The function of high-frequency electronic circuit is to process high-frequency signals, including oscillation, amplification, shaping, mixing, frequency difference, frequency selection, carrier, modulation, demodulation and logical operation. Its main feature is that it can work at high frequency.

It uses the reflection of the ionosphere, so the communication distance can reach thousands of kilometers, and it is used to keep in touch with the base and distant air stations during flight. The frequency range used is 2 ~ 30MHZ, and every 1KHZ is a channel. Large aircraft are generally equipped with two sets of high-frequency communication systems, using single sideband communication, which can greatly compress the occupied frequency band and save transmission power.

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The specific frequency distributions are:118.000 ~121.400 MHz,123.675 ~128.800 MHz and132.000 MHz.

121.100 MHz ~121.200mhz is used for air flight information service; 12 1.500MHZ has been designated as the unified channel for global distress calls. 121.600 ~121.925mhz is mainly used for ground control; It is worth noting that the communication signal is amplitude modulated, and both parties use the same frequency. When one side finishes transmitting, it stops transmitting and waits for the other side's signal.

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