Hello, Topbanders
I?ve been mulling over this question for a while in advance of some antenna
maintenance and possible upgrades, but I can?t seem to arrive at a
definitive conclusion myself. So, while things are quiet here, I thought
I?d ask the antenna experts and/or broadcasting engineers on this list.
My current 160M transmitting antenna consists of a vertical radiator 82
feet tall together with an ?inverted U? linear loading section at the
base. The antenna is similar to the one formerly used by ON4UN and
described in the first edition of his book ?Low Band DXing?, except my main
radiator is not a tower, but rather a 6-wire, 37-inch diameter cage
suspended alongside and 3 feet away from the tower. The loading section is
made of ¼? O.D. copper tubing, nested within the cage. The whole thing is
operated over 102 radials, all of which are at least 72 feet long and
longest about 160 feet in length.
The antenna operates on 80M and 40M by switching out the loading
section. 82 feet was chosen as the length (height) to give me a
5/8ths-wave vertical on 40M, though because of the high length-to-diameter
ratio it is somewhat longer than 5/8ths of a wavelength on 40M.
Without the loading section, the vertical radiator alone is resonant at
about 2440khz. With the loading section switched in, the resonance is at
1830khz. It is then matched to the 50-Ohm feedline through a remotely
controlled L-network.
All conductors in the system are copper, and all connections except those
switched by relays in the remote tuner are soldered, to reduce losses.
Now, my question it this: Which is more efficient (less lossy)?
(A) Bringing the antenna to resonance with the loading section, and then
matching to the line with the L-network?
Or,
(B) Matching the non-resonant antenna directly with the L-network, omitting
the loading section altogether?
K5ZK - Charles
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