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

[Kerry Banke]

Andy - I was about to request the frequency flexibility & am glad to see 
you're going to look at that. I much rather be able to work in the 70-100 
Hz range. I currently don't have a pair of field laptops with enough 
horsepower to run LaserScatter well but am working on that.  That's really 
the reason I went with PSK31 for initial tests since I have plenty of 
signal at the three mile mark. We'll soon have two complete sets of laser 
Tx/Rx hardware capable of operating with LaserScatter.
  - Kerry N6IZW -

At 09:08 PM 12/14/2004, Andrew T. Flowers, K0SM wrote:
>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?