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