LF: Top load coil at ground level?

[Dick Rollema <dickrollema@casema.nl>]

It seems that some computers could not 
open the attached diagrams  in my previous e-mail..
I therefore send send them again as part of the message itself. Hope this
helps.
73, Dick, PA0SE

To All from PA0SE,

By chance I came across
an interesting article in the Dutch weekly (!) magazine Radio Expres
of 11 January 1934. It referred to an article in the Proceedings
of the IRE of December 1933 by Nickle, Dome and Brown on a procedure
to increase of the feed point impedance of a vertical antenna by means of
top loading. A normal way is to use a series resonant circuit as in
fig.1, consisting of a capacitive hat and a coil. The coil is in a
awkward position for tuning. The alternative by Nickle, Dome and Brown is
to use a short circuited stub slightly shorter than an quarter wave that
at its top end produces the proper inductive reactance for series
resonance with the capacitive hat. Indicated in fig. 2a. The system is
tuned by moving the short circuit at the bottom up or down. The left leg
of the stub is doubling as the radiator. An easier way of tuning is to
make the stub too short and lengthening it with a coil(b) or a stub that
is too long and shortening it by a capacitor (c). I modelled a quarter
wave vertical for 80 m according to (c) using Antenna Optimizer by Brian
Beezley, K6STI. When in resonance the feed point impedance was raised
from 36 ohm without top load to 4925 ohm! The radiation diagram was
identical to the one for the unloaded vertical within a few tenths of a
dB.

It occurred to me that the system could perhaps also be used for a 136kHz
vertical. Using system (b) in fig.2 the loading coil between top of the
radiator and topload could be at ground level. The stub functions as a
transmission line to transfer the inductive reactance of the coil to the
top of the radiator. Of course a second coil could be inserted between
bottom of the stub and ground for matching and feeding of the
antenna.

What do you think?

73, Dick, PA0SE