I wondering something. While working with adalm pluto sdr in gnu radio, the sample rate I enter in the source block is actually bandwidth. I know that bandwidth must be half of the sampling rate because of the Nyquist rate. How can GNU radio taking a 4MHz sample rate and 4MHz bandwidth.Also, can we sample 20 MHz bandwidth with 4 MHz sampling rate in GNU radio with pluto sdr? Because in continuous RX mode max sample rate of adalm pluto is 4-5 MHz.
Software-defined radios do quadrature sampling: every sample is actually two, a real (in-phase) sample and an imaginary (quadrature) sample. That's why sampling rate is equal to the bandwidth.
You can't sample a signal with bandwidth 20 MHz at 4 MHz; doing so would introduce lots of aliasing. The maximum signal bandwidth you can sample at that rate is 4 MHz (theoretically) and more likely around 3 MHz, depending on the performance of the filters and converters in your receiver.