Introduction - If you have any usage issues, please Google them yourself
Extraction: (receiver)
IF signal 20M (sampling rate is 50M) down-conversion signal MIX_O 1M (50M) using CIC filter down sampling rate.
Interpolation: (sending side)
Baseband signal up to 1M, the sampling rate is 2.5M, using CIC filter for sampling rate processing.
Note: The up-sampling rate or down-sampling rate does not change the center frequency of the original signal, but the spectral distribution will change.