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[TowerTalk] Measuring KT34 element resonance

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Subject: [TowerTalk] Measuring KT34 element resonance
From: (Larry G Schimelpfenig)
Date: Wed, 03 Sep 1997 19:24:37 EDT
Please excuse a bit more bandwidth on this subject. A number of folks
asked how I measured the resonant frequency of each element.  Several
asked what readings I ended up with.

I used the AEA HF analyst connected to a chunk of RG58. I simply
connected the center conductor to one element (machine screw) and the
braid to the other.  You obviously have to remove straps where present.
On the forward driven element I measured at the point that the balun
connects to the T match.  I'd set the analyst for some point above or
below the band and use wide resolution to find the dip. Then I'd narrow
it up until I could see at which frequency I had minimum swr. You could
do the same thing with very low power and a sensitive swr bridge.  The
problem is that most frequencies end up outside the bands.

If you are having a problem like I did, the first thing I would do is
plot the swr curve on each band taking a reading from the bottom to the
top of the band at each 50khz point.  You shold find two dips on each
band as seen in the manual. Note at which frequency those dips are. 

In my case I noticed that my curve on 15 looked ok, it was simply
centered too high in the band. After playing with the joint that I
discussed in earlier mail, I could see that minimum swr on the rearmost
driven element dropped from 20740 to 20580 and that of the other driven
element dropped from 21700 to 21600. It was at that moment that I knew I
had beat the devil!

I would expect that due to a variety of reasons, the resonant frequencies
you see may vary some from what mine ended up being. The critical point
is that I developed a reference to work against. 

Interestingly enough, after working with "THE JOINT", I saw major
frequency change (at least 100khz) on 6 band elements and a 50khz change
on a 7th. What I mean by that is that is the frequency dropped at least
100khz on every element on 15 meters, dropped 100khz on the first
director on 10 meters and dropped 50khz on the forward driven element. 

I am not comfortable in listing the frequencies I ended up with, because
in some cases they don't make a lot of sense.  I expect that is due to
the fact that the interaction between the triband elements once mounted
on the boom causes a variety of effects that wouldn't be seen on a
mono-band antenna. I wouldn't want to mislead anyone. 

All I know, is that my XA is back to it's good old self again. Don't tell
it so, but at one point Saturday night I had visions of what a hack saw
could do to it. All is forgiven, and once again I love the bugger!

If anyone really wants the dimensions let me know.

73 de Larry K7SV

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