[Laser] Re: Troposcatter and Information Theory-2

[Walt Rauscher]

Hi all,
	I like reading all the discussions here and the ideas. However the proof is
in actually using and measuring the results. I have built some LASER
modulators and receivers that will accept any audio (soundcard). I did some
tests using a simple photodiode detector (not very sensitive) and place an
attenuator over the diode (sheets of paper) to reduce the signal (laser
light bounced off the ceiling). I tried several of the digital modes as well
as fast and SLOW CW. Of the digital modes PK31 was the best (copied the
weakest signal, it was a good bit better than JT44 (that surprised me). But
the very slow CW (from ARGO) was copied on the weakest signal. I can't give
actual numbers as I don't have my notebooks here.
	As someone pointed out, there can be a difference between LASER and RF,
although there also may not be. Some the the modes developed for RF includes
redundancy to account for fades (get enough data across in a short time,
repeat the data and hope that the signal is strong enough sometime). This
also applies to what the LASER path is. A LOS path probably doesn't fade so
redundancy isn't needed, cloud or tropo-scatter could. More experimentation
is needed to determine what may work best. With a soundcard and all the free
software available many modes can be tried without any changes to the
hardware (LASER modulator/detector).
	Just some observations and thoughts.

Keep on experimenting,
	walt

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