[ARC5] Easy selectivity increase for receivers.

[Kenneth G. Gordon]

I had run across the following method recently myself, then was told by Ray 
Osterwald of Electric Radio that Norm Chipps N3RZU had published the 
same info back in the June 1999 issue of ER magazine beginning on page 
29.

"Operating" on the IF cans of the 3-6 MHz and 6-9.1 MHz receivers, 
following the same method used to vary the selectivity in the LF receivers,  
results in greatly increased selectivity, and no apparent loss in gain.

Remove IF cans' covers, remove the long screw down the center, and 
replace the shorter ceramic spacer in the center with the longer one that is 
on the bottom, then put the shorter one at the bottom, and replace the screw.

Be careful of the wires that connect the coils to the connections: those may 
have to be heated up until the solder melts then "slid" down the connection 
wires to get the coils further apart.

This reduces the bandwidth by 50%. In one case, this operation reduced the 
bandwidth from 15 Khz to 7 KHz, although the author did not make it clear to 
which receiver he was referring.

Going further and moving ALL the ceramic spacers to the center, between 
the coils, reduces the bandwidth even further, but does reduce the overall IF 
gain a bit.

Bandwidth in several cases was reduced to 4 KHz, but the author doesn't 
make it clear which receiver he is talking about here either.

Apparently, according to the article, ARC did just this sort of thing with many 
of the receivers they bought back from the gummint after WWII, then sold.

Kenneth G. Gordon W7EKB

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