Hi Tony,
If you want to do a bit of reading there are plenty of articles which
explain your results very clearly.
For a comparison of capacitive hat versus inductive loading take a look a
the ARRL antenna book. In the 19 edition this is figure 33 and read pages
6-18 through 6-21. Other editions have it also but probably on other pages.
If you can get ahold of a copy of Ed Laport's book "Radio Antenna
Engineering", read pages 18-33 for a good explanation of short antennas and
loading.
Laports work is brought into the ham sphere by Bruce Brown's Antenna
Compendium vol. 1 article, "Optimum Design of Short Coil Loaded HF Mobile
Antennas, Pages 108-115.
A similar but much earlier article is the one by J. Belrose, " Short
Antennas For Mobile Operation", QST, September 1953.
If you are anywhere near a University with an engineering library you should
be able to find older issues of the Institute Of Radio Engineers (IRE)
proceedings. The granddaddy article for top loading using guy wires is:
C. Smith, Performance Of Short Antennas, IRE proceedings October 1947, Pages
1026-1038.
Not hard to follow and very informative. There is a follow up article which
adds some information:
L. Smeby, Short Antenna Characteristics - Theoretical, IRE proceedings,
October 1949, pages 1185-1994.
Most of this stuff is not hard to follow and will give a very good idea of
how loaded verticals work.
Good luck.
73, Rudy Severns N6LF
|