[Laser] 5 mw laser transceiver kit

[Chris L]

I have just one question.

When atmospheric physics dictates that spatial coherence (ie laser light) is a hindrance to scintillation-free communications; when the reliability, ruggedness, safety, cheapness, and measurements taken on the validity of LED-Fresnel combination are proven by a series of world DX records in Australia and America; when ARRL rules have been changed changed to suit those measured results; while lasers are costly devices demanding even more costly collimating optics, and when many governments are imposing bans on the outdoor usage of laser pointer devices...

...why do people persist with lasers for atmospheric optical communication?

Chris Long, VK3AML, 2 Newton Street, Surrey Hills 3127, Victoria. 
Tel: 9890 8164.

http://www.modulatedlight.org

http://www.bluehaze.com.au/modlight/

http://www.cylindersontheweb.angelcities.com

http://www.modulatedlight.org/Dollars_vesus_Decibels_colour.pdf


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> Date: Mon, 20 Sep 2010 06:18:22 -0700
> From: toasty256 at yahoo.com
> To: laser at mailman.qth.net
> Subject: [Laser] 5 mw laser transceiver kit
> 
> Hi All
> 
> It's great to see someone has put a kit together. That is sure to 
> spark some interest in optical coms. In the interest of a little 
> fun competition, it would be nice to have a simple kit for laser 
> com's too. One obvious advantage (or not so obvious) for laser 
> over LED, is size and power consumption. A simple laser transceiver
> could be made very small and portable, even pocket-sized and 
> battery powered. Under 90 ma. for most 5 mw diodes.
> 
> It would help if everyone could start with the same size, easy to
> obtain, enclosure. One that comes to mind is the old "Tuna Tin 2" 
> kits. You could actually use a tuna can (Tuna Tin THZ or 
> Tetrazzini?) but someone suggested to me to use one of those 
> "Altoids" candy tins. They have an easy access door and complete
> sheilding, plus plenty of room for a circuit board and batteries
> inside. These are the large 5" x 3" x 1" inch size boxes. They 
> also come in a couple smaller sizes and even round ones, all with
> resealable metal lids or doors.
> 
> I was looking at some amplifier circuits today and saw this high 
> gain hearing-aid design that uses 3 transistors and one battery 
> (1.5v). If you switch the microphone with a photo detector front 
> end, you have a high-gain receiver plus part of the transmitter 
> too. A laser transceiver could be made very small and energy 
> efficient using a low voltage like 3 volts (2 cells). A 3, 6 or 
> 9 volt design for the small light-weight battery sizes. With a 
> dual 555 timer chip, you can have a simple high quality PWM AM 
> for the laser and a tone generator for MCW or alignment. The 
> goals being low cost, light wieght, easy to put together etc..
> 
> Relatively cheap optics that work well:
> If you are willing to take apart some junk equipment you can find 
> lots of optical goodies. The old VHS Camcorders can supply most of 
> the optical parts. An old DVD player will get you a 5 milliwat red
> laser diode (these are often dual wavelength visible/IR diodes with
> three pins, or four pins if it has a monitor diode) and some small
> lenses to use. These even have one lens you can use to collimate 
> the laser fairly well (the laser pickup "output" lens is a 5mm or 
> 6mm f0.9 or faster type) or it can adapt the beam for use with a 
> larger lens. The main large glass lens on the camcorder is usually 
> a 25 to 50mm f1.0 type when used by itself. It can work for either
> transmitter or receiver. Some of the older ones have a fine 
> adjustment twist focus. 
> For short range use, it might be nice to be able to defocus the
> transmitter and receiver some - up to 10 degrees or more maybe - 
> these twist focusing lenses would be great for that. 
> Inside the camera zoom lens are a few smaller glass lenses in both 
> positive and negative types plus a special "eyepeice" type assembly 
> - similar to a 15 - 20mm Kellner telescope eyepiece. This could 
> make a nice finder when paired with a larger objective lens and a 
> cross-hair. The video viewfinder eyepiece is also adjustable and 
> could be used for either one or a finder. It is usually a 20mm F1 
> or F2 plano convex plastic lens. 
> The performance won't be excellent obviously with these small 
> lenses but should work for the shorter ranges ok. (under 50 miles 
> or so?? :) you can always break out the big optics for better 
> performance.
> 
> 
> tim toast
> 
> 
> 
> 
> 
> 
>       
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