[ARC5] Sharpening the RU Receiver with Regeneration

[David Stinson]

With the very kind help of many of our members, I've gotten the 
GF-10 / RU-15 Naval Reserve Command Set up and making contacts.
Still need to dress cables, clean and touch-up some spots
and mount the "Test" meter, but it's getting close:

http://home.netcom.com/~arc5/GFRU.JPG

The RU is a TRF receiver and was intentionally designed to
be broad.   To "tighten it up" for use on the Amateur bands
one can introduce regeneration between the TRF stages.
I've been "noodling" how to do this in a simple, non-destructive way.   
The answer was indeed simple:
Strip a quarter-inch of stiff hook-up and tuck that end
under the grid cap of the second tube from the front.
Run the wire out the top.  Bend the other end back on
itself to make about a three-inch "loop" and poke it 
through the side vent hole nearest the grid cap of 
the fourth tube.  The idea is to use friction between 
the sides of the vent hole and the loop to keep the loop
in place.  Tune to the freq you want, then *carefully*
move the loop in and out until the regeneration is just right.
It is very touchy and will require effort, but you will be 
rewarded with weak signals coming up out of the noise
and sharp tuning.  If it motorboats, pull the loop back a bit.
In fact, you can get the bandpass TOO sharp and distort AM audio.
The audio output level will also have an effect on regeneration.

Here is a short .WMA video file showing what can be 
done if you work at this.  The two QSOs from this morning
were at 3880 and 3890 KCs.  
I did not get the bandpass as tight as I could have.   
You can see the white feedback wire in the background.
With no regeneration, you would hear both QSOs at some level.  
The file is a just under 4 MB:

http://home.netcom.com/~arc5/RURegen.wmv

Use "MANUAL" mode when adjusting regeneration.
As with any regen receiver- if you move far in frequency,
you must re-adjust the regeneration.  However, this is 
offset, at least for me, by the fact that AM activity here
is limited to a few established frequencies.  I don't need 
to change things around often.  I'm not trying to work
the Itchy Armpit, Idaho QSO Party afterall. 

I'm thinking of how to use the vent hole as a mounting point for a
"hank-n-whack free," screw-adjustable feedback plate which 
could be moved back and forth with a knob adjustment.  
This is similar to the idea used in the U.K. TR9D, where 
a phenolic cylinder with a long screw adjustment creates 
a fractional-picoFarad capacitor used for smooth control of regeneration.

More on the project later.

73 DE Dave AB5S