[Antennas] Vertical

Sat, 28 Sep 2002 15:13:08 -0700

I agree.  Purchase the study by K7LXC
(Champion Radio http://www.championradio.com/forsale/).

Excellent piece of field work but, as I recall, it did not investigate the
'elevation' question.  If I recall correctly, the study reports on ground
mounting of those antennas whose manufacturers  required radials and
elevating (to 30 ft?) those antennas that had their own 'short' radials
(e.g. the CC R-7).  Sort of an apples and oranges comparison but quite
useful nonetheless.

Not sure that changing the feedpoint position on a halfwave length of
radiator (vertical or horizontal) changes the radiation pattern.  Yes, I
would expect it to have a different SWR due to impedance change, but not
sure that means the radiation patterns change.  Did I misinterpret the
point?  Or do I have a technically incorrect understanding of what is
happening?

Seems like the concept behind so called 'short radial' verticals, is that
they are a variation of half wave length (like a vertical dipole) radiator
whose feed point has been physically lowered.  Changes the impedance but
don't believe it changes the radiation pattern all that much.  Just like a
half wavelength horizontal radiator can be fed 'off-center' and still
achieve the same radiation pattern but present a different matching
requirement.  Maybe I have it all wrong.

The WWVH point is interesting.  My first reaction was that it is essentially
a 'ground mounted' vertical dipole (a very inefficient antenna for long
hauls) and that the radials are used to try and achieve an enhanced 'salt
water' like effect of lowering the TO for the primary lobe.  Could be wrong
as I have no first hand knowledge.  Big structure (to handle high power?  to
provide broadbandedness?) but it does not really appear elevated much.  So,
all the more reason to add radials even if they aren't physically attached
to the radiator.  My guess is the extra radials help lower the takeoff angle
of the primary lobe but could be wrong.  Wonder if they elevated that
antenna to 200' if the radials would still be helpful (probably be real
difficult to fed it though).  Perhaps someone has firsthand knowledge and
can clear this up rather than looking at a picture and having to guess.

Thought the latest version of EZNEC (3.0) from W7EL was considered pretty
accurate now.  Would appreciate hearing from anyone who knows otherwise as I
use it quite a bit to model.  Didn't think it had a 6DBi error like earlier
versions of NEC, but wouldn't be the first time I didn't get the word!

73 de Jim WA6PX
[email protected]

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Billy Cox
Sent: Saturday, September 28, 2002 2:26 PM
To: [email protected]
Subject: Re: [Antennas] Vertical

>Might want to read "Antennas Here are Some Verticals on the Beach....."
>by N6BV ("The ARRL Antenna compendium #6", pg 216).

Another good book ... Low Band Dxing by ON4UN ...
Lots of great info to defuse some of the popular ham lore ...

>2-Elevating a vertical, any vertical, even just a little bit, usually pays
>dividends as well.  See "Elevated Vertical Antenna Systems: Is your
vertical system performance up to snuff?  If not, maybe it needs a lift - in
>elevation above ground that is!". (ARRL "Vertical Antenna Classics, KB8I,
>pg108).

Be careful ... here ... there's more than one variable to consider. Raising
the feedpoint on a 1/4 w vertical may change it's impedance ...

The KB8I work has been debated for many years now. W8JI/ON4UN/and
a "7" station did some real world comparisons. Th NEC models are
off by about 6 dB ... so some, that matters not, to most, it matters much.

73 Billy AA4NU

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