You can search the tuning of the radio online and adjust it carefully.
I'll forward one to you. I hope it helps.
Unified adjustment of heterodyne radio
1. What is the unified tuning of heterodyne stations?
If a radio is assembled correctly and the working point is debugged correctly, it can generally receive a local radio station with strong transmission power after being connected to the power supply. But even so, it cannot be said that the effect is good. At this time, its sensitivity and selectivity are still relatively poor. It is necessary to precisely tune its various tuning loops at the specified frequency in order to give full play to the working efficiency of the circuit and make the performance indexes of the radio station meet the design requirements. The process of adjusting the tuning loop of superheterodyne radio to make it work harmoniously is called unified tuning.
Table 4-4-2: Resonance frequency of each tuning loop
A note on the resonant frequency of adjusting elements in tuning circuits.
Input circuit C 1a fine-tuning 535kHz double connection full precession.
1605kHz duplex is all screwed out.
Local oscillator circuit C 1b fine tuning 1000kHz double connection full precession.
2070kHz duplex full spin-out.
The core of the first intermediate amplifier T3 is 465kHz.
The core of the second intermediate amplifier T4 is 465kHz.
Suppose we want to receive a medium-wave and low-end radio station with a frequency of 535kHz. Of course, the input loop (magnetic antenna T 1 and capacitor C 1a) must be adjusted to 535kHz. Then, where should the resonant frequency of local oscillator circuits (T2 and C 1b) be adjusted? As mentioned above, according to the working principle of superheterodyne radio, the local oscillator frequency should always be higher than the resonant frequency of the input loop by an intermediate frequency (that is, 465kHz), that is, the local oscillator frequency at this time should be 1000kHz. When we want to receive a high-end radio station with 1605kHz, the frequencies of the input loop and the local oscillator loop should be adjusted to 1605kHz and 2070kHz respectively. In this way, every time we receive a radio station, we have to tune two places at the same time, that is, rotate two variable capacitors respectively, which is very troublesome. Actually, we dialed C 1a and C65438. In this way, C 1a and C 1b have a problem of keeping step with each other, that is, it is required to ensure that the resonance frequencies of the input circuit and the local oscillator circuit are different by an intermediate frequency at any angle, which is the purpose of unified debugging. In addition, the two midpoints should also be accurately adjusted to 465kHz. See Table 4-4-2 for the resonance points of each tuned circuit after unified adjustment.
Second, how to make a unified adjustment
High frequency signal generator is used for unified debugging. The high-frequency signal generator is like a small radio station, which can send out signals with different frequencies as the standard for correcting each tuning loop. S2 108 six-tube machine * * * has four tuning loops (t 1 ~ t4), which need to be carefully adjusted, and one by one should be adjusted to the predetermined resonance frequency. The adjustment method can be carried out according to the following steps:
1. Adjust the IF.
Turn on the power switch SA of the radio, turn the volume potentiometer RP3 to the maximum, and turn it into the double C 1 unit (turn it counterclockwise to the bottom). First, short-circuit the oscillation connection C 1b to stop the local oscillation, so as not to interfere with the intermediate frequency debugging. The signal generator outputs an amplitude modulation signal of 465kHz. One end of a 0.5-meter-long wire is connected to the high-frequency output end of the signal generator, and the other end is close to the magnetic antenna of the radio. High frequency signals are injected into the radio by electromagnetic induction. At this time, you should hear the low-frequency cry of 1kHz. Use a non-inductive screwdriver (a screwdriver made of nonmagnetic nonmetallic materials) to gently turn the magnetic caps of T4 and T3 in the middle of the week to make the speaker make the loudest sound. The adjustment sequence is from back to front, with T4 adjusted first and T3 adjusted later. If the sound in the speaker is too loud, you can turn down the potentiometer appropriately and then adjust it in the middle. Because people's ears are sensitive to the sound with low loudness, they can distinguish it with a slight change, but they feel slower to the sound with high loudness, so when debugging, just turn up the volume to just hear the sound of "blare …". Repeatedly adjust T4 and T3 for two or three times to maximize the sound in the speaker, and the intermediate frequency will be adjusted. After this debugging, don't forget to remove the short route on C 1b for the next debugging.
2. Adjust the coverage.
Coverage refers to the frequency range in which the radio can receive high-frequency signals. The coverage of medium-wave radio station is 535 khz ~ 1605 khz, and the corresponding local oscillation frequency range is 1.0 MHz ~ 2.07 MHz. The adjustment steps of coverage are as follows:
(1) Make the signal generator output an amplitude modulation signal of 520kHz, screw all the double C 1 in (counterclockwise to the end), adjust the magnetic cap of T2 with an induction screwdriver, and find the resonance point to make the sound emitted by the speaker maximum. At this time, it is the low end of adjusting frequency coverage, and the frequency value of 520kHz is left with a margin of 3%.
(2) Make the signal generator output 1650kHz, with a 3% margin. Turn all the double connections C 1 out (clockwise to the end), and adjust the fine adjustment of C 1b (Figure 4-3-5) to make the sound emitted by the speaker be the maximum, which is at the high end of the adjustment frequency coverage. Adjust the high-end and low-end repeatedly, so that the frequency range just covers the middle frequency band of 535 ~ 1605 kHz.
Adjust synchronization
(1) causes the signal generator to output an amplitude modulation signal of 570kHz, and the duplex is fully rotated in first and then slowly rotated out, so that the low-frequency sound of 1kHz can be heard in the speaker, and the position of the magnetic antenna coil is carefully moved to maximize the sound.
(2) Make the signal generator output the amplitude modulation signal of 1500kHz, and then turn it in slowly after the duplex is completely turned out, so that the speaker can emit the low-frequency sound of 1kHz, and adjust the fine-tuning of the duplex input connection (Figure 4-3-5) to maximize the sound. Repeat the synchronous adjustment of high-end and low-end to make both ends sensitive.
After the adjustment of the above steps, the sensitivity and selectivity of the radio can basically meet the specified technical requirements.
Third, no instrument debugging method
Under amateur conditions, not every amateur has such an instrument as a signal generator. At this time, the signal of the radio station can be directly used for debugging.
Connect the power supply, turn on the power switch SA, and set the potentiometer RP3 to the maximum. At this time, the noise of "sand, sand" can be heard in the loudspeaker. Turn the dial of the double connection and receive a radio station with moderate intensity first, so that you can hear the broadcast clearly. Adjust T4 and T3 in the middle of the week to maximize the broadcast sound of the radio station, and repeatedly adjust the intermediate frequency for 2~3 times. This intermediate frequency is not necessarily 465kHz, although it does not meet the technical standards formulated by the state, it will not have a significant impact on the performance of the radio station.
Turn the double capacitor and try to receive the lowest radio station in the medium wave. For example, fans in Wuhan can receive Wuhan Traffic Station (603kHz), and the frequency indication on the double dial may deviate from 603kHz. Turn the double capacitor again so that the dial pointer points to 603kHz. At this time, the Wuhan traffic station that has been received may have run away. Keep the position of the double capacitors fixed and adjust the magnetic cap of T2, so that the broadcast of Wuhan Traffic Station will appear again. This roughly adjusts the coverage of the low end. Let's find another high-end radio station, such as Chutian Economic Station (1 179kHz). Turn the double connecting rod so that the dial pointer reads 1 179kHz. Similarly, this station may not receive it at this time. Adjust the fine-tuning capacitor of the double-link oscillator C 1b (see Figure 4-3-5) to receive this station again, so the high-end coverage is also adjusted. Repeat this step for two or three times and you will be basically adjusted. Of course, the coverage accuracy of this phone is relatively poor, but as long as all local radio stations can receive it. If the local low-end radio station can't receive it, you can screw on T2' s magnetic cap. On the other hand, if the high-end radio station can't receive it, turn down the fine tuning of the oscillator and receive all local medium-wave radio stations.
Synchronization adjustment is also similar to the above. Firstly, rotate the duplex to receive a low-end radio station, toggle the magnetic antenna coil and change its position on the magnetic bar to make the radio station broadcast the loudest sound; Then switch to double connection to receive a high-end radio station, and adjust the fine-tuning of double input connection to make the radio station play the loudest sound. Repeat the above steps for two or three times, and the debugging of the radio will be completed. You don't need any instruments when debugging, as long as you operate carefully, you can achieve satisfactory results.
The superheterodyne six-tube machine circuit introduced in this chapter is the author's work of optimization and assembly for many times. As long as the parts are of good quality and carefully assembled and debugged, good results can be achieved. We have listened to the prototype, and we can receive Hong Kong and Taipei radio stations in the morning and night in Wuhan, and many provincial radio stations in the surrounding areas of Wuhan, such as Hunan, Jiangxi, Shandong and so on, on clear nights.
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