The recent discussion of shunt feeding towers prompted me to seek some
advice on feeding a 400 foot tower.
A local AM broadcast transmitter is changing to FM and will be closing
down the AM transmitter in about 3 weeks. We have arranged to get the
tower for amateur use until it is dismantled, which may be a month or
two. The tower is 400ft high, or three-quarter wavelength, with an
extensive system of buried ground radials to maximise ground wave.
I want to use it on 160m to work as much dx as possible while we have
it. Not having much experience on 160m I would be interested in comments
on what I can expect in the way of propagation in late August,
September. What are the best times for dx working, best frequencies to
use?
I don't expect too much problem feeding the tower. It is sitting on an
insulated base so I guess the feed impedance will be something like a
quarter-wave ground plane. What concerns me is whether its radiation
angle is best for dx. Would it be better to try to feed it like a j-pole
and try to make just the top half-wavelength radiate. I'm not sure
whether that is a practical idea and what the effect of a half-wave
sitting a quarter-wavelength above a good earth plane is in terms of
radiation angle.
Is there anyone out there with experience using a three-quarter wave
vertical antenna??
Bob ZL3TY
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Bob McQuarrie ZL3TY | Internet: b_mcquarrie@minidata.co.nz
Weenink Road | QRA locator RE57OM
Greymouth 7801 | Phone +64 3 7687388
New Zealand | Fax +64 3 7680240
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