[ARC5] Enhancing selectivity in R-26

[Kenneth G. Gordon]

Again, there are two workable methods to accomplish this:

1) Lew McCoy's regenerative 1st IF idea. I have done this one. It is fairly 
easy, but must be installed and used with some awareness of "side effects". 
However, it is effective, resulting in noticeable "single signal" effects.

2) Separate the two coils in each IF can by about 1/4" inch. This method was 
used by A.R.C. just after WWII. I have not yet done this one, but it looks like 
it would be more effective, more stable, easier to USE, and would have 
fewer "side effects".

However, this requires removal and dismantling of each IF can, then 
modifying their interiors. Although the process is not difficult, it is time 
consuming. And it would require far more accurate IF-stage alignment 
afterwards.

Also, the ultimate -60db bandwidth will not be substantially improved since 
this is determined by the IF frequency, rather than by the "Q" of the 
transformers or the coupling coeffecient of the coils.

The -3db bandwidth does become very substantially more narrow, though.

Since the 6 - 9.1 MHz receivers have only one IF coil in each can, there 
would have to be found another method to use here...and, boy, if any of 
these receivers needs enhanced selectivity, these are the ones.

Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John   Wayne