[Laser] Laser comm stuff

[David Rea, K2THZ]

There is one thing that concerns me with all this talk about transmitter
aiming platforms. We know how big our lenses and detectors are at the
receiving end. Though we all have different distance goals, our
transmission distance is a known variable as well.

But without an accurate idea of how wide the beam "spot" will be at the
receiving end, we can't make a reasonable estimate as to how precise our
aiming has to be. Case in point: if you're using a transmitter that will
give you a 300-foot spot at the receiving end of your path, there's no
need to design a transmitting platform capable of 10-foot resolution at
that distance if you don't have any big upgrade plans in store for your
laser.

My proposal: since I don't have any transmitters yet, those of you who
do, take your lasers out to a big parking lot tonight; preferrably one
that isn't lit! Measure the distance from one end to the other and then
measure the spot size of your laser on a piece of copy paper at the
other end of the lot. Theoretically, after a few hundred feet, you
should start to see something larger than a focused point. From my
experience, expect to see spots in the 1-3" diameter range at about
500-1000 yards.

Once spot size and distance are known, we can calculate the divergence
of the laser (probably in microradians). It will be interesting to see
what the average divergence of the variety of pen pointers we have is.
Once we have this, we can all work towards building platforms that are
of appropriate precision...

73
Dave K2THZ

On Fri, 2003-07-18 at 15:18, riese-k3djc@juno.com wrote:
> WOW surprised to see this many folk on the list at this time of day
> 
> Looks like the idea of using threaded rod may be they way to go on the
> cheap
> and looks like everyone including me had/has the same idea. Trig does the
> trick
> as does simple geometry . Angles are the same at 1 Ft as at 30 Miles.
> Micrometers would be the next improvement to allow for smaller increments
> 
> I am not sure what the east coast US distance record is but as I stated
> there are
> several 30 mile paths that I have used on Microwave and are line O sight
> 
> I have a pretty good rcvr working ,,nothing too esoteric but does hear
> bugs etc at night
> as well as the hummmmmm from all the pollution
> 
> one thing
> 
> on several occasions , pointing the rcv to the dark sky I have noticed
> regular ticking sound
> it is directional comes and goes ,, close to the horizon but not on it
> and I have heard it
> from different locations. Usually pretty weak and not aircraft lighting..
> Any theories  ??
> 
>  
> I will crawl back into the wood work for now     HAR
> 
> Bob  K3DJC
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