Re: [IRCA] Prison Radio Gets Criminally Effective 7" Antenna
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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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