[Laser] One way 3 mile laser NLOS contact using PSK31

[Andrew T. Flowers, K0SM]

Art,
This is pretty much behind the idea of "LaserScatter" (yes, from the 
makers of RainScatter!).  Basically you do very large FFT windows to get 
the frequency resolution required for this kind of work.  I'm not a big 
fan of things like QRSS or DFCW for laser work since we have the ability 
to modulate multiple frequencies, and we don't have the drift problem at 
RF.  They turn out to be relatively inefficient codes in that respect.  
I'll try to work on the code over Christmas break to make it a bit more 
user (and experimenter) friendly.  I have been talking with F1AVY about 
the the what frequencies are best with regard to the PGP receiver and 
various FETs.  Turns out this can be anywhere between 0 and 100 Hz 
depending on things like drain-to-gate impedence (think gigaohms) and 
the capacitance of the diode.  Given the black magic involved I'll try 
to make the code flexible so that you can find your own "sweet spot" for 
your particular setup.

Wouldn't .0001Hz resolution require something on the order of 1 ppm at 
100Hz?  Do you need a TCXO in your soundcard?

Andy K0SM/2  (Three days to vacation.....)

 
KY1K wrote:

> It allows you to set up a complete superhet receiver in software with 
> prefiltering and allows the center frequency to be set (you can look 
> at 350 to 360 hz with up to 256k bins instead of the more typical dc 
> to xx frequency range with the bins divided into that range). You can 
> go down to .0001 Hz bandwidth (or narrower) if needed-just the thing 
> for very weak signals. The display parameters are fully adjustable, 
> and you can change them on the fly instead of stopping the recording 
> and replaying the saved file after making adjustments.