On Sep 2, 5:52 pm, "John Doe" wrote:

1] The 160m whip assy that I originally planned to use is CENTER-LOADED
which I think is better than a base loaded whip?

Yes it is because the lower (below the load) portion of the antenna
would carry a higher current which increases the radiation
resistance. However, there is no free lunch here, because you must
then provide a larger reactance (More inductance in this case) to
bring the antenna into resonance which is likely to have more loss.
You can push this to extreme too, by doing what you suggest next only
in this case the inductive reactance turns to a capacitor as you pass
the end of the antenna...

2] Someone suggested that I should run a length of bare wire up the tree
and use a TOPHAT. If I decide to go with a 30 or 40 foot length of bare
wire up the tree, How long should the TOPHAT wires be?


Yes, you can add capacitive loading by adding a top hat to the top of
your antenna, thereby reducing the inductance required in your loading
coil. If you can add enough capacitance to your hat, you can eliminate
the inductive loading below, but it can be difficult to get a hat that
large in some cases. Capacitive loading is usually a lot more
efficient than a loading coil and has the added benefit of moving more
of the current up the antenna where it can contribute to the radiation
resistance number (making the antenna more efficient). This "top-hat"
is a set of wires that are roughly horizontal and attached to the top
of your vertical. Make it as big as you can hide in your tree I
suppose and expect to have to add additional inductive loading at your
base to bring it into resonance. Capacitance hats can be hard to hide
though, and difficult to construct.

The ARRL Antenna book would be a very good investment for you I
think. It has a wealth of information about how to figure out how
much your "top-hat" design might lower the resonance of your planned
antenna and how much additional inductive loading you might need. It
also has some nice antenna modeling software that also would help you
with your design ideas. (Instead of having to build and rebuild
possible antennas to find the best performer for your site, you can
model them and weed them down to a few most promising designs to try).

-= bob =-