[Laser] Simple optical beacon experiment in San Diego

[F1AVYopto at aol.com]

About the PGP RX  response: 
Andy K0SM did a very good work about the effective PGP RX  response.
A typical dark night conditions response curve can be found at:  
http://mail.rochester.edu/~af006m/dark.gif
This noise density curve is nearly  the same that the gain curve.
In fact the RX sensitivity is mostly  determinate by the equivalent value of 
the internal Rshunt PIN photodiode  resistor seen in parallel with the 
amplifier input resistor and the diode  polarisation resistor if there is one.
The best sensitive PIN photodiode we  can find today is the HAMAMATSU 
S2386-18K with a 7. 10-16 W/Hz^1/2Hz NEP.
But  the HAMAMATSU S2386-18K has a typical 20 GOhms Rshunt with a 100 pF 
capacitance  at -1V reverse.
The FET PN4117A that gives good results on the PGP RX  has about the same 
gate leakage resistor value.
A simple 1/2.pi.RC  calculation gives the -3 dB cut off frequency of this 
ultra sensitive PGP RX at  less than 2 Hz! 
However the gain has not the same curve that the S/N at  ULF and with a very 
lowest gain this RX stays very sensitive to 20 Hz but not  much more! 
73 Yves.