[Laser] Sky illumination experiment

[Kerry Banke]

Last evening I finally got around to trying an experiment I have been 
wanting to do for some time.  I have a 1 KVA  Elgar variable frequency AC 
power supply I borrowed from Greg, K6QPV.  I hooked it up to a two tube 48" 
florescent light fixture that I laid on the ground upside down, pointed 
skyward.  I set the supply frequency for 55 Hz which produces a primary 
light modulation at double that or 110 Hz.  I used my laptop running 
Spectrum Lab with a 1 Hz bin and displaying 100-150 Hz.  The receiver 
was  my standard K3PGP low light unit with a 4" lens. The sky was clear 
with a slight bit of haze detectable when viewing hills at 2-4 miles away . 
This is about as clear as San Diego skies get this time of year.   I went 
to a NLOS location about 1/2 mile away and swept the horizon in the 
direction of my home.  I was able to detect the 110 Hz signal over maybe 10 
degrees Azimuth & elevation. As seen in my NLOS Laser experiments, the 
clear sky signal is maximum at the horizon towards the source. The signal 
was only about 5-10 dB above the noise but was easily identifiable.  This 
was the first step towards trying a higher power experiment with hopefully 
a 400 W Sodium Vapor lamp. The estimated light output from the florescent 
tubes is about 5600 lumens ( assuming about 70 lumens/watt for two 40 watt 
tubes.  400 watts of High Pressure sodium vapor lamp could provide around 
40,000 lumens and if I can be lucky enough to find a  400W Low Pressure 
Sodium lamp, up to 72000 lumens. This approach should allow communicating 
with any of the multi-tone communication programs.
  - Kerry N6IZW -