[Linrad] Re: Linrad-SDRIQ Clock Speed

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Guy,

> I have recently updated my Linrad-SDRIQ web pages at
> http://www.vhfdx.radiocorner.net/LinradSDRIQ.html
> along with the linked pages of my parameter values and notes on those
> parameters.
Good:-) 

> The sampling rate of the SDR-IQ is nominally 66.666667MHz,
> and when decimated by a factor of 700 for the Linrad-MAP65IQ
> combination
> this leads to a sampling rate close to  95238Hz.
> 
> My SDR-IQ actually runs a little fast, by about 800Hz, so I am using a
> value of -800Hz for SampleClockAdjust.
> This doesn't actually change the clock frequency of the SDR-IQ, but it
> certainly makes Linrad read correctly!
> I note that the file par_userint holds a value for "Rx ad speed" of
> 95236, and that this value changes
> according to the value of SampleClockAdjust - it is 95238 with zero
> adjustment applied.
OK. This is the data rate Linrad should expect.

> I also see that the file par_ssb holds a parameter "A/D speed" equal
> to 95236, and that this value does not seem to change with the value
> of SampleClockAdjust. What is this, how is it different from "Rx ad
> speed", and why is (nearly) the same value stored in two separate
> files?
> 
> Just curious!
Good reason to ask:-)

The similar value in par_ssb is (was) used to check that the file really
was saved for hardware configured to run at that speed. When the
speed difference is above limit (1% or so, do not remember) you
should be prompted to the parameter setup routine. 

As it turns out, this test no longer works, so now the user may 
enter receiving from a soundcard at 48 kHz with parameters
that were set up for the Perseus at 2 MHz. Might be ok, but the 
other way around would likely cause the system to hang. When running
at 2 MHz one has to be careful about cpu load.....

I will put the test back.

  73

 Leif / SM5BSZ



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