[NLRS] Use of Light in VHF Contests

[David Palm]

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
>
> ______________________________________________________________
> NLRS mailing list
> Home: http://mailman.qth.net/mailman/listinfo/nlrs
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:NLRS at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>