[Laser] Optimizing sound card modes for optical communication

[TWOSIG at aol.com]

Art

Thank you.

I very much like  full duplex.  I would also point out that the light 
communication record of  167 KM was done full duplex, simple amplitude modulation, 
without lasers.   Their equipment had no apparent problem with backscater.  They 
did use  telephone style handsets so that they did not have a feedback loop 
from a  speaker into the microphone.

I am sure that gps timing accuracy, slower  data rates, and narrow bins will 
provide fantastic results.  I look forward  to hearing about activities using 
them.  Still, I think there is a lot more  that can be done with less 
sophisticated technology.  ( Perhaps I see too  many dollar signs when I think of 
precision gps clocks.  More likely, I  just don't have the imagination to see what 
can be done with them. ) My life  experience is more apt to "see" the current 
state as suffering from using 16th  century telescopes.  

Of course I am also biased:  I want  "them" to plant an optical comm beacon 
or downlink on a Moon probe that can be  seen with 10X50 binoculars and the 
data decoded with my home computer interfaced  to a $100 module that slips in 
place of the eyepiece of mys 114 mm F/8  Newtonian.  Wouldn't that get bunches of 
people around the world interested  in Space, telescopes, and electronics?

James
N5GUI



In a  message dated 11/21/2006 5:46:48 PM Central Standard Time, 
KY1K at verizon.net  writes:
James, I couldn't agree more!

Warmed over radio modes aren't  going to give much advantage on laser, 
and in general, we should be rolling  our own.

MT63 is a possibility, although it needs to be modified for much  narrower 
bins.

I asked K1JT to give us a narrower bin version of WSJT,  complete with 
the timing and repetition cycles to reinforce the previously  sent 
message during the same sequence, but he has not seen fit to write  
the code. Since his program uses some proprietary code from a second  
source, he cannot release the source code. But a specially built WSJT  
communications protocol seems most ideal to me...if we could make it  happen.

Laser modes need to be much narrower bins with slower throughput  and 
need to take advantage of precision timing (since the time of flight  
of the laser is much shorter than typical HF paths). I just bought 
some  OEM gps units on ebay ($4 each) that offer 50 nS timing error, 
which is  about as good as it gets (even the famous Oncores barely do 
that  well).

Furthermore, since the best performance in laser happens on  baseband, 
the tones do not shift because we don't 'tune' the receiver. So,  
500.0001 Hz at the transmitter will equal 500.00001 Hz when it comes 
out  of the receiver.

Advanced laser modes for extreme weak signal work should  utilize GPS 
time sync and/or  the presence or absence of a discrete  frequency to 
make a 1 or a zero and be done in baseband only.

And,  once factor very much overlooked in Lasercomm is the 
practicality of full  duplex.  Sure, we are going to detect our own 
signals on backscatter,  and they will be big signals....But, the 
receiving station has the ability  to reject the backscattered signal 
because it is on a different frequency  than the transmitted signal. 
So, why not do full duplex??

Keep 'dsm  lasers lit.

Art