I believe the ARRL contests require the light source to be coherent.
-----Original Message-----
From: KG4QDZ <kg4qdz@arrl.net>
To: svhfs@contesting.com <svhfs@contesting.com>; NWWSVHF@mailman.qth.net
<NWWSVHF@mailman.qth.net>; Reflector VHF <vhf@w6yx.stanford.edu>;
VHFcontesting@contesting.com <VHFcontesting@contesting.com>
To: <vhfcontesting@contesting.com>
Date: Saturday, March 15, 2003 4:46 PM
Subject: WAS: Ramsey Laser, NOW: Light mode
>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
>receiver
>
>- 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
>hardware
>
>- 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?
>
>73,
>Skip
>
>-----
>Dr. Skip Coppola, KG4QDZ
>EM73ru
>6m, 2m, 70cm: SSB, FM, & Digital modes
>NWS Advanced Spotter
>
>
>
>
>
>
>----- Original Message -----
>From: "Tim Marek" <timm@cccomm.net>
>To: <VHFcontesting@contesting.com>; "Reflector VHF"
<vhf@w6yx.stanford.edu>;
><NWWSVHF@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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