Re: [Discuss-gnuradio] Patch to Include LNA enhancement and IF gain and filter settings for FCD

[Alexandru Csete]

On Mon, Jun 11, 2012 at 6:21 PM, Bryan Biedenkapp <address@hidden> wrote:
> Hi All,
>
> I've created a patch based on the gnuradio-3.6.1git sources to include extra
> options for the FunCube Dongle on GNU Radio. I'm not sure of the policies or
> procedures for posting a patch to the group for review (new to this group).
> So, I have attached the patch as a file.

Hi Bryan (and others),

Thanks for your patch. I will review it as soon as I can, however,
before I do that I would like to ask you and others whether we really
want all this functionality.

The reason why these API calls weren't included in gr-fcd from the
beginning is very simple: In my 1.5 years working with the Funcube
Dongle, I have never needed to adjust anything else than the
frequency, I/Q corrections and LNA gain. I remember we have spent a
lot of effort implementing the full API in Qthid, then got very
disappointed to see that the default values were always the best ones
and most controls didn't even have any practical effect. Now I still
have to maintain these functions in qthid, check that they still work
with new firmware releases, etc. and for what use?

I can imagine the LNA enhancement to be of some use so I guess we
could include that without further discussions.

Concerning the IF filters: They are by default at their narrowest
setting, which is 1 MHz and 2.15 MHz. The bandwidth of the FCD is 96
kHz. Is there any practical reason why anyone would want to increase
the IF bandwidth?

Similar argument for the IF gain settings: They are by default set to
have lowest gain and with these settings the FCD has sufficient
sensitivity. IMHO increasing the IF gain would not result in improved
receiver performance, as the FCD already suffers greatly from lack of
bandpass filters. Someone with more RF knowledge than myself may want
to comment on this, here is a diagram of the RF chain:
https://github.com/csete/qthid/blob/3.x/images/rfchain.png

If any other Funcube Dongle owners have different opinion or
experience, let us know!

Ultimately, the decision is not mine, but I think we should decide how
much of the FCD API we want to include and maintain.

Alex