[LCC] Force 12 EF-240 SWR shift

[Charles Morrison]

I have the Force 12 C4XL which has your EF240 on the same boom as the
tribander, with a separate feedline.   After many years of faithful service,
mine went south as well.  The balun.

The balun filler leached into the SO239 and shorted my input.  Changed it
out with a Balun Designs 1115t.  3-5KW 1:1 balun in a box.. no problems
since.   Worth the money, best baluns on the market.

https://www.balundesigns.com/model-1115-1-1-balun-1-5-54-mhz-3-5kw/

Charlie
N5WE


-----Original Message-----
From: LCC [mailto:lcc-bounces at louisianacontestclub.org] On Behalf Of
w5wz at w5wz.com
Sent: Sunday, September 15, 2019 3:34 PM
To: LCC <lcc at louisianacontestclub.org>
Subject: [LCC] Force 12 EF-240 SWR shift

The SWR minimum on my lowest Force 12 EF-240 has shifted from ~7.16 MHz down
to about 6.7 MHz.  However, the curve appears very similar to measurements
taken and archived in 2015; it's just that it shifted down in frequency.
Examining the antenna with binoculars from the ground, I do not see any
mechanical damage or oddities.

This is a linear loaded type antenna.  It uses a bead-balun, and has a coil
hairpin across the feed point of the driven element.

These measurements were taken in the shack, with the AA-55 in place of the
transceiver; thus the entire transmit RF path is being tested.  I've also
tested at the base of the tower, such that only 125 feet of LMR400, a
PL-259-barrel-PL259 connect, and the PL-259-SO-239 connection at the balun
are involved.  The results are very similar, so I do not suspect anything
amiss that is not up the tower.

I took a sweep of the antenna today and another identical antenna, ranging
from 6.0 to 8.0 MHz.  That data can be found at:
http://w5wz.com/files/40mSCAN

The purple line is the top antenna in the stack, and the blue line is the
bottom antenna in the stack.  Both are Force 12 EF-240.

Lower in frequency = longer elements.  What could have changed to make the
antenna appear electrically longer?

Any thoughts?

--Scott, W5WZ

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