AI4QJ wrote:

"Cecil Moore" wrote in message
.net...
Ian White GM3SEK wrote:
My apologies to AI4QJ. He was talking about a parallel R-L circuit, and
my reply was about a series R-L circuit. Each of our statements was
correct in its own context.

Sorry, but your statement is still incorrect. In a
traveling-wave circuit, the current phase varies
every inch along the circuit path. If it didn't,
rhombic antennas wouldn't work.

First, in response to Cecil:

The behaviour of an antenna doesn't depend on how someone chooses to
classify it. You can apply a traveling-wave *model*, but that is merely
your choice of analysis method. It doesn't change anything about how the
antenna actually behaves.

The challenge for Cecil's model is to explain how the antenna does
behave. This cannot be done by reclassifying the type of antenna, or
reclassifying the type of current through the loading coil.

(And please don't drag in yet another irrelevancy about rhombic
antennas. It'll be photons and momentum next.)

AI4QJ continues:
Yes, the total current will have a phase angle somewhere between zero and
ninety degrees. The vector describing the current through the resistor will
be horizontal to the x-axis. The vector describing the current through the
coil will be perpendicular to the x a-xis. The sum of the currents going
into and out of the R-L network will be the vector sum of the R and X(L)
current vectors (Kirchoff's current law) whose magnitude will be the the
hypoteneuse of the triangle formed by R and X(L) sides with an angle
somewhere between zero and 90 degrees.

(My apologies for the wordiness)

No problem about that; we're all thinking out loud about a difficult
subject, so by all means do whatever it takes to get it right.

I think we are in agreement about the basics. One is the boundary
condition that, If the antenna is loaded at a single point by pure
inductance, then by definition there will be zero phase shift in the
current between its terminals.

Practical antennas move away from this boundary condition because the
inductor occupies an appreciable fraction of the physical length, and
begins to behave more like a short section of helically loaded antenna.
In this case we do expect a phase shift in current from end to end of
the inductor, accompanied by radiation from the inductor itself.
However, any valid explanation of practical loading coils must predict
zero phase shift for the boundary condition where the coil displays no
other properties except pure inductance.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek