Calltrex wrote:

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====================+============================ ½ dipole
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If what you say is true then why draws every antennabook the voltages
like above?
We all know that an amplitude can not be negative in value! So all
books are wrong?
And could you keep the answer at amateur levels pls?

I can't answer for "every antennabook" except to say that any book
showing a graph like that and claiming it's a graph of antenna voltage
is wrong. As Tom K7ITM recently pointed out, you can't determine a
voltage at some point along the wire, as implied by the graph. A voltage
only exists *between* two points, and in the the presence of the fields
around an antenna, the voltage between two points also depends on the
path you take between them -- conceptually, it depends on how you
position your meter leads. You *can* find the strength of the E field
near various points along the antenna (and it looks pretty much like the
graph), but that's not the same as a voltage.

A resonant antenna is one having a feedpoint impedance that's purely
resistive, that is, it has no reactance. This impedance is the feedpoint
voltage divided by the feedpoint current; the feedpoint voltage is the
voltage between the two terminals. The reactance is zero only if the
feedpoint voltage and current are exactly in phase, and regardless of
their amplitudes.

If the terminals are very far apart in terms of wavelength, you have the
same problem in measuring or even defining voltage between them as you
do with points along the antenna. So the common definition makes the
assumption that the feedpoint terminals are very close together.

Roy Lewallen, W7EL