum If the capacitor CB1 should be reduced and the tone should be re-regulated. In short, CA0 is the largest in the fixed position, medium and low, and is the purpose of reaching the three-point regulation. After adjustment, the antenna coil is fixed with a wax. Finally, it needs to be explained. The radio does not have a capacitor CB1, which can only be tapered, low end adjustment.
5. The radio is always installed after the radio is complete, and the debugging work is completed. It can be installed. The method is to remove the speakers, the power cord, the printed plate element face is close to the chassis. The speaker is placed in the slot, and the connection of the battery clip is connected to it. "
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