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Re: [TowerTalk] New Cushcraft XM240 Trouble

Subject: Re: [TowerTalk] New Cushcraft XM240 Trouble
Date: Wed, 12 Apr 2006 21:30:57 -0400
List-post: <>
Try grounding the center of the reflector as is
done in the 40-2CD...

73,  Ted  K2QMF

On Wed, 12 Apr 2006 19:42:02 -0500 "Robert Pack (NX5M)"
<> writes:
> 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 3:1. 
> 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 frustrated.
> 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?
> Thanks.
> Bob NX5M
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