[Top] [All Lists]

Re: Topband: Non-resonant receive antennas

To: "Richard Karlquist" <>, <>
Subject: Re: Topband: Non-resonant receive antennas
From: "Tom W8JI" <>
Reply-to: Tom W8JI <>
Date: Sun, 21 Dec 2014 13:50:14 -0500
List-post: <">>
When talking about a low dipole, the question comes up
as to why it must be low to work.  Actually we don't
know that it must be low to work.  Very few of us are
in a position to put up a "high" dipole, so the question
is basically moot.  However, in an attempt to gauge the
influence of height, I A/B'ed two full size dipoles at
30 and 60 foot heights over a period of 6 months.  The
one not in use was floating to avoid interaction with
the active one.

I never noticed any difference in receiving performance.
What seems to happen is that the signals are a few dB
higher on the 60 foot wire, but the noise is commensurately

Low is always in wavelengths, feet are too general. :)

Your results are expected, because anything below 1/8th wave has little difference in pattern (except for loss of efficiency at low heights). On receive, only the pattern (and polarization) matters until you get into system internal noise floor limitations.

The idea a really low dipole is quieter or has better high angle signal is a big problem with NVIS antennas and emergency services. People park 80 meter dipoles at a few feet and they are no quieter except for loss of efficiency (and in some poor installation cases less feedline radiation at low height).

I had dipoles at ~300, maybe around 130-150, and 60 feet on 160, as well as non-resonant low dipoles. Once below ~150 ft, they all pretty much work the same except for gain reduction with reduced height. That gain reduction can be somewhat mitigated with a ground screen of some type, until the antenna gets too close to the screen.

During the rare times the any dipoles were working very well, they all pretty much "worked". The high dipole was closer to the vertical than the low dipoles at other times.

Of course inside a few hundred miles was different. The high dipole, like the verticals, were dogs. Any dipole below ~150 ft was pretty much the same in close on sky wave.
Topband Reflector Archives -

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