basic question about radio waves
 

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/

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

Nic. Santean wrote:
Please opinionate : does this get close to an intuition
about radiation?

The RF energy from the source accelerates and decelerates free electrons.
The changing energy levels of the free electrons causes the excess energy
to be radiated as coherent photons.
--
73, Cecil http://www.qsl.net/w5dxp



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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

The "pulse" is the envelope of the RF energy. Lots of frequencies more like
white noise actually, start suddenly, trail off not quite so quickly.
Similar to a radar pulse. Two things. RF, pulse modulated.
Omnidirectionally radiated. Does that help?

--
Crazy George
Remove NO and SPAM from return address
"snarf" wrote in message
...
Without sounding like too much of a wise guy, please explain the single
electromagnetic pulse generated during a nuclear or other type of large
explosion.

Does a certain degree of oscillation (ringing) occur to explain the vast
distances travelled by what one would assume was a single large pulse?

Snarf


"Richard Harrison" wrote in message
...
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

I thought that only light (and not radio waves) has a dual nature.
Are U sure that photons play a role in radio waves radiation ??
U sure?

Nic.

The RF energy from the source accelerates and decelerates free electrons.
The changing energy levels of the free electrons causes the excess energy
to be radiated as coherent photons.