There is another thing to keep in mind regarding threatment of
the ends of a dipole. It is true that you will still get good
radiation from a dipole that has the last 20-30% of the ends
hanging down, or that is in some kind of Inverted Vee formation.
This is particularly true on the fundamental half-wave frequency
of the antenna. However, if you plan to use the antenna on
multiple bands, the drooping ends can cause wide variations in
the expected radiation pattern and gain.
Cases in point:
1. If you model a 17M Extended Double Zepp (EDZ) you will find
that its length is almost the same as for a 40M half-wave dipole
(about 66.2' for 17M and 65.9' for 40M). The EDZ dipole is a
powerful performer in its preferred directions and could be
considered in your use of any dipole. The catch is that EDZ
antennas radiate mostly from the ends of the wires, not from the
center. If you drop the ends of the dipole you effectively
destroy the EDZ possibilities. You also will adversely affect
the 15M gain and pattern of this antenna.
2. Another antenna to look at is a 120' 80M dipole (cut roughly
for 3.9MHz). An EDZ for 30M is 118.6'.
There are other interesting and useful combinations to consider
with dipoles that do not have drooping ends. By the way, you
find in modeling the EDZ antennas that gain does not drop off
very much if you are slightly off of the exact EDZ length.
This is just something to think about. Drooping ends certainly
have their place when space is a factor, but don't overlook the
advantages of a dipole that is basically horizontal.
-----Original Message-----
From: topband-bounces@contesting.com
[mailto:topband-bounces@contesting.com]On Behalf Of Herb
Schoenbohm
Sent: Friday, July 25, 2003 8:56 AM
To: Jason Buchanan
Cc: Topband@contesting.com
Subject: Re: Topband: 160 meter dipole polarity
Jason Buchanan wrote:
>
> I am going to hang a 160 meter dipole w/1:1 balun tomorrow and
am
> wondering if there is a recommended method for how to hang it
> "polarity-wise".
Jason,
For a higher performance DX antenna try to get the high current
or
center portion of the dipole as vertical as possible. Even in a
Z
configuration is far better than an inverted Vee. Also dress the
feedline at right angles to the radiator for as far a possible to
reduce
interaction. What you do with the ends of the wire (20 to 30 per
cent
of the overall length) is not critical. The high current
portion,
however, should be vertical or at least semi-vertical.
Herb Schoenbohm, KV4FZ
>
>
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