[Laser] Laser comm and ARRL?

[John Matz]

Hi guys,

I have been following this thread for a while, and I'd just like to toss in
my two cents.

First, I'm all for allowing LED contacts too.  It's the electronic detection
that should determine a true communication link.

Laser pens and many other lasers are only a few milliwatts output.  They
have a beam divergence (sometimes made by the transmit optics) of about a
milliradian (0.06 degree beamwidth).  Lasers have 1 to 10 nm of spectral
linewidth.  At 650 nm optical wavelength, that's a Q of about 100.  HeNe gas
lasers are about 1 nm, solid state lasers are about 10 nm, as I recall.

LEDs on the other hand have a linewidth of 50 to 70 nm, for a Q of about 10
... they are a bit wider, not "coherent" by the rules ... but how coherent
is a semiconductor laser ... maybe 5 times narrower?  Just how coherent is
coherent?  Neither is super narrow.  Also LEDs are available that can run IR
and/or have much more output power ... like 1 watt.

For what I've seen, for NLOS contacts to be possible, the approach is an
array of 1 watt LEDs running tens of watts optical power out.  The beamwidth
is wider too, matching the receive beamwidths of 0.5 to 1 degree typical,
making cloudbounce practical.  Note this power is spread over many inches of
source and disperses 10 times faster (safer?).  If LEDs are not allowed, we
must use lasers at 1/1000 the output, and pretty much stick with LOS
contacts and super narrow beams.

A compromise I may try soon is to broaden the TX beamwidth to 10 mr (0.5
degree) to match my RX at 10 mr beamwidth.  The range should be just over a
kilometer then.  With these "broad" beams, I can make contest style contacts
with little difficulty in alignment and just enough range to be legal.
How's that for "complying" with the rules?

John Matz KB9II

----- Original Message -----
From: "Andrew T. Flowers, K0SM" <aflowers@frontiernet.net>
To: <laser@mailman.qth.net>
Sent: Wednesday, February 18, 2004 7:29 PM
Subject: Re: [Laser] Laser comm and ARRL?


> Robert,
>
> The idea that you can just point a laser pen up in the sky and carry on
> a CW qso is pretty ridiculous.  The discussion about NLOS communication
> has mostly involved long-term signal averaging to recover an extrememely
> weak signal.  I don't know of anyone yet who has a mad a QSO over any
> significant distance this way, but it should definately be possible with
> the right equipment and patience.
>
> Cloudbounce echoes can be plenty strong enough to hear.  Still, you have
> aiming issues to deal with since clouds move :-)  I'm playing around
> with the idea of using FSK441 to "ping" the other station rather than
> having the need to stabilize the optics before the QSO.  It works really
> well in the apartment, but I haven't tried it in the field.
>
> Andy K0SM/2 FN13ed
>
> >
> >I'm curious about how the various descriptions of non-line-of-sight laser
> >communications fit into this...  It seems that some folks are saying that
> >you need precise alignment, laser to receiver, etc., whilst others
suggest
> >that they just point the laser and receiver into the same general area of
> >the sky and *voila* - they make a contact.
> >
>
>
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