Just as we can make a short antenna resonant by adding a loading coil,
and the loading coil may be placed anywhere along the antenna if an
appropriate coil is chosen, we can make a long antenna resonant by
inserting a series capacitance along the antenna wire.

When that physically long but electrically shortened to resonance
antenna is excited and a standing wave pattern develops, what is the
phase shift of the current through the loading capacitor? Is the
standing wave current on the two sides of the capacitor different, in a
manner similar to how it's different in a loading coil?

If not, why not?

Cheers,
Tom

K7ITM wrote:
Just as we can make a short antenna resonant by adding a loading coil,
and the loading coil may be placed anywhere along the antenna if an
appropriate coil is chosen, we can make a long antenna resonant by
inserting a series capacitance along the antenna wire.

When that physically long but electrically shortened to resonance
antenna is excited and a standing wave pattern develops, what is the
phase shift of the current through the loading capacitor? Is the
standing wave current on the two sides of the capacitor different, in a
manner similar to how it's different in a loading coil?

If not, why not?

Cheers,
Tom


Is it not true that any two conductors can be modeled as either a
transmission line or a capacitor? At this level, there appears to be
analytic symmetry with a series loading coil.

Chuck

K7ITM wrote:

SNIPPED ... Agree a capacitor tunes an 'long' antenna to resonance.

When that physically long but electrically shortened to resonance
antenna is excited and a standing wave pattern develops, what is the
phase shift of the current through the loading capacitor? Is the
standing wave current on the two sides of the capacitor different, in a
manner similar to how it's different in a loading coil?

SNIPPED

What's this current phase shift through a capacitor?

I believe it is a voltage phenomena. The incident and reflected waves
induce voltage at the capacitor terminals. In HF systems the capacitor
is very physically small, and the lumped model should suffice. [There is
no long length of wire to confuse the model].

A vertical antenna has a characteristic impedance, depending on ground
effects, proximity effects, etc. of somewhere between 200 and 500 ohms,
typically 350 +/- ohms.[ It's been a long time since I calculated the
nominal value, but for basic understanding just use antenna Zo]. Apply a
stimulus to the antenna and the signal propagates along the antenna
governed by it's Zo. [Not the Zo of the transmission line at this
point]. So, at the incident input side of the capacitor there is a v
that is the integral of current [incident] times time. This voltage lags
the incident current. At the reflected input side there is a voltage
that is the integral of I [reflected] times time. This current is the
reflected value and spatially delayed by the propagation time from the
capacitor to the end of the antenna. This voltage lags the reflected
current.

The net voltage across the capacitor is the spatial sum, NOTE: Spatial
Sum, of the two voltages. Assuming To at the incident current input to
the capacitor then the problem is simplified to the spatial [propagation
delay to the end of the antenna and return].

So, current phase shift in the capacitor may be asking the wrong question.

K7ITM wrote:
When that physically long but electrically shortened to resonance
antenna is excited and a standing wave pattern develops, what is the
phase shift of the current through the loading capacitor? Is the
standing wave current on the two sides of the capacitor different, in a
manner similar to how it's different in a loading coil?

In order to answer the question, one has to understand the
physics of standing waves. Most people don't understand the
physics of standing waves. Understanding the physics of a
capacitor embedded in a standing wave environment is pretty
much moot if one doesn't understand the physics of standing
waves. Please let's take first things first.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
K7ITM wrote:

When that physically long but electrically shortened to resonance
antenna is excited and a standing wave pattern develops, what is the
phase shift of the current through the loading capacitor? Is the
standing wave current on the two sides of the capacitor different, in a
manner similar to how it's different in a loading coil?


In order to answer the question, one has to understand the
physics of standing waves. Most people don't understand the
physics of standing waves. Understanding the physics of a
capacitor embedded in a standing wave environment is pretty
much moot if one doesn't understand the physics of standing
waves. Please let's take first things first.

You sure use a lot of words to signify the fact that you're
sunk, Cecil, and don't have a clue.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
You sure use a lot of words to signify the fact that you're
sunk, Cecil, and don't have a clue.

The technical content of your posting is duely noted, Tom,
for all the world to observe. Do you really believe that
such an ad hominem gut feeling statement has any impact or
technical value at all? (Rhetorical question)

It reminds me of what an eight year old would say.

If you really want to make a technical impact, please
respond to my tabular data table concerning EZNEC traveling
wave current values Vs standing wave current values.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
Tom Donaly wrote:

You sure use a lot of words to signify the fact that you're
sunk, Cecil, and don't have a clue.


The technical content of your posting is duely noted, Tom,
for all the world to observe. Do you really believe that
such an ad hominem gut feeling statement has any impact or
technical value at all? (Rhetorical question)

It reminds me of what an eight year old would say.

If you really want to make a technical impact, please
respond to my tabular data table concerning EZNEC traveling
wave current values Vs standing wave current values.

Cecil, you've proven over and over again that you're not
interested in technical discussion. You are interested in
argument and a crude sort of digladiation where you do the
verbal equivalent of kicking, biting, hitting below the belt,
rabbit and sucker punching, throwing sand, popping
steroids and amphetamines,and shooting people in the back.
All this is being duly noted by the participants who by
now have consigned your theories to the fractal junk pile.
Come back when you're really interested in a technical
discussion. The kind of discourse you enjoy is only fit
for ending marriages.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
Cecil, you've proven over and over again that you're not
interested in technical discussion.

Allow me to disprove your opinion of me. Please respond to
this earlier posting of mine:

The testx.EZ file has been renamed to:

http://www.qsl.net/w5dxp/TravWave.EZ

The testy.EZ file has been renamed to:

http://www.qsl.net/w5dxp/StndWave.EZ

The current reported by EZNEC for TravWave.EZ contains the term
cos(kz+wt) It's a traveling wave current, clearly not the same
as a standing wave current.

The current reported by EZNEC for StndWave.EZ contains the terms
cos(kz)*cos(wt) It's a standing wave current, clearly not the
same as a traveling wave current.

Current reported by EZNEC every 10% of wire #2 is presented in
the following table. The currents are obviously very different.
The phase of the traveling wave progresses from 0 to 90 deg
in 90 deg of wire. The phase of the standing wave doesn't
progress beyond 0.11 of of degree.

% along current in current in
wire #2 TravWave.EZ StndWave.EZ

0% 0.9998 at -0.99 deg 0.9996 at 0 deg
10% 0.9983 at -9.39 deg 0.9843 at -0.03 deg
20% 0.9969 at -18.23 deg 0.9454 at -0.05 deg
30% 0.9957 at -27.59 deg 0.8843 at -0.06 deg
40% 0.9949 at -35.96 deg 0.8023 at -0.08 deg
50% 0.9945 at -44.84 deg 0.7014 at -0.09 deg
60% 0.9945 at -54.20 deg 0.5840 at -0.09 deg
70% 0.9949 at -62.58 deg 0.4528 at -0.10 deg
80% 0.9956 at -71.43 deg 0.3110 at -0.11 deg
90% 0.9965 at -80.27 deg 0.1616 at -0.11 deg
100% 0.9976 at -89.14 deg 0.0061 at -0.11 deg

Some say "current is current". EZNEC disagrees. When
reflected waves are eliminated, EZNEC indeed does accurately
report traveling wave current. EZNEC reports the current
that is there, whether it is traveling wave current or
standing wave current.
--
73, Cecil http://www.qsl.net/w5dxp