[Laser] laser transceiver

[Tim Toast]

hi all,

Here is a schematic of my laser kit so far (v2)

http://www.angelfire.com/space2/toast/

I'm not really finished with this yet but this is a working demo.
I decided on a shunt modulator for simplicity and laser diode 
safety. Q4 does double duty as audio output and shunt modulator 
depending on the T/R switch S1a-b. A third section of S1 could 
be added to turn laser off during receive.
This kit is meant to use a bare laser diode so the beam diameter 
can be adjusted with an external lens depending on conditions - 
Local or DX. Maybe set it to no narrower than about 5 degrees to 
use it hand-held.
The lens can be adjusted to narrow the beam for DX when mounted 
on some sort of steady mount. A retro-reflector is mounted on 
the front of each transceiver to help alignment. A similar lens 
is used for the receiver. Again for simplicity a photo-transistor 
is used. 
One annoying habit of photo-transistors is that they tend to bias 
themselves completely off in darkness. One way to prevent this 
is to have a small LED source near the photo-transistor to shine 
on it weakly. Only a very small current is required for this, 
about 1 or 2 milliamps, so that it won't turn completely off. 

For daytime use, a narrow filter will be required based on the 
laser wavelength. An adjustable iris may also help keep the 
detector from being saturated in bright daylight.

-toast