Ian White GM3SEK wrote:

Cecil Moore wrote:
RF current switches from a different kind of behavior than DC current.

True, but irrelevant. You are asking for RF current to switch its
behaviour while still being RF current.

Standing wave RF current does not exhibit the same behavior as traveling
wave RF current. If you understood the formulas, you would understand
my statement.

where Ipk(z) is the peak value of the current at point z. The cos(wt)
term represents the cyclical time dependence of the back-and-forth
movement of electrons; it has no dependence on z.

Therefore, the phase of the standing wave current has no dependence
on z. In fact, for a 1/2WL thin-wire dipole the phase is fixed
at zero degrees no matter what is the value of z.

Moral: Standing wave current phase cannot be used to measure the
delay through a piece of wire, much less the delay through a coil.
But that's exactly what W7EL measured. Now do you see why those
measurements were meaningless?

THE PHASE OF THE CURRENT IN AND AROUND A LOADING COIL HAS NO DEPENDENCE
ON Z. Think about the implications of your statement.

Ipk(z) is simply a scaling factor whose value depends only on the
LOCATION of point z within the antenna. It has NO time dependence.

There is an Ipk1(z) at the bottom of the coil. There is an Ipk2(z)
at the top of the coil. Both of them have NO time dependence.
Therefore, the phase shift between them CANNOT be used to determine
the delay through a coil.

The next issue to describe how Ipk varies with the location z along the
wire. The aim of antenna analysis is to find out what the current
distribution along the wire(s) actually is. All the rest of the
antenna's properties can be calculated from this.

Ipk(z) does not have to be a simple cosine function as you seem to
assume above.

I do NOT assume a simple cosine function. I have said many times that
the fields of the loading coil warps the current waveform away from
the simple cosine function. It puts a bump in the cosine curve but
the fact remains that the current envelope magnitude contains the only
phase information in the standing wave current. Above, you have
essentially agreed with Gene Fuller that zero phase information exists
in the standing wave current except in the magnitude.

A cosine function may be a good approximation for very
simple (or simplified) cases; but when the antenna includes a physical
discontinuity such as a loading coil, Ipk(z) will definitely NOT be a
simple cosine function of distance z. So in general it will not be
correct to bundle the z dependence into the same cosine function as (wt).

I suggest that the standing wave current for each segment of the antenna
can be plotted as has been done at:
http://www.k6mhe.com/n7ws/Loaded%20antennas.htm in figure 3
and that a cosine function can be plotted underneath that curve.
Associating the bottom of the coil with one point on the cosine
curve and the top of the coil with another point on the cosine
curve will allow us to make a *rough* estimate of the delay through
the coil. The cosine curve doesn't disappear - it is just warped
by the current distribution through the coil.

There are several methods of finding the current distribution. If you
choose a method based on forward, reflected and standing waves (which
can be done), the "standing wave" is simply a plot of Ipk as a function
of location z. Ipk(z) is a scalar quantity representing the peak
magnitude of the current, and its only dependence is on LOCATION. It is
not an alternating RF current because it has no time dependence.

Yet W7EL used that current with no time dependence to try to measure
the delay through a coil. I don't recall you objecting.

"Current" remains what it always was: simply the movement of charge
(electrons). If it's an alternating RF current, the cos(wt) term
describes how the charge moves cyclically forward and back past the
observation point. A loading coil, the RF ammeter or the
current-transformer measuring probe all respond to exactly the same
cyclical back-and-forth movement of charge.

Yes, but two RF ammeters gives us a different and more complete view
of reality. In a traveling wave antenna, the two RF ammeters would
read the same value. In a standing wave antenna, the values read
by the two RF ammeters depend upon where they are located. In the
1WL standing wave antenna at: http://www.qsl.net/w5dxp/1WLDIP.GIF,
an RF ammeter located at point B might read one amp. An identical
RF ammeter located at point D will read zero amps.

In the standing wave analysis, the current is still the net movement of
charge, ie the instantaneous difference between the forward and
reflected currents.

There is no net transfer of energy in a pure standing wave. As
Hecht says: "Its profile does not move through space." Nor does
it move through a wire. Here's the above 1WLDIP.GIF wire replaced
by a loading coil.

|----1/4WL---|-1/4WL-|----------1/2WL------------|

------A------B-/////-D-------------fp-------------

An RF ammeter placed at B may read one amp. An identical RF
ammeter placed at D will read zero amps. How can one amp
be "flowing" out of the top of the coil while zero amps
is "flowing" into the bottom of the coil. That is standing
wave current and it is NOT flowing. It is just standing still
as explained by Hecht.

These vary together in time according to cos(wt). It
is not possible to measure the "wrong kind" of current by mistake,
because there is only one kind.

Sorry, you are wrong about that. A look at the equations while
varying 'x' proves your statement is wrong. Please reference what
Hecht said about those equations in another one of my postings.

You have already admitted that there is more than one kind of
current, e.g. DC Vs RF. It's time to admit that standing wave
current and traveling wave current have different equations and
therefore are different "kinds" of current.
--
73, Cecil http://www.qsl.net/w5dxp