[Laser] Re: Laser Digest, Vol 2, Issue 5

[Jim Moss]

http://www.intor.com/

I bought some 10nM filters from these guys a couple years ago.
Good prices and lots of stock values.
Just need a filter big enough to cover your detector, not your lens...

Jim
N9JIM

--- wa4qal at ix.netcom.com wrote:
> One of the problems with most designs is that the dynamic 
> range is so small in the optical receiver front end that ambient
> daylight saturates the front end.  And, once the front end has
> been saturated, it doesn't matter how much more signal power
> you pump into it, you won't get any signal out.  
> 
> Obviously, the first thing to do is to design the optical part of the
> system to exclude as much ambient light as possible.  This usually
> means long light shades (e.g., PVC pipe spray painted black inside
> to limit the acceptance angle of incoming radiation, and to minimize
> reflections).  Additionally, it may mean focusing devices to further
> limit the acceptance angle, and to increase the signal power to 
> ambient illumination.
> 
> Spectral filters can help, too.  Note that spectral filters don't have to
> be exceedingly expensive.  Sure, the custom designed ones with 
> 100 Angstrom bandwidths are worth their weight in gold (or more!).
> But, something as simple as a theater lamp gel can attenuate some
> ambient light without reducing the signal light excessively.  And, they're
> pretty cheap, too.
> 
> After you've done all you can to minimize the ambient light in the 
> signal path, then it's time to start working on the electronics.  One
> approach that I've used is to transformer couple the optical detector
> (PIN photodiode) to the high gain, high impedance front end (JFET IC).
> The transformer coupling removes the DC component of the signal
> while still allowing any AC component through.  It may not be perfect,
> but I've used it to communicate across a well lighted (fluorescent) 
> conference room.  Anyway, it's another design to think about.
> 
> Dave
> WA4QAL
> 
> -----Original Message-----
> 
> Date: Wed, 09 Jun 2004 16:49:57 -0400
> From: "Andrew T. Flowers, K0SM" <aflowers at frontiernet.net>
> Subject: [Laser] daylight receiver
> To: laser at mailman.qth.net
> Message-ID: <40C777F5.5080802 at frontiernet.net>
> Content-Type: text/plain; charset=us-ascii; format=flowed
> 
> 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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