[Laser] Questions from a newbie

[Andrew T. Flowers, K0SM]

Hello!

I'm looking for some advice on building a TX/RX system for non-LOS 
paths.  I was looking through the K3PGP site and I'm intrigued by the 
possibility of troposcatter in "clear air" and cloudbounce.  I ordered 
parts to put together the  laser "PIN-diode front-end" that's on the 
site.  Is this the most sensitive/lowest NF receiver I can put together 
without spending a fortune, or should I be considering something else? 
 I figure this will be a good start in any event.  I don't really feel 
like messing with PMT's, and battery-power is a must.  Right now I want 
to get the electronics optimized and then I'll worry about the optics. 
 We have several folks in the upstate NY area who are exploring the 
realms of EHF, and this may be another "band" that would be of some 
interest, especially since so many are contesters around here.

Also, any advice on a transmitter design?  I need something that I can 
use on voice and AFSK, since I'm gearing toward using DSP algorithms for 
exceedingly weak signals.  Is there a wayto amplitude-modulate a laser 
in baseband or am I better off using some sort of carrier frequency?  I 
understand that I'll run into QRM from manmade sources in the baseband, 
but I'm also worried about loosing S/N if I use some sort of carrier. 
 Ideas?

Like I said, lots of questions!

Andy, K0SM/2 FN13ed