Richard Clark wrote:

On Fri, 16 Dec 2005 13:56:12 -0800, Jim Kelley
wrote:


one might be inclined to argue that the voltage induced on a wire should be the same at every
point along a finite length


One might, if it were an exceptionally short piece of wire. Otherwise
it must exhibit some greater reactance than nearly 0 and support a
difference of potential in proportion to the current through it. There
is also the radiation (non-0) resistance to consider (same observation
of a potential difference there too).

You seem to be arguing that the induced potential in the wire is due to
IR or IZ. I don't think that's true. According to JC Maxwell, the
magnitude of the induced voltage and current should depend on the EM
field and on the in situ permitivity and permeability of the wire. As
long as those things are constant along the length of that wire, there
is no reason to expect anything but uniform voltage and current along
the length of the wire. As Roy said, an antenna does not behave the
same on receive as it does on transmit apparently. A receive antenna
does not appear to behave like a transmission line.

Presumably, this all hinges on what is meant, in practical terms, for
"finite length."

Finite here just means small compared to any curvature of the wave
front. Were the wire long enough compared to the distance to the
source, one couldn't expect the fields to be uniform along the length of
the wire.

The "rise" in voltage as the field sweeps
past would be with respect to time,

With respect to what time? The time for the wave to sweep past? What
frequency? The full wave, or its peak? or its average (0)?

It just means voltage as a function of time - like the waveform induced
by the fields of a passing electromagnetic wave for example.

rather than with respect to position.


Position of what?

It means position along the wire - as in the topic of the conversation
you've joined.

I apologize for any lack of clarity on my part.

73, ac6xg