[VHFcontesting] WAS: Ramsey Laser, NOW: Light mode

KG4QDZ kg4qdz at arrl.net
Sat Mar 15 19:31:25 EST 2003

This ad brings up an interesting topic I was discussing with my son the
other day. The only light mode requirement is that the light be modulated
and demodulated (at least for contests). Most attempts like this one
digitize audio, or modulate a sub-carrier. It's also my understanding that
distance is limited to a mile or so on a good day, and that aiming and
alignment takes a good bit of time. Sounds crude IMHO. I'll outline my idea
below and you guys tell me if it's something worth trying (but please read
to the end):

The idea is to digitally modulate a broad spectrum high power light source
in more of the way of CW, PSK31, or WSJT type methods with a PC. This means
turning a bright (million cp spotlight, readily available and cheap)
spotlight on and off, essentially (keep reading, that's not all). The
receive end would have a PC with a low-light video cam attached, aimed in
_approximate_ direction. This flashing light would be visible for several
miles at night at least, with some vendor estimates much higher. It would
show up on the cam as a flashing 'dot', size dependent on resolution,
lenses, etc. Software would be written that would allow the receiver
(person) to drag a selection area over the spot visible on the screen, which
would then direct the software to demodulate (decode) the brightness change
in that region. Thus, transmit and receive using modulated light, but with a
'higher level' of technology as is done in the tougher methods like EME,
HSMS, etc. The synopsis is:

- It is really mod and demod communications as is other digital modes (it
should be contest legal)

- The software can allow the receiver to select multiple regions on screen
for roundtable type QSOs (not possible with current lasers)

- Repeating is easily done

- Night time is equivalent to a "band openning" on other bands - HF has
day/night propagation changes too, or view daylight as QRM (and it can still
be usable with less range)

- The lenses do what the yagi directors do, literally

- The transmitting antenna is purely resistive (I couldn't resist ;)

- The visual display on the PC through the cam of the horizon is equivalent
to a band DSP type display or waterfall display

- The equipment is cheap, easy to understand, and available

- The challenge would be speed, with simple on/off of the beam being slowest
but usable

- Rovers or even bases could look out on the horizon and see if there were
stations transmitting (easy to pick a QSO and aim)

- Aiming is non-critical for the transmitter and very non-critical for the

- Think of the beacon possibilities! (it would be possible to use multiple
beams and receivers to be omnidirectional much like phased dipoles on a
repeater tower)

- The cam can be tower/rotator mounted and aimed, and would benefit from
height too

- The 'standard' would be in the software, not the hardware, for modulation,
and easily upgraded or added to, rather than using incompatible laser

- There are no FCC spectral purity requirements on light as far as I know ;)

- It should even be possible to write code that would 'auto-acquire' signals
off the cam, but it would be a more complex program

Anyway, that's it in a nutshell. While I think even a crude system such as
this will work with basic parts, there's also room for improvement in the
beam on/off rate, beam focus, and receiver sensitivity and selectivity
(lenses, software, CCD). So, there's something to tinker with too! The
encoding could be adaptable to a variable rate for compatibility to folks
improving their transmitters, and it could include error-correction as some
of the other digital modes do.

I'm not a digital mode guru, but am still pretty new and was just doing some
zero-based-thinking (solve the problem from scratch without the accepted
baggage). The only downside (besides being still line of sight) I see is
that usually the information rate increases with carrier frequency, and this
takes a step backward in information speed, but, so does HSMS and EME and
the other MS modes, so it shouldn't matter. Right?

It also could be too difficult to pick up enough light off the flashing
signal in the video cam, but I also do astrovideophotography, and we pick up
some VERY low light objects millions of miles away successfully, so it looks
very do-able. The telescope helps ;) and might even be usable for this (a
Newtonian telescope employs a parabolic reflector to focus the light to the
eye (the receiving surface). Sound familiar?

OK, let the arrows fly! <G>  Or, does anyone want to help write some s/w?


Dr. Skip Coppola, KG4QDZ
6m, 2m, 70cm: SSB, FM, & Digital modes
NWS Advanced Spotter

----- Original Message -----
From: "Tim Marek" <timm at cccomm.net>
To: <VHFcontesting at contesting.com>; "Reflector VHF" <vhf at w6yx.stanford.edu>;
<NWWSVHF at mailman.qth.net>
Sent: Saturday, March 15, 2003 11:19 AM
Subject: Ramsey Laser Communications Unit

> Check out the New Laser Comm Unit from Ramsey Electronics!
> Tim - K7XC - DM09ol... sk
>  http://k7xc.tripod.com/ramseylaser/

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