[Laser] 5mw laser tranceiver kit

Thu Sep 23 21:57:10 EDT 2010

You may tire of the criticism, ignore the physics, discount the economies. Offering a L-A-S-E-R kit is to push a communications technology in what is clearly proven as a wrong direction, on numerous accounts, is to push experimenters up a fundamentally incorrect path.

Two groups - ours and Clint's - have spent the last decade in proving all of this. Do you really expect us to stand back and say nothing?

So it gripes you. So live with it. The physics, the facts, the economics and the proven results will not go away.

Chris VK3AML.

======================

> From: laser at codeadam.com
> To: laser at mailman.qth.net
> Date: Thu, 23 Sep 2010 20:29:39 -0400
> Subject: Re: [Laser] 5mw laser tranceiver kit
> 
> Is it just me or are others getting tired of the constant bickering over
> lasers vs LEDs?
> 
> I don't recall anyone disputing that LEDs may be far superior for the
> ultimate DX but what does that discussion have to do with putting together a
> "5 mw   L-A-S-E-R   transceiver kit???
> 
> I'm afraid if this continues much longer the "5 mw laser transceiver kit"
> will be doomed before it even gets started!
> 
> I think Chris would met a LOT less resistance if he would post his
> discussion about how much better LEDs are under a different topic other than
> "5 mw laser transceiver kit" as what he is discussing doesn't seem to have
> much to do with this project, which is a "5 mw laser transceiver kit".
> 
> Maybe start another topic, A Portable Briefcase LED Transceiver Kit, or
> something similar, that way those that are really interested in the laser
> kit could at least filter the messages.  Same with those that are more
> interested in the LED system.
> 
> With regard to the topic being discussed, "5 mw laser transceiver kit":
> 
> =====
> > (1) Avoid the coherent (laser) beam option, owing to the high cost of
> > glass diffraction-limited optics necessary for their usage, especially the
> > cost of the large-aperture optics necessary for beam spreading to eye-safe
> > flux densities.
> 
> The 4 for $10 5 mw 650 nm lasers that can be bought over here at the local
> department store already come with optics more than adequate for the "5 mw
> laser transceiver kit".
> 
> =====
> > (2) Avoid the coherent (laser) beam option, owing to beam noise and beam
> > steering effects in atmospheric turbulence.
> 
> Not much of a problem over the distances this project is intended to be
> used.
> 
> =====
> > (3) Avoid the usage of near-IR. A visible beam can be much more easily
> > focussed, collimated and aimed, and when eye exposure occurs, it produces
> > an iris-down reaction in the recipient. To make an IR beam eye-safe, one
> > really has to shift to operating in the middle-IR, above 1.5 micron
> > wavelength. At those wavelengths, the detectors become much more expensive
> > than Si photodiodes, emitters are very expensive and often limited to
> > usage by the military by legislation, the thermal noise in detectors
> > greatly increases over that of detectors designed for visible radiation,
> > and optics assumed to be transparent at visual frequencies can often
> > exhibit opaque behaviour.
> 
> The common variety cheap laser pens that are available over here are around
> 650 nm. not IR.  They are inexpensive, easy to purchase and are legal for
> sale and use in this country.
> 
> =====
> > (3) Use molded plastic optics, not expensive 1/4 wave accurate glass
> > lenses or parabolic mirrors (and especially not coated optics - totally
> > unnecessary). A 10" telescope objective, even a simple parabolised
> > telescope mirror from a Newtonian, can cost upwards of USA$500. A 10"
> > Fresnel lens can be had for about $2, or (as stated by a recent English
> > correspondent to this thread) about 99p.
> 
> Many of us have been using plastic optics with lasers.  They are good enough
> for many projects.  Some of us do use telescopes but only because we already
> have them.  I don't recall anyone suggesting (other than you) that an
> expensive difraction limited telescope was needed to put together a "5 mw
> laser transceiver kit".
> 
> =====
> > (4) Use an optical receiver with an inexpensive P-I-N diode like the
> > BPW34, working into a simple voltage amplifier (NOT a transimpedance amp)
> > of a type designed by Clint - refer sections 7.3, 7.4 and 7.5 of this
> > paper:
> >
> > http://www.modulatedlight.org/Dollars_vesus_Decibels_colour.pdf
> 
> That could probably be incorporated in the "5 mw laser transceiver kit".
> 
> =====
> > (5) If a PhlatLight is too powerful a device for a mass-produced kit,
> > consider the usage of a red LuxeonRebel (around 1 watt input) or even a
> > red Cree high-output LED of more standard design.
> 
> Remember the topic stated "5 mw laser transceiver kit", NOT an LED kit!!!
> The 5 mw laser has the added feature that it runs off a couple of AA
> penlight batteries.
> 
> =====
> > (6) If only night operation is contemplated, the Fresnels and their
> > electronics can be mounted in a simple wooden skeleton framework.
> > Focussing to infinity is all that is required - focussing adjustment is
> > unnecessary, except in initial setup.
> 
> The laser and Rx should fit into something the size of an Altoid tin.  No
> framework required.
> 
> =====
> > (7) Ideally, the tx and rx should be co-aligned (but optically baffled
> > from each other by using an opaque board or cloth between them) in a
> > single unit, to simplify alignment and aiming. Full duplex operation is
> > then provided - and this is a major unrecognised advantage of optical
> > comms.
> 
> Any laser system I ever used was full duplex.  The only light coming out of
> the laser was out the front so no additional shielding was required.  I
> think it was Tim that started all of this and he did suggest mounting the Rx
> and Tx in the same unit.  Many on here have been doing that for years.
> 
> =====
> > (8) The optical unit can be mounted to a 1/4" whitworth T-bolt, to
> > facilitate attachment to a standard photographic tripod (I use a Velbon
> > VGB-3 or a wooden surveyor's tripod).
> 
> Yes, could do that with the Altoid tin also!
> 
> =====
> > These are just suggestions, but as Clint has emphasised, the poor
> > performance of existing optical comms kits and a general misunderstanding
> > of the incompatibility of coherent light with atmospheric turbulence has
> > led to performamnce expectations dismally below current possibilities.
> 
> I don't recall anyone disputing this so what is the problem?
> 
> I think the reason you are meeting such resistance to your ideas is because
> your posts are a bit off topic in relation to the "5 mw laser transceiver
> kit".
> 
> There are many different vehicles on the road.  Just because one vehicle is
> superior to another does that mean we must junk what we are driving and
> purchase the superior vehicle???  Some of us just like playing with lasers
> and will continue to do so as long as they are readily available.  I still
> find what Tim originally posted extremely attractive and would participate
> in the "5 mw laser transceiver kit" project as he originally described it.
> I have no interest in the LED system even if it is the superior system.  I
> would just like to see some progress on the "5 mw laser transceiver kit"
> rather than a heated discussion about LED vs laser.  If that discussion is
> to be continued at least post it under a more appropriate topic and let
> those that are interested in developing the "5 mw laser transceiver kit" try
> to make some progress without constantly being sidetracked by off topic
> posts...
> 
> ===== RESPECT TO ALL =====
> 
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