TC 9-64 _________________________________________________________________________
alternating current (AC) to flow mostly near the outer surface of a solid
electrical conductor, such as metal wire, at frequencies above the audio
range. The effect becomes more and more apparent as the frequency
increases.
3-28. Copper losses can be minimized and conductivity increased in an RF
line by plating the line with silver. Because silver is a better conductor than
copper, most of the current will flow through the silver layer. The tubing then
serves primarily as a mechanical support.
Dielectric Losses
3-29. Dielectric losses result from the heating effect on the dielectric material
between the conductors. Power from the source is used in heating the
dielectric. The heat produced is dissipated into the surrounding medium.
When there is no potential difference between two conductors, the atoms in
the dielectric material between them are normal and the orbits of the
electrons are circular. When there is a potential difference between two
conductors, the orbits of the electrons change. The excessive negative charge
on one conductor repels electrons on the dielectric toward the positive
conductor and thus distorts the orbits of the electrons. A change in the path
of electrons requires more energy, introducing a power loss.
3-30. The atomic structure of rubber is more difficult to distort than the
structure of some other dielectric materials. The atoms of materials, such as
polyethylene, distort easily. Therefore, polyethylene is often used as a
dielectric because less power is consumed when its electron orbits are
distorted.
Radiation and Induction Losses
surrounding the conductors cause both. Induction losses occur when the
electromagnetic field about a conductor cuts through any nearby metallic
object and a current is induced in that object. As a result, power is dissipated
in the object and is lost.
3-32. Radiation losses occur because some magnetic lines of force about a
conductor do not return to the conductor when the cycle alternates. These
lines of force are projected into space as radiation and this results in power
losses. That is, power is supplied by the source, but is not available to the
load.
LENGTH OF A TRANSMISSION LINE
3-33. A transmission line is considered to be electrically short when its
physical length is short compared to a quarter-wavelength (λ) of the energy
it is to carry.
spelled out in some cases, and in other cases, the numerical value is used.
3-34. A transmission line is electrically long when its physical length is long
compared to a quarter-wavelength of the energy it is to carry. You must
understand that the terms "short" and "long" are relative ones. For example,
a line that has a physical length of 3 meters (approximately 10 feet) is
considered quite short electrically if it transmits a radio frequency of
3-8
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