[time-nuts] Sound Cards for locking to GPSDO 10 MHz references
Lux, James P
james.p.lux at jpl.nasa.gov
Mon Jun 1 23:06:42 UTC 2009
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Rex Moncur
> Sent: Monday, June 01, 2009 3:00 PM
> To: 'Discussion of precise time and frequency measurement'
> 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 readily locked to either 10 MHz or if necessary to
> some other frequency that we can 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 internal 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
Some of the "pro" sound interfaces have a "word clock" input.
There are a variety of things that take a external input and generate a S/PDIF that's properly timed, as well. Lots of boxes will take a S/PDIF sync input (e.g. the Edirol FA-66 which was used by lots of Flex-Radio folk), so maybe that's something you could easily generate from your 10MHz.
A chart at Cakewalk shows that MOTU has a USB interface (828MkII) which has a word clock sync. It's going to be a pricey beast though, with 8in/8out ($800?)
Even if you have a word clock input, you're going to have to synthesize that from the 10 MHz. Maybe it's easier to just make a S/PDIF which is a MUCH more common sync signal. ( I think S/PDIF is something like 3 MHz)
The HPSDR folks also might have something...
More information about the time-nuts
mailing list