Hopefully your skills extend beyond looking up values in books, to being
able to do actual calculations. Given the measured antenna impedance I
reported and the inductor I used, what should we expect as the ratio
(magnitude and phase) of output to input current at the two inductor leads?

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"Other predictions would be welcome, too, such as Yuri`s based on the
"missing antenna length" theory of inductor current."

It`s desirable to resonate a standing-wave antenna to reduce impediment
to antenna current.

In the 19th edition of the ARRL Antenna Book, there is a section on
"Base Loading and Center Loading" beginning on page 16-4.

First point is that current is not uniform in a ground mounted whip
because the bottom section of the whip is closest to the ground, and so
has more capacitance to the ground.

Next point is that raising the coil up in the whip improves current
distribution. The high voltage which boosts capacitive current is moved
farther away from the earth or ground plane. Lower voltage below the
coil has less capacitive current between the earth and whip than before
the coil was boosted. Current below the coil is now almost uniform.

Table 1 gives coil values for base loading and center loading an 8-ft
whip in amateur bands between 1.8 and 29 MHz.

There is a CD-ROM attached to the rear cover of the ARRL Antenna Book
which includes a program, MOBILE.EXE, for optimization of coil
placement.


There is much practical information in this Antenna Book section. I`d
speculate it was tried and proved useful before it was included in the
Antenna Book. Has anyone found faults?

Best regards, Richard Harrison, KB5WZI