[Laser] New Cloud bounce system being built Optical detectors

[Tim Toast]

hey Paul,
Here's that FOV formula:
 
F = (57.3/FL) x  D
 
where:
F = field of view size in degrees
FL = focal length of lens or  mirror in millimeters
D = detector or film dimension in  millimeters
 
an example: 
8" focal length  and 5mm2 detector (2.5 x 2.5mm)
57.3 / 203.2mm = 0.28198
0.28198 x  2.5mm = 0.704 degrees FOV
 
in milliradians:
milliradians = degrees x  17.45
0.704 x 17.45 = 12.28 mR FOV
 
A quick search on the Aussie board i saw they had used a 2.2 degree beamwidth 
60 LED array to cover 130 miles NLOS. With strong signal levels using WSJT...
Yves comments on it saying 
- they had enough signal to have used only one LED and still be readable by the 
software. And that the array might be capable of up to 500 miles, which is about 
the same distance lightning pulses can be heard without any processing -
That sounds encouraging...

 
> 
> Message: 1
> Date: Sun, 17 Jul 2011 14:23:20 -0400
> From: "Paul A. Cianciolo" <paulc at snet.net>
> Subject: Re: [Laser] New Cloud bounce system being built Optical
>     detectors
> To: "'Tim Toast'" <toasty256 at yahoo.com>,    
> "'Free Space LASER
>     Communications'" <laser at mailman.qth.net>
> Message-ID: <004601cc44ae$9bea17b0$d3be4710$@snet.net>
> Content-Type: text/plain;    charset="iso-8859-1"
> 
> 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/
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