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

From: Thomas
Subject: Re: [Discuss-gnuradio] Differences in Signal Spectra between Daughtercards
Date: Tue, 12 Jan 2010 10:46:55 -0800 (PST)

I've tried different gains on both boards, but it doesn't make a difference. The frequency I am tuning to is 560.31 MHz, which is below the specified frequency range of the DBSRX. My DBSRX tunes to that frequency without any errors, but perhaps tuning it out of range it is causing a problem. I will try to compare with a spectrum analyzer to see which card is giving the most accurate representation of the signal.



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.


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