[Laser] led transceiver

[Tim Toast]

That's great Stuart, keep on truckin' :-) 

I don't know for sure if 6.5km is a record, but it sounds like one to 
me.. with potential for much more. I understand that was with a zero 
bias on the LED (-12dB Rx) AND another -12 db attenuator in front of 
the lens! I wouldn't mind seeing some charts and graphs of the 
frequency responces of the different receivers and setups if they are 
out there or can be made. 

A single device type transceiver is looking more and more attractive, 
as long as the receiver is sensitive enough for the ranges wanted. 
I was pondering about a version that uses two of those fine LED's 
which could be used in either a tx/rx diversity mode (simplex) or 
separately in a full duplex mode. I know the digital data people 
would want full duplex no matter how well a PTT system works.

tim toast


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> Message: 1
> Date: Mon, 25 Oct 2010 15:11:03 -0400
> From: stuart.wisher at talktalk.net
> Subject: [Laser] led transceiver
> To: laser at mailman.qth.net
> Message-ID: <8CD428F80864A4F-DAC-2FBB at FRR4-L28./f>
> Content-Type: text/plain; charset="us-ascii"
> 
> 
> Tim,
> 
> 
> 
> You said my 6.5km contact using the led transceiver was a
> record, I was using a 12dB attenuator in line with the lens
> at the time (1" dia hole in cardboard in front of 4" lens
> which attenuates both receive and transmit) which means the
> system is capable of at least 26km. Actually we set out to
> test this last week but the rain came down before I could
> switch over from the Fresnels. All this with zero bias on
> the led. 
> 
> 
> I tested this rig using reverse bias in the lab and the
> gain comes up another 12dB at 33V bias, after that it makes
> a good noise generator. All this gives the rig a potential
> range of 100km.
> 
> 
> I have measured some of the frequency response of several
> heads, The VK7MJ design, K3PGP, and KA7OEI all run up to
> 100kHz using capacitor coupling and a reverse biassed
> SFH2030 diode (only 11pF on spec sheet). Clint's may go
> further but I didn;t check since we usually use about 25kHz
> FM and LSB.
> 
> 
> I am constructing Mk2 LED transceiver at the moment using a
> power led that works as a photo diode, with bias circuit and
> separate power supply (batteries)built in. The current drawn
> is only 0.1 micro amp so the batteries will last for their
> shelf life.
> 
> 
> Stuart G8CYW
> 
>