[Laser] Recent NLOS experiments using IR Leds

[Paul Cianciolo]

Kerry,
Great work!!

A couple questions.
How far to the optical horizon, or what is the first optical obstacle that
you encounter on the transmit end?
Also what is the terrain like in between you guys?

Were the receive and transmit pointing both broad, as far as pointing?

Also what freq was the PSK on?

PauLC
W1VLF

-----Original Message-----
From: laser-bounces at mailman.qth.net
[mailto:laser-bounces at mailman.qth.net]On Behalf Of Kerry Banke
Sent: Sunday, April 27, 2008 10:39 AM
To: Free Space LASER Communications
Subject: [Laser] Recent NLOS experiments using IR Leds


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

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