[ARC5] Easy selectivity increase for receivers.

[Fuqua, Bill L]

If I recall the low frequency receiver IF transformers are constructed differently than the higher frequency  ones.
I'll have to take a look. Reducing the coupling should increase the selectivity somewhat. Perhaps even
putting a shorted copper strap turn between the two coils.
Sounds likes there could be some experimentation here. However, I don't expect a lot of improvement  at MHz 
IF frequencies. I liked the regeneration approach, Q multiplier more or less. Worked well for me
in the 60's. Maybe after Dayton Hamvention and after I get some other projects finished, such as my completely restored1970
hot rod VW Beetle. And my two Berkeley's. Never ending. 
   73
Bill wa4lav

________________________________________
From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf of Kenneth G. Gordon [kgordon2006 at frontier.com]
Sent: Thursday, May 02, 2013 6:35 PM
To: Arc5 at mailman.qth.net
Subject: [ARC5] Easy selectivity increase for receivers.

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

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