[Laser] Simple optical beacon experiment in San Diego

[Kerry Banke]

We have installed a simple LED optical beacon on San Miguel Mt. in San 
Diego. The beacon is a Luxeon 1W red LED with 15 Degree (30 deg 
total)  integrated lens.  It is powered by a square wave at about 700 Hz 
and has an identification of N6IZW once each minute.  At 8 miles the beacon 
was  visible through a 7X20 mm  rifle scope mounted on my K3PGP type 
receiver with 4" glass lens.  The tone was barely detectable by ear as 
there are several lights on the same mountain generating huge quantities of 
60 Hz and harmonics.  Using Spectrum Lab SW on my laptop,  the tone was 
readily observed and disappeared during the identification period.  The 
tone strength was only slightly stronger than the 720 Hz harmonics ( 12th 
harmonic of 60 Hz probably due to receiver overload) of the other lights on 
the hill. The frequency response of the receiver  currently extends down to 
a few tens of Hertz so is very much affected by 60/120Hz lights. Adding a 
good high pass filter to the front end should make the beacon much easier 
to copy. Thanks  goes to Greg, K6QPV for putting the beacon up on the hill 
and setting it up with a control link to turn it on & off.
  - Kerry Banke N6IZW -