[Laser] 5mw laser tranceiver kit

Mon Sep 27 12:35:51 EDT 2010

On 2010-09-27 12:00 PM, laser-request at mailman.qth.net wrote:

> Message: 1
> Date: Mon, 27 Sep 2010 00:08:00 -0500
> From: "Mike"<mikecouture at bellsouth.net>
> Subject: Re: [Laser] 5mw laser tranceiver kit
> To: "'Free Space LASER Communications'"<laser at mailman.qth.net>
> Message-ID:<98289.42697.qm at smtp101.sbc.mail.mud.yahoo.com>
> Content-Type: text/plain;	charset="US-ASCII"
>
> To All,
>
> Here is an example of a very powerful LED, 850nm, etc.. Ebay has several,
> here's an example: 330357511250. I'm not sure if this is the way to go when
> you try to focus it, but hey, that's why we expermint.

Hmm, is that a single LED, or an array?  It's hard to tell from the 
photograph, but it
does look like one LED, although I'm not sure of the manufacturer. 
You'd obviously
want to get rid of that diffuser, though.  Plus, it sounds a little 
pricey.  Do any of the
big LED makers offer high power infrared LEDs?

For that matter, would you really want to go infrared?  You have to be a 
little careful
with optics for infrared, since the properties may be a bit different 
than for visible.
Plus, infrared requires some equipment to assist with the aligning 
(e.g., cheap digital
camera that can see into the infrared).

This prompts an interesting question.  Has any one seen any of the 
edison based
LED light bulbs in any colours except white?  I wonder if it would be 
possible to modify
one of these as an optical source (Yes, I know about electric line 
safety issues and
such.).  Might be something to think about.

> ------------------------------
>
> Message: 2
> Date: Mon, 27 Sep 2010 2:24:12 -0400
> From:<n5gui at cox.net>
> Subject: Re: [Laser] 5mw laser tranceiver kit
> To: Free Space LASER Communications<laser at mailman.qth.net>
> Cc: Tom Becker<GTBecker at RighTime.com>
> Message-ID:<20100927022412.MPP0W.983943.imail at eastrmwml48>
> Content-Type: text/plain; charset=utf-8
>
> Tim and Tom
>
> An interesting schematic.
>
> What I see is the need for the microphone and the photodiode to be "matched" in their characteristics.  Otherwise one, and I presume it would be the photodiode, will not have enough system gain.  I suppose that it might be of practical use if you load down the microphone element so that at the amount of gain needed by the photodiode, it does not overdrive the amp.

Yes, I was wondering about that.  An impedance and/or level mismatch 
could adversely
affect the operation.  As cheap as transistors are now (even cheaper 
than switches!), it
may be better to just duplicate the circuit.

> Likewise on the output, the LED and the 8 ohm earphone ( or speaker, or other load ) would need to match.
>
> If the thought is to drop in a LASER, the problem on output becomes even tougher.  LEDs are pretty linear current to light conversion devices, but LASERs are not.
>
> That is not to say that I see anything that is fundamentally wrong with the circuit.  A commercial device might well be simplified to that point minimized part count or otherwise optimize the design.
>
> I think that if I tried to design a practical prototype using that schematic, I would probably go nuts trying to balance both inputs and outputs.  Not that I would have far to travel, or much skill at the task.
>
> James
>   n5gui
>
> ------------------------------
>
> Message: 3
> Date: Mon, 27 Sep 2010 08:07:24 -0400
> From: Tom Becker<GTBecker at RighTime.com>
> Subject: Re: [Laser] 5mw laser transceiver kit
> To: Free Space LASER Communications<laser at mailman.qth.net>
> Message-ID:<4CA088FC.5020403 at RighTime.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
>    Pondering, I wonder if half-duplex - despite the simplicity - is a
> good idea.  Due to the narrow beamwidth, alignment is critical so
> instant pointing feedback would be very handy. In half-duplex, I can
> envision Johnny and Billy saying "Can you hear me now?" until they give
> up and head for the Wii, but hearing the hiss of the other end in
> full-duplex might help avoid that frustration.

Ah, an interesting idea.  How hard would it be to build an interface for 
a Wii to
allow digital data transmission over an optical beam?  ;-)

> Tom
> http://www.ustream.tv/channel/bowcam
> http://www.ustream.tv/channel/cape-coral-marine-radio VHF
> http://67.207.143.181/vlf9.m3u VLF
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Mon, 27 Sep 2010 17:39:45 +0300
> From: "Zilvinas, AUGMA"<zilvinas at augma.lt>
> Subject: Re: [Laser] 5mw laser transceiver kit
> To: Free Space LASER Communications<laser at mailman.qth.net>
> Message-ID:<4CA0ACB1.8060807 at augma.lt>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Wouldn't be simpler/cheaper to use bike reflectors attached right on the
> correspondent's receiver ?

Retro reflectors are, generally, a good aiming device (and, cheap plastic
bike reflectors are mostly adequate; mostly).  However, while these work
well at night, ambient light tends to swamp them in the day.

> Just my 2c from Zilvinas, LY2SS
>
> ------------------------------
>
> Message: 5
> Date: Mon, 27 Sep 2010 11:24:59 -0400
> From: Tom Becker<GTBecker at RighTime.com>
> Subject: Re: [Laser] 5mw laser transceiver kit
> To: Free Space LASER Communications<laser at mailman.qth.net>
> Message-ID:<4CA0B74B.6020006 at RighTime.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>    >  ...  use bike reflectors attached right on the correspondent's
> receiver...
>
> A good idea in reduced light but, I can tell you from much experience
> pointing at reflectors in daylight, it isn't easy at any appreciable
> distance.  One tends to look down the barrel of the pointer assuming
> that's where the beam is - and usually isn't.

It can, of course, be useful to mount a targeting scope (e.g., rifle scope)
on to the transmitter and receiver.  This can give you a good starting 
orientation
for alignment.  And, you can get some pretty cheap scopes, although this 
may
push the price of a kit above what is desired.

> This raises another issue.  A sunblind detector, one that does not
> easily saturate in daylight, requires a little more thought.  Under what
> reasonable conditions should this communicator operate?

Good question.  Night time is easy.  Day time requires narrow band optical
filters, AC coupled amplifiers, and, possibly, a subcarrier.

> Tom
> http://www.ustream.tv/channel/bowcam
> http://www.ustream.tv/channel/cape-coral-marine-radio  VHF
> http://67.207.143.181/vlf9.m3u  VLF

Dave