[Laser] Recent NLOS experiments using IR Leds

[Kerry Banke]

Last evening K6QPV and I  completed our first NLOS one way contact using an array of 200 IR Leds at a distance of about 3 miles.  The weather conditions were clear skies with some haze. The LED array was sending PSK31 text of N6IZW DE K6QPV which was received with essentially perfect copy when the stobes of passing airplanes did not interfere.  Unfortunately the NLOS path is in line with the landing pattern for a local airport.  The Tx array power input is 17V at 2 Amps peak. The Leds are of the type used for IR remote controlsoperating in the 940 nm region. The Tx array is pinted at the optical horizon towards the receive site. The receiver is a 7mm area pin photo diode in the K3PGP configuration and has a 730 nm long pass filter in front to reduce unwanted light interference.  The receive optics is a 12" microwave dish covered with Aluminum tape.  This appears to work  much better in picking up a broad area signal than the 5" glass lens system I have.  The pointing is
 very non critical as the Leds have a 40 deg beamwidth and the scatter is over a broad area on the horizon. 
  When sending a pure tone the signal was about 15 dB above the noise in a 1 Hz BW. 
   
  Kerry N6IZW in San Diego