[Laser] PIN photodiodes....

Thu, 21 Aug 2003 17:38:40 -0400

Bob,

The silicon-based photodetectors have a spectral peak right around 
900nm. You are right about the PDV-V407--I am using the PDB-V107, which 
doesn't block IR.  You can find some that have extended sensitivity into 
the blue/violet range, but that's not something we really care about nor 
desire--it just means there's more junk that could get into the 
detector.  Some PD's have an IR filter on it to cut out visible 
light--this might be an advantage for you if you have interference 
problems from manmade sources.  You'll want to be careful about which 
wavelengths you choose--there are a few wavelengths in near IR that have 
high absorbtion due to elements in the atmosphere--Oxygen and Nitrogen 
mostly.  I'm not sure what they are right off hand, but I'm sure someone 
on the list knows (hint hint).   Also be aware that Sodium lamps have a 
big peak right around 850nm--you get alot of that scattering off of the 
sky from city lights.  All of this will sound like 120Hz buzz in the 
audio passband, though only the first few harmonics of 120Hz are of 
significant strength--at least from the lights I see in the downtown 
Rochester area.

The program I use for the audio analysis is called CoolEdit Pro 
(www.syntrillium.com), but it's a hefty piece of software.  I'm a music 
grad-student in real life, so I have all of these cool toys.  Depending 
upon what you want to do, there is various open-source software that can 
do audio analysis.  Check out http://audacity.sourceforge.net , as it is 
one of my favorites--runs on all platforms too!

Make sure you build a pair of the recievers--it's much easier to get 
folks involved you give them one to try out.  This works well with 
microwave gear too, but it's much cheaper to build a loaner rig for 
470THz than it is for 24 GHz!  

Make sure you shield that RX, or else you *will* hear your local radio 
stations.  What are you using for the transmitter?

Andy
K0SM/2

Confrey, Bob wrote:

>Andy,
>   Thanks for the info.  I had heard that the CLD-142 would work, just hard
>to find.  I looked at the PDV-V417 from Digi-Key but noticed that it's
>spectral peak was more towards the visible (green) I think.  I was planning
>on using 880nm diodes to do some cloud bounce experiments.  I have seen some
>T-3/4 package PIN's on DK's page but was not sure how well you could focus
>on the rounded diode top?  I would prefer a flat windowed device.  Your web
>page has provided some useful info, what is the Spectrogram program you have
>displayed on your page?  There is very little (none except me?) activity on
>VHF/UHF and
>Microwave down here in GA, EM83DN.  So cloud bounce expermints may be my
>only way to hear any sigs!  Thanks again for the
>info.....73...Bob...WA1EDJ/4...
>
>-----Original Message-----
>From: Andrew T. Flowers, K0SM [mailto:[email protected]] 
>Sent: Wednesday, August 20, 2003 5:15 PM
>To: [email protected]
>Subject: Re: [Laser] PIN photodiodes....
>
>
>Bob,
>
>I've used two different diodes with the PGP front end.  One is the 
>Clairex CLD-142 and the other is the PDV-V417-ND from Digikey:
>http://www.digikey.com/scripts/us/dksus.dll?Detail?Ref=94910&Row=232509
>
>The the CLD-142 is discontinued, but I think Moxley Electronics still 
>has a few.  It looks like a TO-99 transistor with a plastic lens in the 
>top.  It has a a much smaller detector area and is thus a lower noise 
>device.  The digikey part has a larger detector, which gives you a 
>larger target with your lens--if you are thinking of using a fresnel, 
>this is the way to go without breaking the bank.  Besides, I can attest 
>that weak signals will *not* be a problem on LOS pathsuntil you get into 
>the tens of miles.  I'm sure other folks know much more about what is 
>out there in the photodiode world, but at $5/ea it's not too bad.   Just 
>make sure you order enough other stuff to avoid the $5 handling charge 
>(I think $25 min).  That's usually not a problem for us hams.  The 
>panasonic device you mention has less than 1 mm^2 of active area--you 
>have to be right on with your lens--any light that doesn't hit it gets 
>wasted.  You can do this with a good glass lens, but forget it with a 
>fresnel.  The bigger the lense is the more gain you have, just like the 
>dish..and like a dish and energy that doesn't hit the detector is lost.
>
>FWIW, I can hear stuff I can't see with my PGP RX and a 4" lens.  We're 
>looking at non-LOS stuff once we get some good aiming systems worked out 
>(clouds, microwave radomes, etc).  There is alot of microwave activity 
>up here in the Rochester area, and laser comm stuff fits in with all of 
>the contesting and even weekend activity that goes on around here.  I 
>have some stuff on my site that might give you some ideas, if you 
>haven't looked at it yet:
>
>http://mail.rochester.edu/~af006m/index.html
>
>Andy
>K0SM/2 FN13ed
>
>Confrey, Bob wrote:
>
>>    Where can I find a good PIN diode for the K3PGP front end?   I've
>>looked at Digi-Key and found some (few) like a Panasonic PNZ331F.  Is it
>>
>any
>
>>good for
>>The PGP frontend?   My intended use is troposcatter, night, weak signal.
>>Thanks!...Bob   WA1EDJ..... 
>>
>>
>>    - - - - - - -  Appended by Scientific-Atlanta, Inc.  - - - - - - -  
>>This e-mail and any attachments may contain information which is
>>
>confidential, proprietary, privileged or otherwise protected by law. The
>information is solely intended for the named addressee (or a person
>responsible for delivering it to the addressee). If you are not the intended
>recipient of this message, you are not authorized to read, print, retain,
>copy or disseminate this message or any part of it. If you have received
>this e-mail in error, please notify the sender immediately by return e-mail
>and delete it from your computer.
>
>>
>>
>>--- StripMime Report -- processed MIME parts ---
>>multipart/alternative
>> text/plain (text body -- kept)
>> text/html
>>The reason this message is shown is because the post was in HTML
>>or had an attachment.  Attachments are not allowed.  To learn how
>>to post in Plain-Text go to: http://www.expita.com/nomime.html  ---
>>_______________________________________________
>>Laser mailing list
>>[email protected]
>>http://mailman.qth.net/mailman/listinfo/laser
>>
>
>
>
>_______________________________________________
>Laser mailing list
>[email protected]
>http://mailman.qth.net/mailman/listinfo/laser
>
>
>--- StripMime Report -- processed MIME parts ---
>multipart/alternative
>  text/plain (text body -- kept)
>  text/html
>The reason this message is shown is because the post was in HTML
>or had an attachment.  Attachments are not allowed.  To learn how
>to post in Plain-Text go to: http://www.expita.com/nomime.html  ---
>_______________________________________________
>Laser mailing list
>[email protected]
>http://mailman.qth.net/mailman/listinfo/laser
>