Antenna reception theory
Asimov wrote:
"An antenna is just a stationary probe in a moving E-field."
Along some path in space there is an electric current which is changing.
It is growing or it is shrinking. It is not constant..
This current as a result of its changes radiates electric and magnetic
flux. The electric flux lines are are perpendicular to the current path.
The magnetic flux lines encircle the current path. The flux is moving
away from the current path at the speed of light. At a distant point
these electric and magnetic flux lines arrive because they sustain each
other during their long trip.
There is an initial wavefront. It started as a spherical wavefront but
has traveled so far that for practical purposes it is now a plane wave.
In the wavefront there is an electric force which would attract or repel
electrons but it has the same strength everywhere over the arriving
wavefront. Therefore, wlectrons in a wire parallel to the wavefront are
not moved along its length by the electric force. This force would only
tend to move electrons from one side of the wire`s diameter to the other
side of the same diameter. Our interest is in current along the length
of the wire.
However, the magnetic lines of force are sweping at the speed of light
across the wire which parallels the wavefront. If the wire also
parallels the direction of the current which generated the lux (is
correctly polarized), it will experience a voltage induced all along its
length. This induction is totally a result of the magnetic field.
Best regards, Richard Harrison, KB5WZI
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