Gene Fuller wrote:
Cecil Moore wrote:
Kraus says: "It is generally assumed that the current distribution
of an infinitesimally thin antenna is sinusoidal, and that the phase
is constant over a 1/2WL interval, changing abruptly by 180 degrees
between intervals."

Kraus says something quite similar in the second edition of "Antennas".
(I believe you are quoting from the third edition, which was co-authored
by someone else.)

However, Kraus is merely being careless with terminology. (It is likely
that he did not fully anticipate that he would be quoted out of
context.)

It is within the context of physics. It is only out of context
when the context is sacred cows and old wives' tales.

If one studies the accompanying diagrams it is clear that
Kraus is simply referring to the standard functional form of a
sinusoidal curve. For reasons not clear to me he decides to call the
natural progression from positive to negative as the sine function
passes through zero an abrupt 180 degree phase change. This is
misleading at best.

Kraus is merely following convention. The sign of the real part of the
current at 89 degrees is positive. The sign of the real part of the current
at 91 degrees is negative. A positive sign indicates current flowing in
one direction. A negative sign indicates current flowing in the opposite
direction. Since there are only two possible directions in a wire, those
two directions are 180 degrees apart, by definition.

A true phase change would be, for example, an abrupt transition from +1
to -1 in the sine function. This sort of phase change is used in
numerous communication schemes, such as PSK31.

A true phase change would also be, a smooth transition from +0.001 through
zero to -0.001. When current equals zero at a standing wave node, the phase
of the real component of current on each side of that zero is 180 degrees
different. For the real component of the current, a 180 degree phase reversal
occurs between 89 degrees and 91 degrees. Cos(89) = +0.017, Cos(91) = -0.017
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----