[TowerTalk] Dipole Centre - Proximity To Metal Mast

[Dudley Chapman]

>Message: 1
>Date: Mon, 30 Jan 2006 23:26:11 -0000
>From: "Jim Martin - MM0BQI" <MM0BQI at blueyonder.co.uk>
>Subject: [TowerTalk] Dipole Centre - Proximity To Metal Mast
>To: <TowerTalk at contesting.com>
>Message-ID: <002b01c625f4$8e3c9220$0201a8c0 at home>
>Content-Type: text/plain;	charset="iso-8859-1"
>
>I have a small garden and just manage to squeeze a 40/80 loaded dipole from
>the roof to the fence.  The centre of the dipole is currently unsupported
>six feet above the flat roof and I would like to increase this to about
>fifteen feet by supporting the centre with a fifteen foot metal mast.  Can
>I secure the dipole centre directly to the metal mast (2 inch diam pole) or
>should I use some form of insulated stand off?  The dipole ends are only a
>foot from the metal end supports, will this be having a detrimental effect
>on performance?
>With this sort of compromise you need to squeeze every bit of advantage
>where you can so your comments and advice on what is actually worthwhile
>doing would be appreciated.
>Thanks
>Jim,  MM0BQI

Jim,
   The center of a dipole is quite insensitive to proximity to metal.  You
could secure the center insulator directly to the metal mast, if you have no
other choice.  Since your antenna might not be completely balanced I would
make sure that the wire elements are electrically insulated from the metal
mast, however.

    The ends of a dipole will capacitively couple easily to any nearby metal
object, especially when the dipole is loaded.  A distance of one foot from
the wire end to the metal support might be close enough to detune your
dipole and.  Hopefully, by raising the center, the ends might be farther
from the supports by a few more feet.

Dudley - WA1X