Re: [Discuss-gnuradio] Differences in Signal Spectra between Daughtercards

[Eric Blossom]

On Mon, Jan 11, 2010 at 08:58:16AM -0800, Thomas wrote:
> Hi,

> I'm working on a project that requires using two receivers tuned the
> same frequency simultaneously. Ideally, I would use identical
> receivers, but I am using a TVRX card and a DBSRX card becuase those
> are what I have available.

> I'm curious why the spectra of signals received with the TVRX seem
> to be more spread out than with the DBSRX. An example is shown in
> the link below. The upper plot is from the TVRX, and the lower plot
> is from the DBSRX. This signal happens to be an ATSC carrier. Both
> daughtercards are tuned the same frequency, and the FFT parameters
> and so forth are identical.

> http://img23.imageshack.us/img23/3206/screenshotusrpfft2.png

> Does anyone know what causes this apparent spreading and if there is
> anything I can do about it?

> I purposely left out details of my configuration to keep this
> message short, but feel free to ask for more information if this
> isn't enough to answer my question.

> Thank you,
> Thomas

Try setting the gains differently on the two boards.

Eric