[linrad] SDR-IQ and Linrad

[Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>]

Hi Dave,

Dave Blaschke wrote:
> K1JT wrote:
>
> > In principle, any hardware that can be made to work with Linrad should 
> > also be usable with the Linrad-MAP65 combination.  At present this is 
> > true only if the sampling rate can be set to 96.000 kHz (four 
> > channels, two I-Q pairs) or 192.000 kHz (two channels).  If you want 
> > to try MAP65 and don't have xpol, a simple way to get started would be 
> > to put nothing into the Y channel (or perhaps put the X signal into 
> > both X and Y inputs).  I have tried this in my station and it works -- 
> > although of course no polarization information is produced for the 
> > received signals.
> >
> > The SDR-IQ can provide effective I-Q sampling rates of 55.555, 
> > 111.111, 158.730, and 196.078 kHz for a single polarization.
>
> For some reason my post to "Linrad mailinglist" 
> <linrad@xxxxxxxxxxxxxxxxxxxxx> is bouncing.
>
> I'm using SDR-IQ. Is it a certainty that the SDR-IQ cannot handle 
> sampling rate values outside those shown above; such as the 96.000 kHz 
> required by MAP65?  I would like to test this. (Or am I misunderstanding 
> the requirements?)

I don't have an SDR-IQ or any of its documentation, but as I
understand it the A/D sampling rate is fixed at 66.667 MHz.
 Resampling and decimation is then done in a specialized
chip (by Analog Devices, I think).  I imagine this means
that only certain output sampling rates are possible -- ones
related to 66.667 MHz by the ratio of small integers.
Perhaps someone else with better knowledge of the SDR-IQ can
correct me, or otherwise elaborate.

> I can see how to set the sound output sampling rate under Linrad to 
> 96.000 kHz, but how does one manually set the sound input sampling rate 
> to this value? Or is a pre-programmed value chosen by Linrad whenever 
> SDR-IQ is selected as the input device during setup?

When you use the SDR-IQ with Linrad you don't need a Delta44
or any other soundcard for input.  A/D conversion takes
place in the SDR-IQ, so the input sampling rate is
determined there.  As I mentioned above, the SDR-IQ also
does decimation to provide a smaller bandwidth (190 kHz or
less) at its output.  The output from SDR-IQ (input to
Linrad) is digital, not analog.

> My second question: Has a revised version of Linrad been released that 
> will detect the SDR-IQ under Linux? I am currrently running the Windows 
> version.

I expect Leif will correct me when he returns home, if I am
wrong about this.  I believe the most recent version of
Linrad (both Windows and Linux) can always be found at the
bottom of this page

	http://www.sm5bsz.com/linuxdsp/linroot.htm

along with a brief description of changes from previous
versions.  The most recent (stable, released) version can be
found on the Linrad Home Page:

http://www.nitehawk.com/sm5bsz/linuxdsp/linrad.htm

	-- 73, Joe, K1JT


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