[Hallicrafters] SX-25 coil loops etc

[Troglodite at aol.com]

In a message dated 8/3/05 2:05:01 PM Central Daylight Time,  
k9tr at dtnspeed.net writes:

>adding a movable shorted turn is an interesting and
>fairly easy  to accomplish method of reducing inductance.   It also
>reduces  Q but not significantly as the shorted turn isn't in series with
>the  actual inductor.
 
Years ago, one of my jobs was aligning AM/FM tuners as they came off the  end 
of the line. For setting the tracking, I used two sizes of "diddle sticks."  
These are a plastic piece with an inductance increasing element on one end, 
and  an inductance decreasing element on the other end. For AM, it was powdered 
iron  and aluminum, and for FM it was ferrite and brass. Bringing each end 
close to  the coil you were trying to align would tell you which way it needed to 
 go.
 
The Radio Amateurs Handbooks from the prewar years (1938-1941) had a  2-1/2 
meter VHF receiver design that used a shorted turn for tuning. Actually,  the 
oscillator inductance was mounted at a 45 degree angle, and a plastic shaft  
carrying a brass washer also mounted at a 45 degree angle was in close  
proximity. 180 degree rotation of the shaft resulted in the washer being either  
parallel to, or at right angles to the inductor. I always thought it was a  clever 
design. Who remembers that rush of a superregen?
 
Doug Moore