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Re: [Discuss-gnuradio] Funcube dongle issues and a solution

From: Alexandru Csete
Subject: Re: [Discuss-gnuradio] Funcube dongle issues and a solution
Date: Wed, 30 May 2012 12:01:59 +0200

On Wed, May 30, 2012 at 8:51 AM, Gasper Zejn <address@hidden> wrote:
> Hi,
> I was using Funcube dongle and found a strange bug. Whenever I used the FCD
> source in my flow graph and started the flow, the (demodulated) signal came
> out corrupted. However, if I then just started qthid, it would correct itself
> and could see bits in waveform perfectly well. This was happening with
> different firmware versions.
> With a bit of experimenting in the earlier out of tree gr-fcd, I found out
> that reverting two commits[1][2] resulted in resolving the issue.
> I've made changes to in-tree gr-fcd and recompiled and it's now working in a
> way, but issues remain. One is setting frequency at runtime (via a variable),
> where FCD flips back into spitting out corrupted waveform.
> This is where the problem outgrows my knowledge.

Hi Gasper,

Sounds to me like you are having some interference on the frequency
you are trying to use. Or maybe your are using the center of the
passband where we have a strong DC peak. I'm only guessing since you
don't give any details about your setup, e.g. what modulation are your
using, and how do you determine that your signal is corrupted.

The FCD source block in the master branch appears to work correctly
and I have no issues demodulating narrow band FM. I have no setup to
try digital modes. The commits you refer to are necessary for correct
setup and tuning of the FCD. If you revert them the FCD may not have
the correct initial setup or may have the settings from the last time
you were using it.

As said, I suspect you have some noise or interference in your filter
passband. Please provide more details about your setup, flowgraph,
etc. I found that plugging the FCD directly into the PC is a bad idea
causing strong interference. Always use an extension cable and
preferably also a USB hub between PC and FCD.


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