[time-nuts] GPSDO project (SDR)

Dave Baxter dave at uk-ar.co.uk
Mon Jun 29 11:48:28 EDT 2009


Hi Brad.

Just catching up with this, after a hot weekend, and doing "White Van
Man" impressions on (an even hotter) M1 this morning...

Personally, I wouldn't bother with any high accuracy clock/oscillator
for the SDR, unless you can also synch the AD sampling clock in the
soundcard.  As that will have much more of an effect on carrier
frequency generation/indication etc than even an undisciplined
oscillator in the SDR mixer itself.

Then there is the issue of just how accurate is the software in it's DSP
routines in interpreting the (sampled) data from the soundcard.   Much
SDR software has a "frequency calibration" function, as it is well known
that most consumer soundcards are not that accurate in their timing, not
just that the RF>I/Q mixer clock is often off a bit.  Even some of the
96k sampling 24 bit "golden ears" types can be somewhat wayward.

Have you also ascertained that Power SDR run's OK on Vista?   Only ask,
as I know that others have found "Big" trouble with much SDR software,
and the way it tries to use the PC's sound system, and how that
interacts with Vista's way of doing things.   I've not run Power SDR
myself on anything other than demo files on XP/2000 by the way.

Vista's background timekeeping is crap too I'm told, quite how that will
impact SDR software though, I do not know.

Check out the SDR lists on Yahoo, their maybe people there who have done
what you describe, but I also monitor those lists too, and can't recall
anyone doing that (GPSDO) thing with the mixer osc'.  Though there has
been much discussion about soundcard sampling clocks!
http://groups.yahoo.com/group/softrock40/join
Also the KGKSDR list, the address of escapes me at the moment.  There
are probably others.

Wonder if anyone has integrated "ClickLock" into any SDR software yet...

73.

Dave G0WBX.


> -----Original Message-----
> In a message dated 28/06/2009 20:34:25 GMT Daylight Time, 
> brad at braddye.com  
> writes:
> 
> I have  just purchased a Thunderbolt GPS receiver. I hope to 
> use this  
> to  discipline an oscillator on 66.66666 MHz so I can use it 
> as a LO on   
> my Software Defined Receiver (SDR-IQ).
> 
> Building such an oscillator  is a little over my head so I thought I  
> would ask the group if  anyone knows where I could buy the 
> missing link  
> of this project. I  have put a drawing of my project on the 
> web showing  
> the specs of  what I need. The oscillator is shown in the blue box.
> 
> Any help or  suggestions would be greatly  appreciated.
> 
> http://www.braddye.com/gps_do.html




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