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Re: [Discuss-gnuradio] ADC sampling window

From: Brian Padalino
Subject: Re: [Discuss-gnuradio] ADC sampling window
Date: Wed, 9 Jun 2010 21:53:06 -0400

On Wed, Jun 9, 2010 at 8:27 PM, Roberto de Matos <address@hidden> wrote:
> Hello,
> The maximum sampling window of USRP2's ADC is 50MHz or 100MHz?
> Because of Nyquist Theorem the straight answer is 50MHz, once the ADC runs at 
> 100MHz. However if we use the complex samples (quadrature sampling) the 
> answer is 100MHz.
> So, which is right??

Nyquist states you need a sampling frequency of 2x the bandwidth of
the signal you are sampling.

When you do real sampling, you are able to accurately sample a
bandwidth of [0,Fs/2].  With baseband IQ sampling, you are accurately
able to sample a bandwidth of [-Fs/2,Fs/2].  Note you did not gain any
positive frequency content, and only negative frequency content due to
knowing the phase of your signal now.

Hopefully this clears up your confusion.

> Thank you,
> Roberto de Matos


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