[Laser] Progress with NLOS IR laser scatter project

[Kerry Banke]

Last night we ran the first try at an experiment to detect a  1W, 910 nm 
laser at a NLOS location about 3 miles away at the home of Greg Bailey, 
K6QPV. The result was a signal 30 dB above the noise.   The laser beam has 
been expanded to about 4 inches for safety as well as to provide a larger 
area for scatter.  The laser was one of several I purchased off a web 
auction for less than $15 & was  powered by a 50% duty cycle square wave at 
172 Hz.  The elevation to the horizon from the Tx side was about 5 deg so 
the laser was elevated to about 7 degrees. The horizon was a tree & home 
covered ridge between the two locations.   The signal was detected using a 
4" lens ahead of a K3PGP style Pin detector with MPF102 amp & no bias 
resistor. The detector diode is rated at 10 pF capacitance with no bias & 
1mm square active area. Speclab software was used to detect and display the 
signal which was easily found within a couple of minutes as the path had 
been fairly carefully plotted on a map.  The receiver was pointed just 
above the horizon in the direction of the transmitter so I guess  this is 
really forward scatter rather than back scatter.  I believe the optics on 
the Tx end is far from optimal so I need to work on that. The next step is 
to try actual communications using Andy's LaserScatter software.
I have a Jpeg screen capture available I can send. I'll also have a picture 
of the Rx setup during the test soon.
  - Kerry N6IZW -