Roy, W7EL addressed several provocative questions to Cecil. Anyone can
comment, so I will.

Roy wrote:
"And where those coulombs are going that go into one end of the inductor
and don`t come out the other."

Coulombs travel back and forth in an inductor and may go actually
nowhere. Their movement in an unshielded inductance may result in
radiation and certainly produces some heat.

The purpose of a loading coil in a short loaded vertical antenna is
often to add to the existing degrees of antenna length to reach a
resonant length of 90-degrees, as shown in Fig 9-22 of ON4UN`s "Low-Band
DXing", and included on Yuri`s web pages.

Fig 9-22 is illustrative. First, a full-size 90-degree vertical is
shown. Current is maximum at the base and zero at the top. This is also
true for what Kraus calls a "normal-mode helical antenna". A normal-mode
helical antenna has its principal radiation at right-angles to the axis
of the helix.

The normal-mode helix is fed from a generator with two terminals. One
terminal feeds the base end of the helix directly. The other generator
terminal feeds the ground end of a capacitance between the ground,
various turns, and the tip end of the helix.

The impedance is only a few ohms at the ground end of the helix and
perhaps several thousand ohms at the tip end of the helix. This means a
lot more amps at the ground end of the helix than at the tip end, though
the power flow through the generator`s terminals is the same in either
terminal.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
The purpose of a loading coil in a short loaded vertical antenna is
often to add to the existing degrees of antenna length to reach a
resonant length of 90-degrees, as shown in Fig 9-22 of ON4UN`s "Low-Band
DXing", and included on Yuri`s web pages.

In order for a current maximum to exist at the feedpoint of a shortened
(less than 1/4WL) vertical, the forward current must undergo a phase
shift of 90 degrees, followed by the 180 degree phase shift from being
reflected by an open circuit, followed by another 90 degree phase shift
in the reflected current wave. An 8 foot whip gives about 11 degrees of
phase shift end to end on 75m for a total of 22 degrees. If the coil
causes no phase shift, where does the other 338 degrees of phase shift
come from?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
Richard Harrison wrote:
The purpose of a loading coil in a short loaded vertical antenna is
often to add to the existing degrees of antenna length to reach a
resonant length of 90-degrees, as shown in Fig 9-22 of ON4UN`s "Low-Band
DXing", and included on Yuri`s web pages.

In order for a current maximum to exist at the feedpoint of a shortened
(less than 1/4WL) vertical, the forward current must undergo a phase
shift of 90 degrees, followed by the 180 degree phase shift from being
reflected by an open circuit, followed by another 90 degree phase shift
in the reflected current wave. An 8 foot whip gives about 11 degrees of
phase shift end to end on 75m for a total of 22 degrees. If the coil
causes no phase shift, where does the other 338 degrees of phase shift
come from?

Some people thought I was disagreeing with Richard. I wasn't. I was
agreeing with him and adding another reason why he is right. Incidentally,
the 338 degrees above should have been 158 degrees. I forgot to subtract
the 180 degree current phase reversal at the end of the standing-wave
antenna. Since the coil is the only other thing in the circuit, it
must necessarily contribute that 158 degrees, 79 degrees in each
direction.
--
73, Cecil http://www.qsl.net/w5dxp



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