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Re: [IRCA] Prison Radio Gets Criminally Effective 7" Antenna
Thanks, Gary,
I think that I understand... I'll report on my mods, too. I really
do think that there is easily improvement possible in many aspects of
the Performance of Ultralights.. and I think that a lot of it is
accessible to people like me, without complete technical competency
AND/OR without a workbench full of sophisticated test instruments. BRAVO!
This is going to be fun.... hey, I'll risk a twenty dollar radio for
the chance to explore my foolish ideas. I've got a DeB-aligned
SRF-39FP and now three totally stock models... Let the surgery begin.
John B.
Stillwater, Oklahoma, USA
Rcvrs: WiNRADiO 313e, Eton e1, NRD-535(kiwa-mods)
Antennas: 700' NE/SW mini-Bev, Wellbrook Phased Array (pre-production version)
At 03:35 PM 2/11/2008 -0500, you wrote:
>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
>
>
>
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