[Laser] Re: Troposcatter and Information Theory-2

[John Matz]

----- Original Message -----
From: "Walt Rauscher" <wrauscher at gamry.com>
To: "<font color=red><B>== Free Space LASER Communications ==</font></B>"
<laser at mailman.qth.net>
Sent: Friday, July 02, 2004 8:35 AM
Subject: RE: [Laser] Re: Troposcatter and Information Theory-2


> 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
>
> http://mailman.qth.net/mailman/listinfo/laser
>
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