[Laser] One way 3 mile laser NLOS contact using PSK31

[John Matz]

Congratulations ... getting close to a two-way QSO ... makes me think about
trying NLOS with visible light.  Scatter should be better at higher freqs?

BTW, I have been looking into IR propagation at 1400 nm.  Higher power at
those lower freqs ... I'm told ... is relatively "eye-safe" because the
cornea/lens is opaque and doesn't focus the IR light to a small spot on the
retina. If so, I wonder how it is for scatter.  Maybe haze / water droplets
are sufficiently flat to scatter that freq / wavelength well too?

John Matz KB9II

----- Original Message -----
From: "Kerry Banke" <kbanke at qualcomm.com>
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Sent: Monday, December 13, 2004 9:41 AM
Subject: [Laser] One way 3 mile laser NLOS contact using PSK31


> Last evening Chuck (WB6IGP) & I made our first one way NLOS laser contact
> using PSK31 between our homes which are about 3 miles apart. The 1W 910 nm
> laser with 4" beam expander was located at my home and precisely pointed
in
> the azimuth  direction of Chucks home and a couple of degrees above the
> horizon.  There was slight haze which I have found to be great for
> producing scatter signals.  At Chuck's home the 260 Hz carrier was readily
> audible using the 4" lens ahead of the K3PGP pin detector/preamp
> configuration.  Looking at the signal with SpectrumLab showed the carrier
> to be steady at about 35 dB above the noise with a 1 Hz BW. A test message
> was sent with perfect copy. The narrow  laser beam could be followed with
> the detector over maybe 30 degrees elevation  with the signal slowly
> increasing towards the horizon. In this case we were limited near the
> horizon by a Sodium vapor street lamp so could not view the bottom maybe 5
> degrees.  My recent propagation experiments have shown the following with
> this configuration:
>
> On totally clear, cold nights following a rain, there is no useable
scatter
> at 3 miles out (at least for levels required for PSK31) . Most
> evenings  there seems to be a cone of useable signal  for both back
scatter
> and forward scatter with the signal dropping off as the receiver
approaches
> 90 degrees to the transmit beam. Of course clouds produce an amazingly
> strong spot or line. Light rain  also produces great scatter.
>
> The next step is to finish the equipment to do a two way contact. Chuck
has
> assembled a second  working receiver & I'm in the process of building a
> second  laser transmitter. We'll then be ready to see what kind of two way
> distances are possible and will also try the LaserScatter software as the
> hardware has been built with this in mind.
>   - Kerry N6IZW -
>
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