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/

It is incorrect.

Snarf


"Nic. Santean" wrote in message news:3f16b377@shknews01...

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/

Now this is what I call a highly detailed answer.
"snarf" wrote in message
.. .
It is incorrect.

Snarf

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

Sorry guys, I have just realized that there are
replies to my posting, which I somehow lost
(from Richard Harrison, for example).

I am using the NNTP server 203.99.143.60
Does this server have problems ??

Nic.

A simple explanation at URL:
http://ihome.cuhk.edu.hk/%7Es016969/physproj/index.htm

Or the math at URL:
http://www.phys.virginia.edu/classes...axwell_Eq.html

Snarf wrote:
"Without sounding like too much of a wise guy, please explain the single
pulse generated during the single electromagnetic pulse generated during
a nuclear or other type of large explosion."

Can`t shed much light though my posting was referenced above.

Had a course in "Non-Sinusoidal Waveforms" 50-some years ago. It
included finding sinusoidal constituents of various waveforms. A single
bang event can excite resonances which decline a certain percentage of
the remaining energy with each cycle. These are called damped
oscillations. These can be generated by simply opening a switch.

But, I am ignorant of neuclear physics. Surely someone in this group has
studied what makes lightning strike when an A-bomb detonates. All
Hiroshima and Nagasaki meant to me was that I might soon be going home.
I soon got to walk through Nagasaki before coming home. EMP was almost
the least of the targets` problems. Over a large area, about all that
was left standing were "fireproof" safes. Nagasaki`s 1940 population was
252,630. Its 1946 population was 174,141. The bomb dropped on August 9,
1945. We thought the Japs richly deserved what they got, and we all
cheered when we heard the news. The life saved may have been my own. The
bombs saved many more Japanese lives than they took.

The amazing thing is that the Japs hesitated after Hiroshima and the
second bomb had to be dropped. It is tragically like the old Jack Benny
joke when the mugger demands: "Come on now, your money or your life,
what`s it going to be?" Benny replies: "I`m thinking, I`m thinking!"

Best regards, Richard Harrison, KB5WZI

Among the numerous effects of a nuclear explosion in the atmosphere are
X-rays and Gamma Rays. These are photons of two greatly different
wavelengths. These photons interact with the atmosphere in a very
complex manner depending on the frequency of the photons. Narratively,
these can be thought of in the following way.

The atmosphere absorbs the photons. The energy in the photons causes
ionization of the air molecules, primarily Nitrogen and Oxygen. The
ionization strips the electrons off of these molecules. This leaves the
nucleus positively charged and creates an electron shower that blasts
away from the nucleus.

So, the electrons, being much lighter than the nucleus, move further
away from the nucleus causing a electromagnetic wave. There is a time
varying electric field between the nucleus and the electrons: and, the
motion of the electrons creates a simultaneous time varying magnetic
field. The electrons 'curve' back to the nucleus to recombine and
produce no net charge in the time period of 10s of microseconds after
the nuclear event.

Now, the X-rays are absorbed by the atmosphere over the distance of
several meters from the blast source. While the Gamma rays are absorbed
over the distance of several kilometers. X-rays and Gamma rays travel at
the speed of light so the resulting waveform of the EM field has a very
fast rise time from the X-rays, a longer rise time for the Gamma rays
and a slower fall time from the Gamma rays.

The EM Pulse has a very fast rise time, typically less than 10
nanoseconds [10 MHz], and a longer fall time typically 10s of
microseconds [ 1 MHz]. A Fourier analysis of the frequency components
shows the EM energy ranges from 100 KHz to in excess of 200 MHz.

So, the resulting EM wave then can propagate in accordance with the
characteristics of the Low Frequency, Medium Frequency, High Frequency
and Very High Frequency propagation characteristics in effect when the
explosion occurs.

Unclassified data indicates the EMP Pulse has field intensities in
excess of 25,000 volts per meter in the HF portion of the spectrum!
[Hmmm ... a ten meter dipole antenna could be in an EM field in excess
of 125,000 volts!! WOW! Talk about ESD susceptibility with the new IC
746 Pro. Not much would survive this unless specifically designed to do so.]

This is a far as I'll go with the explanation.

Deacon Dave, W1MCE

PS: The Rev. Deacon spent many years designing equipment to MIL Specs
including nuclear effects.


[SNIP]
Snarf wrote:
"Without sounding like too much of a wise guy, please explain the single
pulse generated during the single electromagnetic pulse generated during
a nuclear or other type of large explosion."

[SNIP]

Well, at least one thing you guys succeeded :
made me go to the library and start reading.

An initial feeling I have is that equations and
formulas (Maxwell's and alike) do [describe]
these phenomena; however they do little to
[explain] their very nature. Hence, I guess
pretty soon I will dive into quantum physics
to look for some answers.

For example, I needed the Special Theory of
Relativity to get myself convinced of the intrinsic
reality(!) of the electric/magnetic field. And
this was tough, since is hard to comprehend
some form of physical existence without the
support of matter.

Cordially,

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



"Nic. Santean" wrote in message news:3f16b377@shknews01...

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/