[Discuss-gnuradio] Fundamental question on Sampling rate

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Dear All,

 Mine is more of a fundamental question.

I have a 50 MHz (3 db bandwidth) wide QPSK signal. 

I am aware that Gnuradio blocks can not be used for real time decoding.

In order to record the signal and demodulate it correctly, what should the minimum sampling rate be? 

 If the minimum sampling rate is 100 MSPS, then I am pretty much stuck with USRP x310 as the only selection available.(or maybe LIMESDR-PCIe)

I am also not sure  if the source block streams 100 MSPS sampled signal or I+Q (50 MHz-I, 50 MHz-Q).

Thank you in advance.