On Thu, 17 Jul 2003 10:35:01 -0400, "Nic. Santean"
wrote:


Below is a paragraph - from a known book -
which I have difficulties understanding. Please
somebody explain in more clear terms the
phenomenon.

the context was about dipole antennas,
however the comment has a general nature

"Radiation of electromagnetic waves is created
when the alternating electric and magnetic fields
attempt to collapse back toward the antenna.
However, new fields being created by the next
half cycle push the preceding fields into space,
which is the mechanism of radiation."

- from "The Beginner's Handbook of Amateur
Radio" by Clay Laster, page 260

Cordially,

Nic. Santean
http://www.csd.uwo.ca/~nic/


Hi Nic,

It would seem that there is the necessity of a lag introduced
somewhere for this to make sense. In other words, some delay between
successive emissions of energy.

RF already being time sensitive in the sense of the common 360°
alternation of polarity would suggest that the previous field must not
follow the successive field in time order (otherwise there is nothing
to push as the former has already collapsed in synchrony to that which
follows). This thus presumes that the "first" field found nothing to
impede it; and it pushed free, but began to collapse some distance
out. As it did so, its transit space added lag and the original found
itself in competition with the next field emerging and they both
jostle out like passengers entering an airport moving walkway (or
escalator).

Mind you, this is simply my guess at the intent of the author's words.
I would suspect they are more the product of his having seen or his
having presented you with an illustration of fields that demands this
discussion. You may find this more illuminating if you were to search
for illustrations of field activity close to the antenna (or the
discussion of magnetic lines emanating from the sun).

73's
Richard Clark, KB7QHC

Nic Santean wrote:
"-from "The Beginners`s Handbook of Amateur Radio" by Clay Laster, page
260."

Clay used many words to say the signal propagates too far to get back to
the radiator. It continues its journey away from the radiator.

Radiation is really caused by exchange of energy between alternating
magnetic and electric fields. They produce each other when they
alternate. Static fields don`t radiate. They soon fade away.

J.C. Maxwell speculated that displacement current produces the same
alternating magnetic lines as conduction current does. He was proved
right.

"Static" magnetic and electric fields move out into space when current
flows and charge builds. When they are no longer changing, the fields at
some distance have reached practical limits and stop expanding.
Alternate these fields, and the fields can build each other and travel
on and on.

Best regards, Richard Harrison, KB5 WZI