[Laser] PIN Diode Suggestion

[Bob Williams]

Joel,

You might try the K3PGP frontend with the Photonic Detectors
PDB-V107-ND.  This PIN has a dark current of 1nA and a surface area of
17mm.  The full specs are on the photonic detectors web site.  Digikey
sells those for around $2.00 each.  Watch the surcharge if you don't
make the minimum order.

For reasons that entirely escaped me, I bought the C107 - which is
essentially the same device, optimized for photoconductive mode, rather
than the photovoltaic mode that we are using it in (which is what the
V107 is for)  I was concerned it might not work too well for this
application, since it has a higher dark current.  But having come from
the world of phototransistor frontends, I am astounded at how well even
this does.  

With all the phototransistor receivers I ever built, I had to point at a
light to test the rx.  With this receiver, the K3PGP nighttime front end
feeding just an LM386,  I have yet to find a location in my suburban
neighborhood where the bare detector (no lenses or baffles) does not
pick up 60 or 120 Hz light noise.  Here in the ham shack, the leakage
into the room from around drawn shades at night is enough to detect.  I
also find that I have to turn off the printer, because the AC modulation
on the green power LED is detectable.

I built mine dead-bug style on a piece of PC board and found that the
frontend MUST be shielded, as K3PGP states, to avoid pickup of RF and 60
Hz line noise.  I also find that because I left some leads a bit long,
the thing is VERY prone to microphonics.

I can't recommend this simple, affordable circuit highly enough.  Give
it a try and enjoy.


Bob Williams, AA1ZC
trillium@snet.net
Gales Ferry, CT
Grid FN31XK