Hello All,
After several requests to develop an alignment system for the popular,
compact Sony ICF-SW7600GR portable, I finally decided to dig in to the
circuitry, and investigate the stock loopstick thoroughly. Perhaps the
fact that
an upcoming family vacation (during which our compact vehicle would not
accommodate the 30" or 19" loopstick modified ICF-2010's) had something
to do with
my motivation.
The SW7600GR loopstick is in fact a smaller version of that used in
the
ICF-2010, i.e. a large, fixed center coil and a much smaller end coil,
used
(in Sony's design) for adjusting the spurious signal rejection of the
loopstick. Like the ICF-2010 system, there is no way to align the fixed
coils on
this antenna. The only way to significantly improve AM-DX performance is
to
remove the entire 4 3/4" x 3/8" stock loopstick, and replace it with a
longer
externally-mounted looptick having comparable coil inductances.
Fortunately,
the ICF-2010 "Supercharging" file (currently posted in dxer.ca's
Ultralight
File section) tells exactly how to accomplish this, in an electrical
manner.
For the ICF-SW7600GR, a hobbyist will need to measure the stock
inductances of the two coils, and either recycle the stock loopstick in a
larger
composite bar augmented by blank 3/8" ferrite bars on the ends, or create
a
self-wound loopstick on 1/2" diameter Amidon ferrite bars (my probable
choice).
Practically speaking, the external loopstick should be limited to a
length of
about 15", since it is unlikely that this hot-rodded SW7600GR would have
a
performance surpassing that of a hot-rodded ICF-2010, even with a longer
loopstick.
It will be interesting to see how this "supercharged" ICF-SW7600GR
performs in the real world. Although not really close to being an
"Ultralight"
radio, it might be useful as a barebones SSB "spotting receiver" for
those
travelers unable to accommodate a more capable SSB unit.
73, Gary DeBock