In GNURADIO when
RTL-SDR Source block is placed there is a parameter
Sample Rate (sps) and
I can put there for example 32kHz into
Sample rate and 107.5MHz into
Channel frequency to tune some FM station in my location. FFT block shows a signal of that station in a correct frequency as shown on the picture:
But according to Nyquist–Shannon sampling theorem,
Sample rate should be at least 2 times higher than signal frequency, so in this situation I should set at least 215MHz into
Sample rate parameter.
Why can I set much lower sampling frequency of a signal and it still looks correctly?