Richard Harrison wrote:

Yuri Blanarovich, K3BU wrote:
"Have you figured out how to model loading coil of particular
inductance and physical size to reflect the real current drop across
it?"

Current drop across a coil is E/Z where Z is complex. If a reflection is
involved in the antenna, there are multiple Es involved, perhaps.

Growing or shrinking current through a coil, generates a voltage which
opposes current in the coil. Because of its opposing direction it is
called "counter emf". The change in current in the coil generates the
counter emf. A steady d-c current in a coil generates no emf.

A given length of wire has much greater counter emf when coiled than
when stretched out straight. We say it has more "inductance". It`s
because fields from close-wound turns intercouple. With 3 turns
closewound in a coil, 3 times the lines of force cut 3 turns, so 9 times
the counter emf is generated. As a first approximation, the inductance
varies as the square of the number of turns.

Opposition of counter emf in a coil delays the rise of current in a coil
from the phase of an a-c voltage. In a perfect coil with no resistance,
the delay is 90-degrees or 1/4-cycle. Resistance, useful or useless,
reducees the current delay. Due only to the L/R ratio, the phase delay
imposed by a coil can vary from 90-degrees down to zero.

I did a web search on "r.r.a.a" which produced 590 hits. One of these
was something posted by Roy Lewallen entitled "Inductor Operation". Roy
had measured phase delay in a loading coil. If I understood Roy, he
found no phase delay in an antenna loading coil.

In my opinion, he should find delay even in a coil feeding a dummy load,
especially if the coil is large as compared with the dummy load.

Best regards, Richard Harrison, KB5WZI

It might be profitable for you to actually try the measurement. Like
Roy, I also find no delay *across* a physically small coil. The coil
does cause a delay between current and voltage, and as theory would
indicate, that delay (and V/I phase relationship) appears everywhere in
the series circuit, rather than locally across the coil. But, as I
believe Reg and others have suggested previously, as the coil begins to
take on dimensions that are a larger faction of a wavelength,
propagation delays begin to produce additional effects, manifested in
particular by the standing wave profile. In physically small,
inductively large coils, I can find no propagation delay. This is
consistent with the report on W8JI's web page. However I think it's
reasonable to say that as the coil starts to become physically large, it
begins to produce observable delays. These delays appear to be greater
than one would expect for a straight conductor of the same length.
Perhaps someone here can explain why that might be, but I am as yet
unable to. I suspect that it's because as the coupling between turns is
reduced, the coil begins to look less like an inductor, and more like a
compact length of transmission line arranged in the shape of a helix.

73,

Jim AC6XG