............some "seat-of-the-pants" observations (to use an old aviator expression):
To judge the performances of two similar-sized mobile installations, note the value
of the shunt-C required across the feed-coax to provide good SWR 50 ohm match (or
shunt-L if that option is used).
The more C required (less capacitive reactance), the better [or similarly, the
less L (less inductive reactance), the better].
This method of match is actually a version of the classic "L-match" where the
mobile whip with its loading coil represents either R in series with Inductance, OR
R in series with Capacitance at the feedpoint....depending on whether the loading
coil is tuned slightly Below, or Above the resonant frequency. The shunt C (or L) is
the third element in the L-Match Equation. (Many readers will already know this)
Since standard antenna equations calculate the actual radiation resistance to be
very small in electrically- short mobile antennas, we know that with a perfect
ground, and zero-loss mast and coil, the feed-point resistance would be only the
radiation resistance of a few ohms, perhaps 2 to 5 (W8JI's web page calculates a
15 ft. antenna on 1.8 MHz to be only 1.22 ohms).
Therefore, if the mobile feedpoint was found to have low SWR 50 ohm match with
no shunt element, that would be very bad news........it would mean that perhaps 2
parts out of 50 were radiated, and the other 48 parts were loss! And of course,
here no shunt C (or L) would be required which is the worst news.
Conversely, back to "seat-of-the-pants thinking", the more C (or smaller L)
required, the smaller the feed-point impedance had to have been....meaning less
loss resistance included at the feedpoint.