> 1. For the modeling guru's, I wonder how my performance would differ
> vs. the "T"?
No one could accurately predict this Les, becuase there are far too many
unknowns. Ground losses most likely dominante the system, since it sounds
like you are forced to use a small ground system. To obtain nearly maximum
possible efficiency, the system probably requires only a reasonable size and
quality loading coil, nothing extreme like a huge nearly-perfect ground
system might require to reach peak efficiency. (Just keep in mind your
antenna's efficiency peak will be at a lower number with a small lossy
ground system!) Q in the low hundreds would almost certainly be enough when
ground losses dominante the system.
The antenna needs maximum possible radiation resistance with a small ground
system, since efficiency would be nearly in direct proportion to radiation
resistance in a system with high ground losses.
Radiation resistance is tied **ONLY** to current distribution in the overall
radiating area of the vertical. You want current as uniform as possible over
the maximum vertical height possible.
That means you must have the most capacitance reasonably possible at the
antenna top, but the capacitance only needs to greatly exceed the
distributed capacitance in the vertical section of the antenna. You need
nothing beyond this, because anything beyond this would have negligable
effect on radiation resistance. If you follow these guidelines, you also can
place the coil anywhere in the system with little or no effect on 160 meter
performance. Following these guidelines, the coil can be at the very bottom
(making it easy to use the antenna on multiple bands with a base-mounted
matching system).
I suggest you model the antenna and look carefully at your bands of
interest. Be sure to follow guidelines in the modeling program you use.
While the results may not be perfectly accurate, it would at least give you
a good feel for effects of any changes in design.
73 Tom
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