Owen Duffy wrote:
In my experience, the capacitive reactance of a short vertical is usually
"tuned out" with a series inductor (inductance and resistance).

Owen, he is probably trying to achieve a feedpoint
impedance of 50 ohms instead of a resonant feedpoint
of 20 ohms. If one makes the feedpoint 25-j25, for
instance, and installs a base shunt coil, one can
twist the feedpoint impedance to 50+j0 ohms using
a +j50 ohm shunt coil.

In like manner, a -j50 base shunt capacitor will
twist 25+j25 to 50+j0 ohms.

The ARRL Handbook describes such shunt matching
techniques in the mobile antenna section.
--
73, Cecil http://www.w5dxp.com