[Top] [All Lists]

Re: [TowerTalk] elevated short vertical dipole or quarterwavemonopole?

To: "Jim Lux" <>,"Towertalk" <>
Subject: Re: [TowerTalk] elevated short vertical dipole or quarterwavemonopole?
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Thu, 2 Dec 2004 18:50:54 -0500
List-post: <>
> You could either put up a standard 1/4 wave monopole with
ground wires, etc.
> The ground radial array is going to be non-optimal, and
moderately lossy.
> Maybe 10-20 ohms loss? Rr would be around 30-35 ohms (or
pretty close, I
> would assume, depending on the diameter), so the system
would be 60-70%
> efficient.
> Or, you could put up a loaded vertical dipole  that's 1/4
wavelength long(so
> the feed point would be 15-16 feet off the ground).
Ballparking it, you'd
> need about 16 uH of loading, and some matching to get the
> reasonable. Rr=13-17 ohms (1/4 that of a halfwave dipole),
if Qcoil=400, X
> is about 700ohms, so Rcoil=2 ohms.  You'd have some loss
in the loading
> coil, however, you wouldn't have the loss in the ground
radial array.

You're neglecting or ignoring the fact that the earth itself
has significant loss because of the high field intensity.

You also have to get the feedline away from the dipole with
making the feedline part of the antenna, and that's no easy

You also could end-load the dipole and have about the same
radiation resistance as a quarter wave antenna.

Too many variables!

I made quite a few actual FS measurements when MFJ and
HyGain were doing no-radial verticals. Antennas were in the
clear, nothing else around. Feedlines were properly

As a general rule (although I'm sure there are exceptions) I
found a 1/4 wl vertical with a modest ground of 15-30 1/8th
wave radials was a few dB better than the best vertical
dipole of the SAME tip height I could build, and I didn't
have the horrid feedline isolation issues with the Marconi

If you have a very poor ground system, a short vertical
dipole would probably be better.

If you can do anything reasonable at all in a ground system,
the same height Marconi would be more effective.

A 1/4 wl vertical dipole with GOOD hats on each end for
loading and no ground radials at all was about 5-7dB down
from a 1/4 wl vertical with 50 radials.

73 Tom


See:  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>