[Laser] New San Diego optical beacon

[Art]

Paul,

I never did good documentation, so I hesitate to publish anything 
about my effort....but.....

Some number of years ago, I got some very nice photomultiplier tubes 
and cockcroft-walton power supplies from ebay.

One evening, I set up a crystal controlled green and red pulsed LED 
in my dooryard (standard used LED's from consumer electronic scrap, 
nothing special). I didn't overdrive them, I ran each at 50 ma with a 
50 percent duty cycle.

I threw the laptop in the car (with the tube strapped the roof rack 
with duct tape) and proceeded to drive in a 10 to 12 mile loop around 
my house with the pm tube pointed straight up (no lens). There was no 
lens to gather light, just a few holes that line up with the tube, so 
it only saw the sky overhead.

The sky was very clear that night, there were zero clouds.

I expected I'd lose the signal at the end of my driveway, about 700 
feet from the house......

I used my ear only and the computers audio amp output, no fft or 
anything fancy.

I drove around the loop and was amazed that I could hear it almost 
anywhere!!!! At 5 miles distance, it was Q5. Towards the 10 to 12 
mile distance, it was EME weak-but there all of the time.

I was fairly stunned-but never had time to repeat the experiment.

The experiment ended abruptly when I forget to cover the PMT as I 
drove through an intersection with a streetlight, and I flashed the 
tube. So, my plans to compare the readability of red vs green never 
happened and I never got back to playing with that setup again.

Regards,

Art



At 04:30 PM 1/22/2007, you wrote:
>I'm interested reading this... a while ago I made a pcb with 230 
>very!!! bright white leds, I used white because I got them cheap 
>from ebay! I planned to use it as a beacon from my house and shine 
>it straight up sending slow Morse modulated at about 400Hz, then 
>drive away to some high spots around and see if I could pick it up....
>I also made a 4" receiver and preamp using the K3PGP design and a 
>TBA820 op amp into the phones and laptop.
>Up till now I never did get round to doing this, but if anyone else 
>has tried this i would love to hear and spur me on to get it done for myself.
>Thanks Paul Tomlinson M0EME
>