Re: [Discuss-gnuradio] Direct ADC for Quadrature Demodulator

[Chris]

Radio Dev wrote:
> Using DMA mode, the sampling rate will be 30MHz,  and seems enough fast
> (>2x10.7MH).
> The problem is band width.
> When IF signal has a band width < 4MHz,  the sampling rate will be enough,
> i.e. 30MHz > 2x(10.7+4)MHz. Dangerous but it works.
> When IF signal has a band width > 5MHz,  the sampling rate will not be
> enough, i.e. 30MHz < 2x(10.7+5)MHz. Can not work.
>
> Did I have a proper right understanding?

I believe you will find the concept of subsampling helpful.  The basic 
idea is, under certain conditions, you purposely undersample at a rate 
determined by the intelligence bandwith, not the IF center + bandwidth. 
Google returns a number of reasonable hits on the topic so I won't quote 
links here.