[Laser] Re: PSK31 via light - up-convert to RF vs audio amp

[TWOSIG at aol.com]

>From toasty256 at yahoo.com :

>One more thought on this conversion to RF thing.  The
>ultimate in low noise mixing might be using the
>photodiode  itself as the mixer. 
 
 
Hmmm.  Very interesting thoughts.    If the path was  without phase 
distortion ( like a satellite to satellite link ) you could use a  laser for the "Local 
Oscillator" and get lots of bandwidth.  A path in air  would result in so 
much de-coherence that I do not see how you would get  anything but noise.
 
As you suggest, an RF modulated light source might result in a  mixed signal 
that a receiver might handle without adding much internal  noise.
 
A sine wave would probably be less likely to have noise that would  interfere 
with the desired signal.  However, even a asymetric square wave  might also 
serve since the harmonic content of pulsed light would be rejected by  the 
receiver.  Amplitude modulation near the signal frequency would be more  of a 
problem.
 
 
Thank you for you thoughts.
 
James
N5GUI