[Laser] daylight receiver

[TWOSIG at aol.com]

For what it is worth, when I try to access K3PGP's web site, the schematics 
and pictures do not display on my system, just an icon.  If I try to access the 
icon, I get a message that the item is not on the server, or something 
similar.

Having seen the schematic for the daylight version several months ago, and 
from the text, I know that there is an 82K resistor used to bias the photodiode 
from the positive supply.  



Andy, 

Here is something else you might try  --  I seem to remember that your web 
site shows a photo sensor at the end of tube with a 4 inch lens.  Remove the 
photo sensor assembly from the tube with the lens.  Cut out a metal disk (black 
construction paper might work) an put a small diameter hole, maybe 1/16th or 
1/8th inch, in the center.  Then mount the disk in front of the photo sensor two 
to three inches and seal the photo sensor from all light except from the 
small hole.  Re-assemble the sensor into the tube so that the image formed by the 
lens is in focus on the disk.   The field of view will be narrowed to a value 
equal to the diameter of the hole divided by the focal length of the lens and 
the stray light should be mostly eliminated.

This might not be enough to keep the night sensor from saturating, but it is 
worth a try.


James
N5GUI




In a message dated 6/10/2004 9:18:32 AM Central Standard Time, 
wrauscher at gamry.com writes:
Andy,
    On K3PGP's web site is a daylight front end. The basic difference is that
the photo-diode is biased, photoconductive mode rather than photovoltic
mode. There is a sensitivity loss due to higher noise but a much wider
dynamic range.
    I have used the Red covers for LED displays as a filter (look at old
calculators and other stuff that used LED numeric diplays). While not as
effective as a good narrowband filter it does help. If I remember correctly
you can get about a 10dB improvement in SNR.
    I other suggestions are also very good. Look at some telescope building 
web
sites for ideas on reducing stray light in your optical system.

have fun
walt

-----Original Message-----
From: laser-bounces at mailman.qth.net
[mailto:laser-bounces at mailman.qth.net]On Behalf Of Andrew T. Flowers,
K0SM
Sent: Wednesday, June 09, 2004 3:50 PM
To: laser at mailman.qth.net
Subject: [Laser] daylight receiver


Does anyone have a design for a good daylight receiver?  My K3PGP front
end won't hear much in daylight.  I'm not looking for something that is
super sensitive--just good enough for a LOS QSO on a sunny afternoon.  I
was thinking about putting the RX in a black box and using a very small
lens, thus limiting the amount of total light hitting the surface.  I
may also try using a low-value resitor on my OPT310 RX to widenthe BW
and decrease the gain.  Right now it makes a pretty good oscillator if
you hit it with the laser directly :-)

( and yes, I'm too poor to to afford narrowband filters)

Andy K0SM/2

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