[Laser] Coherent Source - back on my soap box

[C. Turner]

To contribute to the muddle, I might weigh in here, as I've been 
somewhat involved in non-laser 2-way voice communications, in addition 
to laser comms.

I would agree that the original intent of the "coherent" statement in 
the rules was to discourage "flashlight" communications and encourage 
all-electronic means of making the contact.

At the time the rule was written, though, it would seem as though those 
writing it didn't envision many means of generating "coherent" light 
other than a laser and the use of such a statement was, perhaps, a bit 
short-sighted - but the fact that they didn't specifically require a 
laser also implied that they were leaving an "out" for some unforeseen 
(pun intended) future technology.

In my opinion, the point is somewhat moot these days.  While one could 
argue (successfully) that even the most coherent light beam rapidly 
loses coherence after traveling through the atmosphere even over a short 
distance, the real proof in the way the rule is, in fact, interpreted 
these days is in two pieces of paper that I have in my possession:  For 
both 2007 and 2008, I took 1st place in the ARRL 10 gig and up contest 
for the 7th call area.  For 2007, this was for exactly one QSO:  A 172km 
2-way voice QSO conducted using LEDs.

That effort is documented here:  
http://modulatedlight.org/optical_comms/optical_qso_107mile.html

For 2008, mother nature relented a bit and 10 gig SSB was added to the 
mix, but points were also gathered from another 2-way optical QSO, again 
using LEDs.  Just for the heck of it, we (K7RJ and I) successfully 
conducted another QSO over the same (172km) optical path using cheap, 
red laser pointers:  Although the results weren't as good as with the 
LEDs for a number of reasons, it still worked.  (Is this the 
longest-distance 2-way voice laser QSO on record?  'dunno...)

That effort is documented here:  
http://modulatedlight.org/optical_comms/contest_2008.html

Oh, and we also did a longer-distance than the above - see the web page 
for details.

73,

Clint
KA7OEI