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)"
> 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
> thing.......best 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?
> Bob NX5M
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