There is also the issue of reduced skin depth and extra losses when
using steel wire, or any other magnetic material for that matter. Skin
depth reduces as the square root of relative permeability, which for
steel wire is several thousand.
Did the modelling of the MF atnennas take this magnetic wire effect into
account, although at those frequencies much of the current will be
concentrated in the zinc galvanising so reducing the Ur losses.
As you say, the high impedance of these antenna will not show up the
losses in the wire nearly as much as using steel wire at LF where skin
depth is 0.2mm or so.
Andy G4JNT
----------
From: vernall[SMTP:[email protected]]
Reply To: [email protected]
Sent: 2000-06-30 07:46
To: [email protected]
Subject: Re: LF: Wire, for LF Antennas
Larry,
Mentioned for completeness, at the Quartz Hill ZL6QH DX station, of
which I am a member, we decided to use high tensile 12 gauge
galvanised
steel wire for replacement of any of the long Vee antennas. Legs are
typically 250 to 300 metres long. We modelled the situation and found
that losses were only fractional compared to using hard drawn copper.
Some have been installed for over a year, and Wellington has a
reputation for being "Windy Wellington". The 12 gauge high tensile
galvanised steel wire is in regular use for fences on New Zealand
farms,
so is cheap and available.
The ZL6QH Vees are all fairly high (surge) impedance wires at the
MF/HF
bands and that is why a few more ohms of surface resistance does not
give rise to a significant loss factor.
An LF antenna may well be a low resistance affair where series
resistance in the "top loading" is significant, at least for
transmitting efficiency. I think another reply on the reflector
mentioned using copper for an "upwire" and galvanised steel for the
top
loading. In terms of "bang for buck" it could pay to concentrate on a
higher upwire than wider top loading.
73, Bob
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