[Laser] RTTY over light, anyone tried it?

[Kerry Banke]

We have been using many of the digital modes for our optical communications experiments for quite some years now.  If a computer with sound card is available, it is very easy to set up for using the digital modes and once the hardware is put together, the same setup works for most of the modes available.  The simplest approach that has worked well for us is to amplify the output of the sound card to the point of being able to drive the laser or LED on & off with a square wave.  The receiver audio is input to the computer mic or line input.  Any number of free software programs can be used to transmit/receive over this simple link. PSK31 is very easy to use and works great.  A good programm to experiment with many digital modes is fldigi which can be found at http://www.w1hkj.com/.  I have a schematic of the circuit we use to drive an LED or laser from a sound card and will send it upon request.
73 - Kerry N6IZW
 
--- On Tue, 10/21/08, Zack Widup <w9sz at prairienet.org> wrote:

From: Zack Widup <w9sz at prairienet.org>
Subject: Re: [Laser] RTTY over light, anyone tried it?
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Date: Tuesday, October 21, 2008, 6:52 AM

No but that would be fun!  Run a CQ loop and I'll bet it would be easy to 
tune up/align with!

73, Zack W9SZ

On Tue, 21 Oct 2008, Paolo Cravero wrote:

> Hi.
> I'm slowly coming up with an optical transceiver, with the help of an 
> astronomer for the mechanical part.
>
> So far I have built an MCW transmitter and an OPT202 receiver. The TX is a

> 10mm red LED, and soon the RX will have a nice telescope mount so that
first 
> "beaconed" outdoor tests can take place. No-lens tests took part
indoor on 
> 12m paths, both LOS and NLOS.
>
> But since the astronomer doesn't know Morse code, and is not a
licensed HAM, 
> I am looking for a simpler way to establish two-way communications. A 
> keyboard to keyboard mode would keep the system simple and let non-HAMs
enjoy 
> that part of the spectrum.
>
> The old fashioned RTTY came to my mind (two tones, FSK), so before I start

> building stuff, here I ask: are there any records of optical RTTY 
> communication attempts?
>
> There was a PSK31 discussion few months ago, but in the archives Google 
> didn't find any mention to RTTY/FSK.
>
> I am thinking of the usual XTAL > divider chain with a MUX to generate
the 
> (A)FSK from a serial/parallel port binary output. Or should I better take
the 
> soundcard output, square it (op-amp in comparator mode) and drive the
light 
> source?
>
> Thank in advance for any input/pointer.
> Paolo IK1ZYW
>
>
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