Jim & LFers
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.
I have always used this system and find that it works very well. I didn't
have a name for it and just referred to them as the matching and tuning
circuit and the loading coil. In my installation the two are displaced by
around 2m with the "bit of wire hanging in the air" just over 2m high. I had
never thought of it as a transmission line.
With the arrangement used at Amberley museum the two components were
displaced by around 8m.
Just a thought. Where should you connect the system to ground if the two
components are some distance apart? Conventional wisdom suggests it should
be under the loading coil.
Regards,
Peter, G3LDO
e-mail <[email protected]>
Web <http://web.ukonline.co.uk/g3ldo>
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