Jim Brown wrote:
>> My 160M antenna is 86 ft vertical with a lot of top loading and 60+
> radials. People tell me I'm loud. My top-loading makes it electrically
> longer than a quarter wave so that it looks inductive (50 + j200 or so),
> and I tune the j200 out with capacitance.
>
> 73,
>
> Jim K9YC
>
Just wanted to second what Jim said. I also have a 90 ft vertical
(for 160 meters) with top loading that is resonant a little below the band
edge and tuned upward with a series capacitor. It is over a 230 foot
diameter ground screen. I also have people tell me I'm loud. The top
loading increases the radiation resistance about 50%. By using more
top loading than is necessary to attain resonance, I move the current
maximum up above ground and further increase driving resistance.
This same antenna on 80 meters has about 1000 ohms drive impedance
at the bottom.
The top is guyed with four pieces of baler twine coming down
at about a 45 degree angle. The top loading wires are 30 feet long
and are ty-rapped to the guy ropes.
If you only have 43 feet, by all means add top loading if you can.
It is easy to model top loading with EZNEC.
Rick N6RK
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