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Re: Topband: To short or not short unused coil turns

Subject: Re: Topband: To short or not short unused coil turns
Date: Tue, 5 Oct 2010 10:34:19 EDT
List-post: <">>
Thanks to everyone that responded to my original question, and below is a  
summary of the responses I received along with a test I performed last  
I did receive a few direct responses to my question about shorting or  not 
shorting unused antennal loading coil turns, and 50% of the  responses 
directly supported my original belief that shorting unused  turns would have a 
negative effect on efficiency, but it was also agreed that  shorting unused 
turns are often necessary to avoid problems with arcing due to  the very high 
voltages generated in the section of unused coil turns.
Last night I ran a simple test in which I selected the loading coil tap  
point for 80 meters operation and compared received signal strength  using the 
unused coil turns shorted versus not shorted (used a local  RF generator as 
the signal source, and my HF rig with my 53 foot vertical and  loading coil 
as the receiver).  My wife watched the analog S-meter on  my HF rig while I 
shorted and un-shorted the unused coil turns and  there was no detectable 
change in received signal strength regardless  if the unused coil turns were 
shorted or not, indicating that any loss in  efficiency due to using shorted 
coil turns was insignificant in my  application.  
My 53 foot vertical currently has 15 buried ground radials and each radial  
is approximately 60 feet long, so its possible that slight changes in  coil 
efficiency were not detected due to the fact that my ground losses  are 
probably much greater than the coil losses which would make the coil  losses 
look small (insignificant) compared with the ground losses.
I repeated this test on 160 meters and again their was no detectable  
change in S meter readings.
My loading coil is 91 turns of the MFJ 404-0669 inductor all in a straight  
line (one continuous coil).  On 80 meters I am using 10 turns of the  coil, 
and on 160 meters I am using 70 turns of the coil in order to obtain  
resonance near the bottom of each band.
Based on my application I will use shorted turns since I was not able to  
detect any changes in performance.
73's and thanks again to those that responded to my original  question.
Don Kirk (wd8dsb) 
UR RST IS ... ... ..9 QSB QSB - hw? BK

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