[time-nuts] Sound Cards for locking to GPSDO 10 MHz references

Alan Melia alan.melia at btinternet.com
Mon Jun 1 22:29:44 UTC 2009

I have seen it talked about (around the LF fraternity, but generally they
are stable enough there and just need calibation) a lot but not accomplished

How about injection locking the on board osc....maybe gating the feedback
with the reference....note I havent tried this? Another technique I have
used to shift "logic-block" oscillators is to vary their supply voltage,
they will oscillate from around 3v to well over 5.5v ....that might enable
you to phase lock it  using a variable regulator to vcxo to crystal??

Alan G3NYK

----- Original Message -----
From: "Rex Moncur" <rmoncur at bigpond.net.au>
To: "'Discussion of precise time and frequency measurement'"
<time-nuts at febo.com>
Sent: Monday, June 01, 2009 10:59 PM
Subject: [time-nuts] Sound Cards for locking to GPSDO 10 MHz references

> Hi all
> Does anyone have any experience of locking a USB external soundcard to a
> GPSDO 10 MHz reference.
> I am interested in advice on any good quality soundcards that can be
> locked to either 10 MHz or if necessary to some other frequency that we
> derive from a GPSDO source.  I have done some tests with the SignalLink
> soundcard that uses a Texas Instruments PCM2904 chip and requires a 12 MHz
> lock frequency.  This requires some cutting of tracks to remove the
> oscillator feedback and insert the locking frequency.  12 MHz is readily
> derived from 10 MHz but I have not been able to get it to lock.  The Texas
> instruments data sheet suggests that it is possible to use an external
> refernce but also says this is not recommended.  With this expereicne I
> would rather find a sound card that is designed for external locking that
> does not require the cutting of tracks.
> For info the purpose of this request is that we are looking at using very
> narrow bandwidth modes at less than 1 mHz for light wave communcation.  To
> date using LEDs and cloud reflection we have worked over 200 km with WSJT
> but we should be able to do 20 dB better if we can get down to milli-Hz
> bandwidths (at the expense of spending all night to complete a QSO). Our
> expereince to date is that standard sound cards are just not stable to
> better than 5 milli-Hz at 1000 Hz which should be readily solved by GPS
> locking let us get down to sub milli-Hz levels.
> Rex VK7MO
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