[amsat-bb] Re: RX only satellite?

[G0MRF@aol.com]

Weird idea number 2.
 
You mention "no transmitters"
But thinking out of the box a little....If you carried forward your idea of  
the Laser beacons from your earlier project, then it may be possible to  
"transmit" something after all. -
 
How about one of the new Hi power LEDs?   5 Watts to 20W are  available now. 
Just run it at whatever power suits the power budget.
 
Have the onbard RX activate the LED for a limited period on receipt of a  
command.
Two simple methods of data transfer come to mind.
1)  Switch the LED on and off at an audio rate with a 1:1 square wave.  Then 
turn that signal on and off with a CW generated message. Simple but  
effective. We know that works over 150 miles from recent reports from Australia.  
Receive using software from weaksignals.com
 
2) Much nicer. - Switch the LED on / off at some spot frequency between 12  - 
20kHz.  But arrange for the waveform to be pulse width modulated. Easy  !  
One comparator and a rectangular wave at 20kHz. - Audio on the other  input.  
You can send anything generated at audio including PSK31 speech,  JT65, Domino, 
etc.
 
I imagine the sat will be attached to the ISS.  Tracking is easy too.  Pick a 
night or early morning when a visible pass will occur.  Track the  ISS while 
it is in sunlight then when it reaches the terminator, activate the  LED 
transmitter. Your tracking should be spot on and the signal can be received  with 
very modest equipment.
 
The receiver on the ground is a magnifying glass lens about 4 - 6inches  
across. - Or a small telescope. A BPW34 Pin photodiode followed by a low pass  
filter to remove the 20kHz.  What comes out is audio. - That can be fed to  a 
computer soundcard.
 
73
 
David