"Richard Clark" wrote in message
...
On Tue, 15 Sep 2009 11:52:19 +0100, "christofire"
wrote:

No, you have it wrong again - the current must be zero at the ends, there
is
nowhere for it to go, and there cannot be acceleration of charge is
there's
no current. Please go away and read some books and the NEETS module to
which I provided the link.

Chris

Hi Chris,

This mistake is being compounded daily, so it seems. The "absence" of
current on any particular portion of the antenna is the superposition
of two currents flowing - hence the term "standing wave antenna."
Hence there is something of a paradox that where two currents reside
(the metal elements are continuous and conductive) it is said no
current flows. There is a correlation between this superposed
solution and the pattern of the far-field pattern but that does not
lead to the conclusion that there is no "acceleration" of charge at
the ends. After-all, the abundant alternating voltage at those same
ends is also charge, n'est pas? It could be as easily argued that
superposed voltage nodes also define the pattern of the far-field
pattern.

73's
Richard Clark, KB7QHC


Well, the moment of a section of a dipole is proportional to the average net
current on it and it's the integral of the moments at a point of inspection
that yields the radiation pattern. In my simplistic way of thinking, if the
moment of the end sections is zero, or as close as makes no difference, then
there's no contribution to the pattern from there, so there's no radiation
from there. Someone else who posted here a while ago used the term
'unopposed' current which is useful because it's the basis of why twin-wire
transmission line, driven differentially, is a poor radiator - put another
way, the moment at any point is close to zero. Alternatively, if there's no
radiation from a 'source' then there can't be any unopposed current there.

I wouldn't contradict what you say about there being a collection of charge
at the ends of a dipole during each cycle, especially when it has added
capacitance (e.g. a 'hat' or the top of a 'Tee'), but the current in a
symmetrical hat is fully opposed and, as I noted before, the current at the
end of the conductor must be zero - by the definition of conduction.

I believe there is danger in trying to relate radiation to voltages rather
than currents, arguing that displacement current causes radiation. Therein
lies the fallacy of the CFA, E-H antennas, and associated efforts at
re-writing of Maxwell's equations, which are all being demonstrated as bunk.
Also, this appears to be the basis of Mr. Bialek's lecture series. If you
wish to argue 'that superposed voltage nodes also define the (pattern of
the...sic) far-field pattern' then I won't stand in your way ... but I
probably won't believe you.

Chris