IF the reflector is grounded to the boom would the actual length of the
reflector have to be changed a little?
I have never understood why the 40-2CD reflector is grounded and the XM240
is not........basically they are the same antenna.
Still scratching my head on this one.
Bob NX5M
----- Original Message -----
From: <k2qmf@juno.com>
To: <nx5m@txcyber.com>
Cc: <towertalk@contesting.com>
Sent: Wednesday, April 12, 2006 8:30 PM
Subject: Re: [TowerTalk] New Cushcraft XM240 Trouble
>
> 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)"
> <nx5m@txcyber.com> 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
> > 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?
> >
> > Thanks.
> >
> > Bob NX5M
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
>
>
>
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