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

Hal Murray hmurray at megapathdsl.net
Mon Jun 1 22:52:48 UTC 2009

rmoncur at bigpond.net.au said:
> 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. 

Sounds like a fun project.

Do the clouds shift around enough to cause Doppler problems?

You might find something in the way of a DSP or FPGA demo board.  (I don't 
have any suggestions.)  Or maybe a demo board for an audio chip.

How stable is the osc on your current board?  Do you need accuracy or 

Can you feed a calibration signal in the other stereo channel and sort it out 
in software?

Or tap off some signal in the board and feed that to a counter for 

These are my opinions, not necessarily my employer's.  I hate spam.

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