Kari OH5LF wrote:
>I hope to get some comments. Titanex 160HD vertical is 87.5 feet
>long, I have extended it up to 95 feet. What will happen if I add
>capacitance hat at 75 feet level. The hat is like wheel which has 6
>spokes, each 3,3 feet long (3 mm diameter ). Does it improve
>performance compared no hat at all. Or is the improvment just
>marginal. Two similar vertical will be phased with Comtek coupler.
>Naturally I have to use additionally base loading coil and impedance
>matching (beta coil).
I was doing some EZNEC modelling of a 160m vertical today and thought I'd
quickly change one of the models to see what the impact of the loading would
be. Obviously my model won't fully represent your environment, but the
result should be informative. The model uses four 40m long radials 0.4m
above real average ground. There is 50mm tube for the first 22.9m (75ft) of
the vertical element, then 10mm for the remainder of the 28.98m (95ft).
Without the loading at 22.9m the base impedance is 20.28 -j169.4 ohms and
the max gain is -0.29dbi at 24 degrees. With the loading the base impedance
increases fractionally to 21.05 -j152.5 ohms with a max gain of -0.23dBi at
24 degrees. I wouldn't have thought the difference was worth the added
complexity. Have you considered top loading with sloping wires to bring the
antenna to resonance and get the base impedance up which will reduce (a
little) the impact of ground loss.
Mike
G3WPH
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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