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[TowerTalk] F12 C4XL 20m "drop" in resonant freq 100hz?

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Subject: [TowerTalk] F12 C4XL 20m "drop" in resonant freq 100hz?
From: "Mel Whitten" <>
Date: Thu, 2 Feb 2012 19:33:01 -0600
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Has anyone experienced a significant (approx 100+Hz) and "sudden" drop in 
resonant frequency for the 20m band -only- on a Force12 C4XL yagi?  This has 
happened to mine (ant about ten years in air with no prior problems). Before I 
climb tower to investigate, is there something specific I should look for that 
may have caused this?   20m is now resonant at 13.980 and was resonant near 
14.100.   SWR is 1.06:1 at 14.000 (Z/R = 51.7ohms) and at 14.330 1.58:1 (Z=64.2 
R=60.1).  The antenna is at 72 feet and not been touched since I noted this 
sudden change in SWR.  Still usable, of course but this change may be an 
indication that something is going bad and may get worse if I don't fix it.  
Weather is very spring like (60s and sunny) in Midwest, so no issues with 
icing.  Looking at elements from a distance, they all look normal. 

Mel, K0PFX
St Louis


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