TopBand: Top feed verticals?
Mon, 8 Mar 1999 06:27:14 +0800
John Heys G3BDQ has done a lot of work with this kind of antenna - he used
to run an inverted-L, which was earthed at the base of the vertical with
lots of radials and fed via a horizontal wire which ran from the top of the
vertical section into the shack.
John used to feed the antenna with a L-network in the shack, which was in a
upper bedroom of his house. I think his antenna was just over 200' long in
total, maybe a bit less, but the length of the antenna is not critical. If
you make the overall antenna length a quarter wave long, that gives it a
very high Z feed - it is better at three eighths to a half wave in length.
G3BDQ used this system very successfully on the low bands and had one of the
best signals out of the UK on 160m - with only about 50' of vertical. This
arrangement also gives you an excellent all-band antenna.
The only problem you can have with this kind of antenna is that, depending
on the length of the inverted-L, you can end up with RF in the shack. This
is easily solved by attaching a quarter wave radial to the chassis of the
ATU - the radial is best made of heavily insulated wire (you don't want
anyone touching the voltage end of it!!!) and can be wound around the room,
under the shack carpet.
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