To John and Others,
The whole concept behind the replacement of the SRF-39FP's stock 1.75"
loopstick was to try duplicating the original coils, coil proportions, and
electrical connections on a much larger scale.
The ICF-S5's 7" long antenna coils were used, but they were rearranged,
tapped, shifted and connected in a manner resembling the original tiny
loopstick's coil connections. From experience, I have discovered that the
best
way to improve sensitivity in these tiny radios is to try "fooling" them, by
connecting an electrically similar but physically much larger proportional
antenna replacement, following the ratio in coil turns as closely as possible.
This strategy worked very well in this experiment.
As viewed from the loopstick side of the circuit board, from left to
right, there are four electrical connections to the SRF-39FP loopstick, as
follows:
1) A connection between the right side of the longer coil and the left side
of the shorter coil (this does not connect to the circuit board; it is simply
a binding post)
2) A connection between the circuit board and a tapped point on the larger
coil (about one-third of the distance from left to right)
3) A connection between the circuit board and the right side of the shorter
coil
4) A connection between the circuit board and the left side of the longer
coil
As long as any experimenter can maintain these electrical connections
and re-create the original antenna's coil proportions and spacing on a much
larger scale, he has a great chance of success, IMHO.
The 7" long antenna from the ICF-S5 parts radio was chopped up pretty
rudely to approximate the coil proportions and positions of the tiny stock
loopstick, then connected exactly as the original antenna was (to the four
connecting points above). Although this was actually just a "first attempt"
to
test out the concept of replacement by a larger proportion "copy," and despite
the fact that the proportions were not completely identical to the original
loopstick, not only did the 7" replacement work great on the first attempt
(with increased sensitivity on both the low and high ends of the band), but it
also had definite alignment peaks, both at 600 kHz (by sliding the larger
coil along the long ferrite bar), and at 1400 kHz (by adjusting the trimmer
capacitor on the tuner).
The new antenna smokes a stock unit both in sensitivity and
selectivity, despite the haphazard connector lengths and coil proportion
approximations.
KPQ-560 is solid copy in the null of KVI-570 on the 7" antenna, but very
marginal on a stock unit. KARR-1460 is quite readable on the 7" antenna in
the
null of mega-local KSUH-1450, but has only the slightest trace on the stock
unit. The 7" antenna also increases the Prison Radio's already great nulling
ability, putting almost all the locals into the noise (on their fundamental
frequencies) during daytime testing.
Hopefully those with the interest to increase stock sensitivity on
their thrilling little Ultralight radios can get some good ideas from the
above
information, and have fun making their little DX terrors compete with any
portable on the planet.
73, Gary DeBock
**************The year's hottest artists on the red carpet at the Grammy
Awards. Go to AOL Music.
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