[Laser] RTTY over light, anyone tried it?

[Paolo Cravero]

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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