[Laser] Optimizing sound card modes for optical communication

[Chuck Hast]

On 11/21/06, Art <KY1K at verizon.net> wrote:
> GPS time sync'ing is not nearly as expensive as it used to be.
>
> If you use the NMEA output on a consumer grade GPS, you can get
> accuracy of 100 milliseconds.
>
> For 50 nS accuracy, you need a known good gps module with a 1 PPS output.
>
> Expensive Oncore timing GPS units are selling on ebay for $30 to $45.
> Although they have solid performance, many of the OEM timing modules
> are MUCH cheaper and just as accurate.
>
> My Superstar II GPS board cost me $4. on ebay and I wish I had bought
> more of them, I'm so glad I didn't buy the higher priced Oncore units.
>
> GPS timing is not nearly as expensive as it used to be and shouldn't
> deter anyone who wants to use it for communications.
>
> More can be done with less, forsure!!! But, let's not lose sight of
> the benefits of accurate timing because it used to be expensive. Most
> of the accurate timing boards available today are pulls from working
> cellular sites. There's nothing wrong with them, and newer units are
> not necessarily any more accurate.

What about the use of plain old OOK? it is simple and easy to implement,
I know that you are at the mercy of noise when the optical carrier is off,
but using the GPS on each end to discipline things should allow the
system to use the timing to determine when it should look and using
nice narrow filters you should be able to reduce the background noise
a good bit. between good data you could send some form of idle data
so that the RX has something to also synch to.


-- 
Chuck Hast  -- KP4DJT --
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."