Gap Dx Eagle VI vertical antenna

[Gary Cox]

A couple of years ago, I purchased a Gap Dx Eagle VI vertical antenna. The
antenna has not worked very well. A few days ago, I borrowed a friend's
MFJ antenna analyzer and recorded the following readings:

Band Freq. Lowest SWR Impedance

40 7.50 1.3 52 ohms

20 15.458 1.0 52

15 21.207 1.5 52

10 28.55 1.2 52

Can someone please help me figure this out. What might I do to get this
antenna working better?
I was trying to figure out, where the SWR was lowest and where it was
nearest 52 ohms.

Sincerely,
Gary Cox, N4LBW
gar...@vnet.net

[Robert Lay]

Hello Gary,

Your problem seems to be very straightforward. I have seen almost the
same characteristics on an R-7000 and an R-7 from Cushcraft. Your
antenna is too short on 40 M and it's too short on 20 M. On 10 M and
15 M it looks OK.

The topmost section(s) of the antenna are the portion that need to be
lengthened. Usually, the manufacturer will provide a handy formula for
correcting length. It will simply be something like 10 kHz per inch
or whatever.

However, there are other things that you may see as you experiment.
For example, I found that on the Cushcraft verticals, the impedance of
the antenna, especially on the lower bands, would change as the
mounting height above ground changed. Furthermore, there can be an
apparent change in the impedance plots as you change the length of the
coax feedline. That's the one that I can't duplicate on a Smith
Chart.

Bob
73 de W9DMK
[Change "nobody" to "w9dmk" for direct replies]

[Clarence R. Carlson]

In article <01bce30a$118c0b60$0eb952a6@default>, "Gary Cox"
<gar...@vnet.net> wrote:

> A couple of years ago, I purchased a Gap Dx Eagle VI vertical antenna. The
> antenna has not worked very well. A few days ago, I borrowed a friend's
> MFJ antenna analyzer and recorded the following readings:
>

SNIP

> Can someone please help me figure this out. What might I do to get this
> antenna working better?
> I was trying to figure out, where the SWR was lowest and where it was
> nearest 52 ohms.
>

> Sincerely,
> Gary Cox, N4LBW
> gar...@vnet.net

Gary:
I am not an engineering type, (I'd probably feel better talking about
somebodies gallbladder) but I do own a GAP vertical. Both the written
material and some advise I got on the phone from the factory said that
these particular antennas very easily detune when around verically
oriented metal objects. Take that into account. Also I like what Gary said
about remembering that the feedline is part of the antenna. Another point,
I know what your SWR readings were, but, really, how much would that
really affect your antennas performance, given that the readings are
accurate and reproducable? Probably not much. We hams often confuse SWR
matching for performance.
Good luck....

WB0FDJ

--
"I saw all the deeds that are done under the sun, and see,
all is vanity and a chasing after the wind.
All that is crooked cannot be made straight,
and what is lacking cannot be counted"
Ecclesiates 1:14-15