(The effective transmission of the low-frequency signal needs to be modulated by the high-frequency signal, and the high-frequency signal is used as the carrier to transmit the signal, 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 generally use superheterodyne, which has the advantages of high sensitivity, stable operation, good selectivity and low distortion. In this course design, I chose superheterodyne income.)
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