Re: [Discuss-gnuradio] A/D Output

On 09/30/2010 02:38 PM, Sharif Shaher wrote:
> Hello,
>
> I am using gnuradio and a usrp2 to capture samples (shorts) to a file,
> that is 16 bit I and 16 bit Q.
> I looked at this data in matlab and noticed that in many instances the
> samples exceed 13 and 14 bits
> for both positive and negative numbers (ie -12567 or +12989).
>
> I was under the impression that a 14 bit a/d meant 13 bits plus a sign
> bit so max 8191, min -8191.
>
> Should I expect this behavior, am I interpreting something incorrectly.
> If this is expected
> can someone please explain. I though the rx_gain was applied before the
> a/d so the max
> output would be be 13 bits plus a sign bit.
>

You are seeing the effect of the digital down conversion in the FPGA,
which includes scaling, and shifting, and filtering.

-Josh

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