[Laser] Ramsey Mods

[laser@mailman.qth.net]

I'm back!   Sorry I was out a while.  What I tried to post was rejected by 
the SPAM filters.  First I had to learn that the filters prefer plain text.  
Then, is as usual with the arrogance of my service provider (AOL and its a long 
story), their software won't compose in plain text until I upgrade to the 
latest version which has a lot of things I don't want.  If this works, at least 
they are letting me turn off some of the "fluff" that invites viruses.  (I still 
prefer to use a word processor that will only do text, that way it can't 
execute viruses it wat is supposed to be simple text.)

On the mods for the  Ramsey LBC6:

Andy

We must have different kit versions.  C9 doesn't connect to R2 on my 
schematic.  

Anyway what I think you are doing is taking out the resistor that connects 
the amplifier (U1A) to the LPF.  I would suggest that you leave R2 in the 
circuit because it is part of the filter.  If you lift one end of R2 (the end that  
is common with U1 pin 1) and connect to it, you will disturb the circuit less.

Better yet, cut the trace between Q1 and R1 to isolate the phototransistor.  
It is easier to access and it leave the amplifier in place for you to adjust 
the gain if needed.  R1 can be removed or its value changed if you need diff
erent bias current.  C2 and R3 can be changed to any values needed to match the 
output of the substituted photodetector.  If none of the "stock" components are 
taken off the circuit board, then reversing the mod will be easier if all you 
have to do is bridge the gap where you cut the trace.   

It is too late to work on it tonight, but I will send you the 555 circuits 
that I used.  One is MCW, with the key closure to ground, an LED indicator, and 
adjustable constant current driver.  The other uses similar output driver, but 
uses two 555s to generate simultaneous FM and PWM so it is compatible with 
either type of receiver.

James






Gosh, that was easy. 
Just remove R2--the 100K resistor after the U1A and stick the output of 
the PGP font end into the empty hole that connects with C9.  There you 
go--now you can use your favorite photodiode with this TX/RX combonation 
and gather ALL of the light your lens gives you!  It gives a BIG S/N 
improvement wiht my PDB-V107 (digikey) and "daylight" model front-end, 
but it's hard to quantify just how much on my kitchen table.  Of course, 
you could just complete the RX system by making your own LP filter, but 
this is an easy way to upgrade a piece of equipment you already built.

Next thing to do might be to use the built in test tone for CW mode to 
make a multi-mode transmitter.  It might be just as easy to make a 
simple oscillator out of a 555 timer or something and throw that into 
the line-input....

Andy
K0SM/2


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