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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.design
Subject: Re: Sleeve dipoles
Date: Sun, 22 Dec 2024 10:46:03 +0000
Organization: Poppy Records
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Dave Platt <dplatt@coop.radagast.org> wrote:

[...]
> Can you point me to a picture or article which shows this sort of
> construction?

https://kv5r.com    > Ham Radio   > 2-meter sleeve dipole


My reasoning is as follows:

1)  The co-ax is inside the bottom dipole element and close to the
actual radiating conductor, so the sleeve of the co-ax must be at about
the same potential as the corresponding position on the bottom element.
There is no attempt to separate them as there would be with a
large-diameter bottom element or 45-degree  Discone rods.

2)  That dipole is floating on approximately 7ft of insulating plastic
pipe and it appears that the length of the supporting pipe is not
critical.

3)  The feed co-ax comes vertically downwards, not at right-angles to
the dipole.  If the length of the mounting pole is not critical, it
follows that the length of the co-ax is not critical.

4)  Therefore the coax sleeve does not carry standing waves and must be
at earth potential up to the point where it enters the bottom element.

5) Therefore the bottom of the bottom element of the dipole is at earth
potential.

6)  If all the co-ax sleeve below the dipole is at earth potential,
there is no reason why it could not be encased in a metallic supporting
pole.

7)  If the bottom of the dipole is at earth potential, there is no
reason why it should not be electrically in contact with the earthed
supporting pole - or even form a continuation of it.


The end result could be regarded as a quarter-wave whip above a
folded-back ground plane of indeterminate size.

-- 
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk