[Laser] One way 3 mile laser NLOS contact using PSK31

[Kerry Banke]

James - Thanks for your comments as we're always open to suggestions.    I 
have yet to try broadening the beam to see if that helps or hinders the 
propagation we want.  My gut feel is that keeping it in a reasonably  tight 
beam as far as possible has the advantage of delivering nearly the same 
intensity of scatter along the laser path. I believe going to a more 
diverging beam may not light up the particles as brightly near the receive 
end.  This is just a guess. I do want to try a larger beam expander to keep 
the beam from diverging while at the same time delivering a larger cross 
section of laser beam over the receive location.  I think I need to look at 
the field of view for my receiver at the typical distances to the 
intersected beam to optimize the system.   I have run some simple 
experiments using a red high power LED which has maybe 350 mw optical 
output.  This is collimated with a 4" lens as well but there is no 
comparison as to the scatter signal available off clouds compared to the 
laser system which has much less divergence and only 3 times the power.

I'll certainly keep your protocol in mind as we get farther down the 
road.  It's actually interesting  to note that with  this  approach it is 
easy to find the signal as all you need to do is slowly pan in 
azimuth  above the horizon in the direction of the transmitting station 
until you cross the beam going over head. The beam can  then be 
followed  to search for the strongest signal which may be at the horizon 
for basic dust/moisture scatter or a very narrow  hot spot higher up where 
the beam hits a cloud.

  - Kerry N6IZW -

At 03:19 PM 12/14/2004, TWOSIG at aol.com wrote:
>Good to hear of your success!
>
>
>I had two ideas after reading about your setup.  Don't know if they  are
>worth trying.
>