[Laser] 21 mile daytime laser contact durin ARRL 10GHz & Up contest

[James Whitfield]

It is good to hear of your success.

>From the 50 dB over the noise level, can you estimate what distance you
might have been able to establish communications?

I assume that you were using on-off keying of the laser at 755 Hz.  Did you
observe harmonics at 2265 of the square wave?  Perhaps if you recorded the
sound you might be able to attempt to decode the signals.  It might not
demonstrate anything but the audio bandwidth of your system, but I am
curious.

Best of luck to you and Lee on your continued experiments.

James
 n5gui


----- Original Message -----
From: "Kerry Banke" <kbanke at sbcglobal.net>
To: <laser at mailman.qth.net>
Sent: Sunday, August 19, 2007 5:43 PM
Subject: [Laser] 21 mile daytime laser contact durin ARRL 10GHz & Up contest


Yesterday Lee, KD0IF and I made a mid day laser contact over a distance of
21 miles near San Diego  as part of the ARRL National  10 GHz and Up
contest. Last year we did a 7 mile daytime contact but experienced very
heavy scintillation which we have found to be typical for warm weather in
the San diego area.  This year we added narrow wavelength optical bandpass
filters ahead of our optical receivers and are using a fast AGC provided in
the Spectrum Lab software.  This was our first two way  daytime
communications  tests with the filters. The scintillation on the raw signal
appears to be very minimal compared to our contact last year. We don't know
if the narrow optical filters have provided this improvement or if we just
had unusually  good conditions so we need to do more daylight tests with and
without filters for comparison. The filters are at 920 nm with a 30 nm half
power bandwidth. When operating at high power with  1W  collimated to  a 4"
dia beam, the laser
 transmitters delivered  signals that  were a stable 50 dB above the noise
in a 1 Hz BW at 21 miles.   Communications was done using PSK31 with a
center frequency of 755 Hz.
  Does anyone know if adding the  narrow optical filters should reduce
scintillation? Thanks also to Greg, K6QPV for assisting with the contact.
   - Kerry N6IZW -
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