[IRCA] Prison Radio Gets Criminally Effective 7" Antenna

[D1028Gary@xxxxxxx]

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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