Methods to improve transmitter sound quality and transmission distance

one:

1. Choose a good sound source. The sound source is a bottleneck. You can choose according to your needs. If you want to make a radio station, please choose broadcast-level CDs and LDs. Generally, computers, MP3, CDs, MDs, VCDs, microphones, and other portable players can be used as sound sources.

2. The sound source transmitted to the transmitter must use the shortest shielded wire possible. Note that there should be no AC signal difference between the transmitter and the sound source. In fact, when both the sound source and the transmitter use AC power, it is easy to introduce AC noise and deteriorate the sound quality. The solution is to use battery power for one or both, or put both into a shielded box or even share a power line.

3. Some low-end audio sources have a lot of noise. The ground wire of the audio line must be connected correctly, otherwise, the noise will be very loud (many digital decoders are dedicated to the ground of audio analog signals. If it is connected to the wrong place, although it is the same wire with zero resistance, the noise is really unforgettable.). At this time, everyone should use shielded wires to lead out the audio signal as close to the digital decoding chip as possible. (In this case, it is best to separate the power supply, which can save a lot of trouble.)

4. The audio signal is not a single signal, but a signal of a frequency band. Therefore, it is recommended that friends who have the conditions should add a passive tone control part in front of the wireless transmitter, so that the final auditory effect can be properly adjusted. This can improve the sound quality to a certain extent (actually improve the hearing sense).

5. Now we come to the modulation part. I think it doesn't matter what type of oscillator is used. The most important thing is stable frequency, good waveform, stable amplitude, and easy modulation.
Oscillators made directly from crystal oscillators are not conducive to frequency modulation. Even if the frequency is multiplied multiple times, the modulation index may be difficult to reach the required level. It is not recommended.
As for modulation, the waveform of the oscillator is mainly affected by the Q value of the LC circuit. The higher the Q value, the smaller the frequency distortion. If conditions permit, you can add a variable capacitance tube to the LC circuit to modulate the frequency. In this way, you can obtain any modulation index and good linearity, which is conducive to improving the sound quality (it is better to use a variable capacitance tube with three pins for symmetrical compensation. I still have a few old ones that I disassembled.). In general, changing the PN junction voltage of the triode can also achieve a better modulation effect. The wireless transmitter of this website, which costs a few yuan, is like this. The effect is still very good, and the sound quality can't be heard at all.

6. Modulation must be transmitted. If the modulator is used for transmission, it will be a bit troublesome. The antenna is both a load and a part of the oscillation circuit. On the one hand, the antenna affects the Q quality of the circuit, and on the other hand, it affects the stability of the transmission frequency.

However, it is so simple that it works just fine once installed, is easy to debug, and works well. As long as you don't touch it, it works well.

7. Increase the transmission amplifier stage. Transmission amplifier has three functions: first, it can reduce the influence on oscillation and make the frequency more stable; second, it can further select frequency filtering, requiring only useful frequencies to be transmitted and transmitting waveforms without distortion, which can avoid interference with other frequencies and improve transmission efficiency; third, it can increase the output power, which is the best way to increase the transmission distance.

8. The more stages a transmitter has, the more complex the circuit is, the higher the Q value of the LC loop is, the more complex it is to debug, and the better the effect after debugging (reflected in long distance and less interference with other frequencies). If you install a multi-stage transmitter and can receive on several frequencies on the radio, this means that it is not installed well and is not adjusted well (it should only be received on one frequency).

9. When adjusted to the best state, there is only one place where the signal can be received, and the distance can be reached as far as possible.

10. Because it is difficult to adjust to the best state in amateur situations, and in order to take care of multiple transmission frequency points, the general output stage mainly plays an amplification role, and the frequency selection role is not very large. Otherwise, you must re-adjust after each frequency change. If you can adjust this site's 9 yuan wireless microphone to the best state, your level is very good.

11. The most difficult part of wireless transmission is the inductor. To increase the Q value of the coil, it is recommended to use thicker copper wire, preferably silver-plated (gold-plated is better) coils. I personally think that the Q value of the inductor with a high-frequency magnetic core will be higher, while the Q value of the inductor with a copper core will be lower (because copper is a conductor, it has loss, and it may also reflect and absorb high-frequency signals, and even distributed capacitance may have an impact.)

two:

1. If you want to increase the transmission power, please increase the power supply voltage and operating current. As long as it does not exceed the maximum voltage and power of 9018, the transmission distance should be able to be increased.

2. Theoretically, if you only transmit 1mW radio waves, you can receive them at 10 kilometers or even farther away. You just need to find a way to improve the sensitivity and selectivity of your radio. You can imagine how strong the radio waves from Mars are when the United States receives them.

It is easy to make a KW-level wireless transmitter on Earth. If a Martian robot has to work with a KW-level transmitter, it will definitely need to rest for a day to recharge after speaking a word.

3. Although the magnetic core inductor has a high Q, it is difficult to adjust and may be broken if not adjusted properly, while the copper core inductor cannot be broken.

4. In cities, there are too many radio stations. It is almost difficult for a highly sensitive radio to receive blank frequencies. This also brings uncertainty to the test of wireless transmitters, because the radio can easily be "grabbed" by strong radio stations, thus shortening the receiving distance.

5. In the city, there are many interference sources, and it is impossible to test the maximum distance of transmission and reception. Maybe the radio has a "masking effect" just like people hear sounds. For this, we can only increase the transmission power to increase the distance.