(The effective transmission of low-frequency signals needs to be modulated by high-frequency signals, and the high-frequency signals are used as carriers to transmit the signals, and different modulation methods can be used. In radio broadcasting, it can be divided into two modulation methods: AM and FM. Nowadays, FM or AM radios usually use superheterodyne, which has the advantages of high sensitivity, good selectivity and low distortion. In this course design, I chose superheterodyne income.)
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