[Laser] Ramsey transmit to CdS

[laser@mailman.qth.net]

Hmmmmm.   I don't quite understand the point you are making.   If I was 
sending a PWM signal at  2.4 GHz and my neighbor HAM is sending another at 2.4005 
GHz, I would expect to be able to separate the two signals.

With the detection scheme used on the Ramsey LBC6, if I am using a red laser 
and my neighbor is using a green one, I cannot tell the difference between the 
two.  For that matter, I cannot tell either from a light beam that uses an 
amplitude modulated current to control the brightness of a neon bulb.

Even if you use LEDs of the same color, the system response the same to one 
that is PWM with pulses at 20 KHz,  at 50 KHz, at 500 KHz.  And if you use the 
same percentage of modulation, you can make it "look" like an LED driven with 
an audio signal with a DC bias current.

I guess that I am really looking for a better detector system.  This works.  
It is (sorta) inexpensive.  And it is what I have.  I would like to know about 
more.

Thank you for your comments.

James
N5GUI


Hi
That is exactly how PWM is used ... classically.  If you truly have a PWM
light source, and the PWM sampling frequency is above 8 khz or so, usually
16 or 20 khz, then the 0-4 khz band contains an exact copy of the sampled
audio source.  The photo detector should have a BW of at least 3-4 khz for
audio.
John Matz KB9II