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@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@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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