Brendon,
A capacity hat can work on bringing the frequency downward, but how much
depends on the size of the capacity hat and the inductance of the
loading coil.
If you are not comfortable with modeling software, but have an antenna
analyzer, you can still experiment. Try a capacity hat and see how far
it brings the resonant frequency down. If it is not far enough, try a
bigger hat.
The fact that you can lower the resonant frequency does not indicate
efficiency (it only indicates the ability to properly load the transceiver).
Efficiency and lower SWR are not equal. A 4 foot radiator is still a 4
foot radiator and will have full efficiency at about 50 MHz. Using it
with loading coil and/or top hat on lower frequencies will allow it to
be used, but will not compare with a full size vertical radiator.
73,
Don W3FPR
On 3/24/2016 6:15 PM, Brendon Whateley wrote:
Jim,
Can you toss a capacitive hat on the top of the shorter vertical and see
what difference that makes? I've not figured out how to use the modeling
software yet!
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