Looking at the weeps , The linear loading wire/element support wire have to
be intact… I think I would look at the 4 turn 3” coil that across the
feedpoint.
Wayne W3EA
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10
________________________________
From: TowerTalk <towertalk-bounces@contesting.com> on behalf of w5wz@w5wz.com
<w5wz@w5wz.com>
Sent: Sunday, September 15, 2019 4:32:48 PM
To: towertalk@contesting.com <towertalk@contesting.com>
Subject: [TowerTalk] 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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|