Loading Coils; was : Vincent antenna
Art wrote:
"These are not my laws, they are Maxwell`s"
Yes. They are old butthey still work. Art`s discovery of Gaus has not
replaced Maxwell`s equations.
The origin of Maxwell`s equations may be of interest.
Faraday found that voltage induced in a loop is directly proportional to
the rate of change of the magnetic flux which passes through a loop.
Voltage arises more or less all along the contour of the loop.
Faraday`s law is: V = -dphi/dt
Flux passing through the contour is the integral of the flux density.
The rate of change of the total flux is thus the tate of change of the
integral.
In the years 1856-1873, Maxwell rewrote Faraday`s law by substiturions
to equate the electric field with the changing magnetic flux. The
contour of the magnetic field does not require a current carrying wire
around it.
An electric field is present in space so long as a changing magnetic
field is present.
Another discovery was that the magnetomotive force around a current is 4
pi I. It does not depend on shape or distance in the contour.
Displacement flux is created in a dielectric whenever an electric field
is applied. Electric charges can create it, so it is expressed in
coulombs per square meter. Displacement current is proportional to the
rate of change of the dielectric displacement.
Maxwell knew about displacement current and speculated it would poduce
magnetic flux the same as conduction current does. That was the key to
electromagnetic radiation. If an alternating current flows in a wire, an
alternating magnetic field will be produced in the space around the
wire. The alternating magnetic field creates an alternating electric
field in the surrounding space. This alternating electric field creates
an alternating displacement "current" in the dielectric (maybe it should
be called a displacement stress since the dielectric is an insulator) of
space which gives rise to another alternating magnetic field. This
expanding succession of fields continues ad infinitum. Heinrich Hertz
proved in 1888 that Mexwell`s speculations were correct.
The preceding is presented much more elegantly by B. Whitfield Griffith,
Jr. in "Radio-Electronic Transmission Fundamentals" from which it was
lifted.
|