[Laser] Lasers vs LEDs & ARRL contests

[Glenn Thomas]

Hi Jon.

My thoughts below...

At 03:59 PM 7/18/2008, W0ZQ at aol.com wrote:
>Hello to all Laser/light enthusiast.
>
>As some of you may  know, I am the ARRL's Dakota Division VHF/UHF Contest
>Committee (VUAC)  representative.  I am seeking your comments.  One 
>of the items
>that  has been under discussion by your VUAC is the ARRL General VHF Contest
>rule 1.12  that states "1.12. 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."  This rule requires that the contact be made 
>by licensed
>amateurs  and that the detection requires at least one stage of 
>electronics, that
>much  seems fairly clear despite whether you agree or disagree with that part
>of the  rule.   What is less clear is the requirement that the source use
>"coherent radiation" and "(for example, laser)".  How coherent is coherent  ?
>
>What I would like your comments on is this.
>
>1.   Given  this rule as it is now, does it include or exclude the use of
>narrow band  LEDs like the Luxor.  I am no optics expert but it 
>seems to me that
>some of  these newer power LEDs are very close in coherence to really poor
>lasers.   Does the current rule have enough latitude to include 
>narrow  band LED
>emitters ?

I don't think that "coherence" is an important attribute. Perhaps the 
best example of this is to point out that the coherent light emitted 
from the "laser pointer" sources doesn't stay coherent for very long, 
losing coherence due to thermal agitation in the lazing material with 
a very few feet of leaving the transmitter.

>2.  IF we could rewrite the rule, what should  the rule say ?  Do we want to
>be much more specific and tighten the rule so  it states "Laser only", or do
>we want to open the rule up to specifically allow  the use of newer
>technologies like power LEDs ?    In either case  what should the rule say ?
>
>It seems that on the one hand we don't want to allow a blinking white light
>bulb, but if not that where is the line ?

I would drop the requirement for coherence, not the least because 
most active hams in this area cannot measure coherence in any case. 
The requirement to have at least one stage of electronic detection 
and that the system be "capable of real communication" is adequate to 
preclude the 'flashlights at 20 paces' scenario. If the light source 
is in fact a flashlight, so what? If the specified detector is used 
and the system is capable of "real communications" (whatever that 
means), why not allow it?

The requirement for an Amateur license also seems superfluous because 
there is (so far) no license required for optical communications. 
Given this, restricting recognition to licensed Amateurs only runs 
against the purpose for the Amateur Radio Service stated in 97.1(b), 
(c) and (d) of the FCC rules.

>Again, your  comments and perspective are most welcomed.
>
>73, Jon
>W0ZQ
>Dakota  VUAC Rep

You're welcome!

73 de Glenn Thomas WB6W