[NLRS] Use of Light in VHF Contests

[Donn - WA2VOI/0]

Unfortunately, there's a fair amount of ambiguity even in the definition quoted:
-what/which "fixed...  relationship?"
-what/which "phase ?"
-for how LONG a period of time ?

These matter 'cause, for example, lasers have dispersion, or broadening, of 
their spectrum.  How much dispersion are you willing to tolerate before you no 
longer call the light "coherent ?"  That's the problem.  Similarly, how about 
"monchromatic light," i.e., a single "color ?"  No argument that a flashlight 
(or similar) does not qualify... "white" light is ALL COLORS, and therefore 
cannot be coherent.

This is an important question for a couple of reasons (that I can think of, 
anyway):
-some lasers can be dangerous (yes, even the ones that are $10 pointers)
-lasers turn out to NOT be the best way to go for communications.  They produce 
a beam that is too small (in diameter), such that atmospheric disturbances can 
prevent the QSO... think QSB.
-sources such as LUXEON(tm) LED sources are much cheaper, safer, and better 
suited to communications than lasers (many, anyway).  (And no, not all LEDs are 
laser sources.)  Many LEDs produce "monochromatic" light, but with HIGH 
dispersion.   Is it still "coherent ?"  Luxeons produce light that is coherent 
with MUCH LESS dispersion. (Think of signals smeared by aurora vs. non-auroral 
ones.)

The poster, Jon, W0ZQ, did give contact info... 
"http://www.arrl.org/contests/vuac.html".  It turns out he is aVUAC 
representative, and the list gives his snail mail address.  His e-mail address 
is in what you quoted.

73 Donn
WA2VOI/0

----- Original Message ----- 
From: "Ray J" <Ray at w9ray.org>
To: <NLRS at mailman.qth.net>
Sent: Monday, November 30, 2009 10:48 PM
Subject: Re: [NLRS] Use of Light in VHF Contests


>
>
> isnt the Dictionary meaning  pretty foolproof?
>
> coherent light-
> "light in which the electromagnetic waves maintain a fixed and
> predictable phase relationship with each other over a period of time."
>
> lasers should produce a coherent beam of light... a flashlight will not..
>
> w9Ray
>
>
> too bad the arrl vuac representative list doesn't  give any contact info..
>
>
> jcplatt1 at mmm.com wrote:
>>
>> Hello NLRS land.   The ARRL's VHF UHF Advisory Committee (VUAC) has been
>> formally directed to review the adequacy of VHF Contest Rule 1.12 regarding
>> Light contacts.
>> PUBLIC STATEMENT>>>>>>>>>>>>>>
>>
>>
>>    The ARRL VUAC has been directed to review VHF Contest  Rule 1.12 that
>> states "Above 300 GHz, contacts are permitted for contest  credit only
>> between licensed amateurs using coherent radiation on  transmission (for
>> example, laser) and employing at least one stage of  electronic detection
>> on receive"  to determine if the rule should be  modified to make it
>> clearer as to the meaning of coherence.  The VUAC  is interested in your
>> opinion and any suggestions that you may have.   Please forward your
>> comments to your Divisions VUAC representative.   Your Division VUAC
>> representative is listed at  http://www.arrl.org/contests/vuac.html)
>> end >>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>
>>
>>
>> Please provide me, your Dakota Division VUAC representative, with any
>> comments & suggestions that you may have on this subject.   If you are
>> outside of the Dakota Division, I would ask that you send your input to
>> your own VUAC representative - if you have any problems IDing your
>> representative, or cannot contact them for some reason, drop me a note.
>>
>> 73, Jon
>> W0ZQ
>>
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