[Laser] K3PGP low frequency photodetector with an APD.

[F1AVYopto at aol.com]

Hi all, 
For the first time we have built an optical receiver well  better in 
sensitivity the classic K3PGP RX in the 300 Hz to 2500 Hz  bandwidth.
We use an avalanche photodiode EG&G C30817E in a very simple  schematic.
Compared with a S2386-18K Hamamatsu photodiode (NEP 6,8 x 10^-16  W/Hz^1/2) 
in a K3PGP RX without FET gate resistor, the SNR improvement is over  10 dB at 
300 Hz and well over 20 dB at 2500 Hz ! 
Schematic and curves are at  :
http://pageperso.aol.fr/F1AVYopto/APD/NEWAPDRX2.jpg
http://pageperso.aol.fr/F1AVYopto/APD/PGPAPDresponse2.JPG
This  C30817E APD is a very old one one (1991).
It coms from an old surplus retail  scanner DATACHEKER S.A.B.R. type.
One can buy modern APDs at Edmun Optics but  they are very expensive  !
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2646
The  best SNR is got for a moderate gain and the stability is good.
Yves F1AVY