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

Clair J Robinson k0cj at juno.com
Sat Mar 15 19:02:40 EST 2003

It sounds good. The SW shouldn't be a problem. Just a matter of doing it.
But what do you have in mind for a light source and how do you propose to
modulate it?

73, CJ K0CJ

On Sat, 15 Mar 2003 19:31:25 -0500 "KG4QDZ" <kg4qdz at arrl.net> writes:
> 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 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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