[NLRS] Use of Light in VHF Contests

[Clare Jarvis]

I suspect that coherent was required to keep us from bringing out flashlights, searchlights etc and decoding using the eye. or just 
using iluminated signs.


So we value human decoding if the signal is demodulated using electronics but we do not value human decoding  if  no demodulation is 
necessary.

de K0ny     Clare




On Tuesday 01 December 2009 08:58:15 David Palm wrote:
> Those were some very interesting comments, Jon.  One question I have: what
> is the rationale for specifying a "coherent" light source at all?  We
> certainly don't specify that our radio sources must be coherent--far from
> it.  So why should there be some difference as we get to this high end of
> the spectrum?  Does anybody know what lies behind including this specific
> term and any good reason why it should be retained?
>
> 73,.
>
> David  W9HQ
>
> On Tue, Dec 1, 2009 at 8:52 AM, <jcplatt1 at mmm.com> wrote:
> > I am taking my VUAC hat off for a discussion.   Before I dive in, I would
> > like to point out that I am not a physicist, nor do I play one on TV.
> >
> > Coherence is not a yes/no parameter, it is not an attribute - there are
> > degrees of coherence.   There are also different kinds of coherence (or,
> > different ways to measure coherence).  To have a contest rule that simply
> > states "using coherent radiation" is not enough information.  Remember
> > that this rule was most likely created some time ago when Lasers were
> > novel and solid state light emitting devices was emerging technology.  
> > The current rule also does not state that one has to use a laser, it says
> > ""using coherent radiation, e.g. Laser", so it points to a laser as one
> > example of coherent radiation.
> >
> > In my brief review of the current state of the art in light emitting
> > technology, in attempting to understand (?) and to identify degrees of
> > coherence with different types devices, it becomes a specmanship game -
> > that is, how do you define the measurement of coherence, and then give
> > that, where is the line as to "this is coherent, but this is not".
> >
> > Compounding this discussion is the real world.  Darn that real world.
> > There are three points.   First point is that highly coherence light,
> > like a laser, is actually not a very good choice for long distance
> > communications through the atmosphere.  Some of the better laser DX
> > records actually place a diffuser in front of the laser to decrease its
> > coherence. Second, lasers carry safety issues.  As amateur radio op's, we
> > know that the way to make longer haul contacts is with more power -
> > aiming a high power laser carries all sorts of negative issues !   
> > Third, low cost, high efficient, high power, monochromatic LED light
> > sources have become available and are now one of the top technologies of
> > choice for long haul Light communications (and they are much safer to use
> > than a laser).
> >
> > So we circle back to the question.  What should rule 1.12 say ?   I have
> > heard general agreement that the part of the rule that requires at least
> > one stage of electronic detection is good - that should stay.   But what
> > about the part of the rule regarding the signal source - should the rule
> > be stiffened to say "only laser", should it be modified with a statement
> > as to how coherence is measured and what the spec is (ex: 1 cm, or 1 mm),
> > should the rule be tailored towards a requirement for being monochromatic
> > and allowing the use of both laser and LEDs ?   Or, should it say
> > something else.
> >
> > One thing that I am sure of.  There is a lot of interesting work going on
> > with Light communications.  I think it would benefit both that work & its
> > technology, as well as contesting in general, if the rule would be
> > inclusive and would encourage continued development rather than be
> > divisive and stifling.
> >
> > Please keep your thought and ideas coming.  What are your thoughts as to
> > what rule 1.12 should say ?
> >
> > 73, Jon
> > W0ZQ
> >
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-- 
Mr. Clare Jarvis
President, Jarvis Computer Software
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