Richard Harrison wrote:
There is a difference in impedance between the ends of a loading
coil so that the current at its ends are different.

Good point, Richard. Why isn't anyone arguing that the current on
each side of a loading coil in an antenna tuner is equal? It can
easily be proven to be different using a Smith Chart.

"For present purposes" we may declare anything so long as we don`t
define our purposes, but Fig 9-22 on page 9-15 of ON4UN`s "Low-Band
DXing" is significant and no one has said his pictures are wrong and
given reasons.

I haven't seen that book, but I have seen reproductions of his diagrams
on the net. The situation is not as simple as asserting that the coil
occupies the number of degrees not occupied by the vertical sections.
As usual, the facts lie somewhere in between the two rail arguments.

1. The currents at each end of the coil are not equal. (shoots down
rail #1 argument)

2. The current distribution over the entire loaded mobile antenna is
not a standing cosine wave. (shoots down rail #2 argument)

Since the coil is a different characteristic impedance than the vertical
sections, there exist reflections, both ways, from each end of the coil.
Taking four additional sets of reflections into account mathematically
is extremely difficult. That's probably why nobody has ever attempted it.

However, a bugcatcher antenna can be approximated by the following:

---600 ohm feedline---+---1600 ohm feedline---+---600 ohm feedline---open
bottom section loading coil top section

By modeling with EZNEC, I am attempting to ascertain the VF of the
loading coil. That's the only thing standing in the way of a
conventional analysis.
--
73, Cecil http://www.qsl.net/w5dxp


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