[Antennas] RE: Grounded antenna systems

2002年5月23日 17:23:03 -0500

With a metal tower, Pat, it indeed becomes part of the
antenna system if either leg of the dipole is connected
to it - that's what makes antennas like the "sloper" work.
If, on the other hand, the dipole is *isolated* from the metal
tower (or forest service tower) then the metallic characteristics of the
tower only enter "the picture" in terms of destroying the usual dipole
radiation pattern. To the best of my knowledge, there is no "negative side"
of a dipole. If you connect the rig's chassis ground to the metallic tower,
you'll find that it won't change anything except to make the rig
"electrically safer".... The antenna pattern has already been distorted by
the physical presence of the metal tower, and grounding the rig to the tower
won't change the radiation pattern.
As for "grounding" the feedline(s) to a tower, you might want to check out
the Polyphaser Corp. website and their products for grounding (towers,
feedlines and so on). The information is valid and can be taken as
"gospel".
Karl K - W8TIF
McKinney, Texas
-----Original Message-----
From: Pat W
Sent: Thursday, May 23, 2002 4:48 PM
To: [email protected]
Subject: Re: [Antennas] Log Periodic-Grounded antenna systems
<snip>
 I've begun thinking about this subject and have
concurred that grounding the feedline ANYWHERE is not a
good idea.
 I am going to be giving a presentation at the local HR
club and am going to use an example of operating field
day on a 66' metal forest service tower with a 66'
dipole on 40 meters.
 Imagine the dipole is strung such that it intersects
the tower at the 66' level. Now ground the rig to the
tower. Where do you attach the negative side of the
dipole??? To the tower of course. Does this make sense ???
Isn't the tower now part of the antenna system?
SInce the tower is 1/2 wavelength long, it is a dead
short to ground on 40m. On 80 or 20 meters, the tower
is now insulated or isolated from ground.
 Isn't any grounded feedline part of any antenna system?
 Pat W0OPW