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

[Kerry Banke]

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 -