> -----Original Message----- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@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... _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.