[Laser] New Cloud bounce system being built Optical detectors

Sun Jul 17 14:23:20 EDT 2011

Tim,

This is my philosophy on illuminating clouds  for CB.
Its always a compromise.

With LED's, let's say 40 degrees wide or so I would think that by the time
the beam hits the clouds the beam is very weak.
But you have the advantage on the receiver side of not having to aim
critically, and also covering such a large area of the clouds the
probability of energy being directed toward the RX is averaged.
The signal on my last attempt exhibited scintillation you mentioned.  The RX
lens was 6" diameter with a focal length of  8" and a detector size of  5mm
sq.
I know there is a way to figure FOV from those numbers but I cannot remember
it now.

Aiming was not critical, although I was able to "find" the hiding spots my
friend was moving the beam to.
Cloudbounce Hide and go Seek.

So these diodes I just received are +/-   5 degrees to the -3 db point much
tighter and the field intensity at the clouds should many times what I had
with the last array.

With a laser the dot size on the clouds is so small that  say a 1 degree FOV
RX would be seeing mostly noise.
If one figures 1mR divergence at about .06 degrees, hell of a power density
but scintillation, aiming problems etc.

No I never did find a ham or other enthusiast to experiment with around
here.
Wish I could.

Thanks Tim

Paul A. Cianciolo
W1VLF
http://www.rescueelectronics.com/
Our business computer network is  powered exclusively by solar and wind
power.
Converting Photons to Electrons for over 20 years

-----Original Message-----
From: laser-bounces at mailman.qth.net [mailto:laser-bounces at mailman.qth.net]
On Behalf Of Tim Toast
Sent: Friday, July 15, 2011 8:17 AM
To: laser at mailman.qth.net
Subject: Re: [Laser] New Cloud bounce system being built Optical detectors

Hi Paul,

Several in here have had good results when using LED arrays for NLOS. For
lower noise operation of the K3PGP receiver you can try using a lower noise
FET in the front end like a 2SK170 or other exotic fets other than the
regular MPF102. Cooling the detector works good too if you can deal with the
condensation problems.

I think most of the experiments with LED arrays have used receiver fields of
view smaller than the actual transmitter spot on clouds or other objects.
The more of the spot you can fit on the detector the better, i would think -
as long as background noise permits. Aparently, having the entire spot on
the diode will give you much less scintillation than with only part of it.
But that is easier done with a laser no doubt!

Good luck with it! 
- did you find an optical ham on Long Island?

-toast

> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Wed, 13 Jul 2011 11:46:22 -0400
> From: "Paul A. Cianciolo" <paulc at snet.net>
> Subject: [Laser] New Cloud bounce system being built Optical detectors
>     Tim    Toast
> To: "'Tim Toast'" <toasty256 at yahoo.com>, "'Free Space LASER
>     Communications'" <laser at mailman.qth.net>
> Message-ID: <[email protected]>
> Content-Type: text/plain;    charset="iso-8859-1"
> 
> Tim,
> 
> Sorry I missed this response for a while.
> I really appreciate the answer.
> 
> I found a hybrid detector amp in my pile of stuff.
> It has an  area of 5mm2
> The peak response is at 940NM
> Its made by advanced photonics but right now I cannot remember the model.
> Although I do remember that is much quieter than the BB  OPT301 I used 
> during the one way Contact I did about 10 years ago.
> 
> Here is the filter am using  in front of the device. 
> 
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=310313273043&ssPage
> Name=S
> TRK:MEWNX:IT#ht_500wt_922
> 
> Only 8% transmission loss and very sharp skirts
> 
> The last time I did this see here
> http://www.rescueelectronics.com/Optical_Comms.html
> 
> I used 814 940 LEDS I stripped from CATV remotes.  Many Many hours of
work.
> The diodes I used were approx..  25 mw/SR  with 50% beam width  of 50 
> degrees
> 
> These diodes:
> http://www.paralight.us/uploads/pdf/EP2012-350IR1.pdf
> 
> are the one I will be using for this project.
> Each diode is  1 watt/SR in  50% beam width of 10 degrees.
> 
> The  100 diodes will be in any day now.
> The array will have an output power of greater than 100 watts/SR.
> 
> The frequency of choice will be 450 HZ  divided down from 1.8432 Mhz 
> crystal.
> I will investigate this list of detectors Tim.
> 
> But for the moment I wonder if it is possible for some to build a 
> detector amplifier that would have a noise advantage over manufactured 
> hybrid.
> 
> 
> Paul A. Cianciolo
> W1VLF
> http://www.rescueelectronics.com/
> Our business computer network is  powered exclusively by solar and 
> wind power.
> Converting Photons to Electrons for over 20 years
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