[Laser] Simple optical beacon experiment in San Diego

[F1AVYopto at aol.com]

Art,
In 2005 I did some experiments with  different modulation frequencies to try 
to find the best S/N with the PGP RX and  with a basic OSD1-5T photodiode 
(sensitive area = 1 mm², R shunt = 1 Gohm, Cd =  20 pF).
I confirm the gain curve is not the same that the S/N curve between  10 to 
100 Hz.
I did test at 10 Hz 20Hz 30Hz....to 350 Hz.
At very low  frequencies when we go from 40 Hz to 10 Hz or lower, the FET 
noise can increase  strongly because the 1/F noise effect (flicker noise)
Most of the sound cards  begin to cut off at less than 15 Hz but the K3PGP RX 
gain seems dramatically to  go up from 100 to 20 Hz and less.
There is a compromise to found for the real  S/N best point and to escape to 
the strong spurious signals at 60 and 120 Hz.  (50 and 100 Hz in Europa).
My best SN results was around 75 Hz.
This  frequency is usable with the FFTDSP programs JASON (I2PHD), WOLF GUI 
(KK7KA /  DL4YHF) and LASERSCATTER (K0SM) 
73 Yves.