Message-ID: <000e01c316ce$89bf5e40$fe79a8c0@PCVONWALTER>
From: "Walter Staubach" <walter.staubach@fen-net.de>
To: rsgb_lf_group@blacksheep.org
Date: Sat, 10 May 2003 10:31:21 +0200
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Subject: Re: LF: Other transmission lines
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Hallo Jim and group,

     what you described is exactly my antenna configuration.
The PA is in my shack followed by a small coil 0,268mH with taps, then a 6m
long insulated wire feeds the 2,7mH rubbish-bin coil, located outside under
a roof of glass. The vertical wire follows.  Additionally to the taps I can
make a fine tuning by moving a bundle of four "steam radio" ferrite rods in
the small coil. All this by comfortably sitting in an armchair, no remote
control required.

73  Walter DJ2LF

-----Ursprüngliche Nachricht-----
Von: James Moritz <j.r.moritz@herts.ac.uk>
An: rsgb_lf_group@blacksheep.org <rsgb_lf_group@blacksheep.org>
Datum: Freitag, 9. Mai 2003 18:29
Betreff: Re: LF: Other transmission lines


>Dear LF Group,
>
>Getting back to the topic of LF antennas, another useful type of feed
>method for LF antennas is the "450ohm unbalanced air line", or, to the
>layman, the "bit of wire hanging in the air". The idea is to have a loading
>coil at the feed point of the antenna as normal, but with about 90 - 95% of
>the inductance required to achieve resonance. This is then connected back
>to the shack by a single wire, where the other 5 - 10% of the inductance is
>located, which is made variable so that tuning can be performed in the
>shack. The feeder can be 10-20m or more, and a couple of metres or so off
>the ground without having much effect on antenna behaviour. The impedance
>that the feeder is operating at is some hundreds of ohms, comparable with
>the Zo of the wire feeder, so loss in the feeder is minimal - analogous to
>feeding an HF doublet antenna with open-wire balanced line. Another way of
>viewing it is as the same as having an elevated loading coil, but with the
>loading coil displaced horizontally instead of vertically.
>
>  The advantage is that the single-wire transmission line only carries a
>few hundred volts, so normal HF wire antenna type insulation where the
>feeder comes into the shack is adequate. This allows you to locate the
>loading coil in the best possible position, and greatly reduces the
>insulation problems, losses, noise pick-up and fire hazard compared with
>having the loading coil inside the shack, while keeping the convenience of
>being able to tune the antenna from the operating position without needing
>a remote control. Since the feed point is located close to the transmitter,
>impedance matching to the TX output can be done in any way you choose
>without worrying about matching to an intermediate transmission line. I
>used this method successfully for some time witth my first LF antenna a few
>years ago. Also, we used this arrangement for the TX antenna on the
>Porthcurno expedition recently, with good results.
>
>Cheers, Jim Moritz
>73 de M0BMU
>
>
>