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[TowerTalk] New Cushcraft XM240 Trouble

To: "towertalk" <>
Subject: [TowerTalk] New Cushcraft XM240 Trouble
From: "Robert Pack (NX5M)" <>
Date: Wed, 12 Apr 2006 19:42:02 -0500
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I am out of ideas so let me probe the minds here.  I have already been in touch 
with CC on this issue.

Bought a new XM240 a couple of months ago.  Built it to specs for the center of 
the band.  The antenna did not present an swr any lower than 1.6:1.
This past weekend the antenna was taken down and up several times.  The coils 
and balun were checked but nothing seemed to be abnormal.  All connections are 
good.  Measurements were triple-checked before the antenna went up two months 
ago but we checked them again just to make sure.  All are correct.  We even 
changed the tip sections to the upper part of the band setting but still saw 
the same swr 1.6 (only higher in the band as it should be).  
The coax was tested and the antenna was even tested with a different piece of 
coax.  No luck at all.  Finally the balun was bypassed and the coax connected 
directly to the driven element but that did not seem to make much difference.
What I do find interesting and confusing is that at the lowest swr point, or 
resonate spot, the analyzer is telling me that it is 29-30 ohms.  This I do not 
understand.....but it does explain the mismatch.  I also do not understand why 
the analyzer shows 50 ohms at another point in the band but the swr is over a 
Now CC wants me to send the coils back for testing which I guess I will do 
since the antenna is on the ground anyway and somewhat useless to put back into 
the air given the swr issue.  All of this even after CC sent me two new coils 
just in case I found a bad one........which to the best of my knowledge none of 
them are bad.
There are very few failure points on these antennas so I am really confused and 
Based on the 29-30 ohm reading I guess I could always feed the antenna with two 
130 foot runs of 75 ohm cable in parallel........just being silly.  But 
spending what I had to spend to buy the antenna seems the thing should be 
better than this.  The 40-2CD that is on the top of the tower works just fine 
(flat swr at the design frequency).
To me it has to be a coil or the balun.  

Anyone have any helpful ideas?


Bob NX5M


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