"Wimpie" wrote in message
...
The reason that you don't need to take magnetic dipole radiation into
account in real mechanical systems is because of the radiated power is
very low (low RPM in practical mechanical systems). Friction
(bearings/air, eddy current, etc) is orders of magnitude more then the
"friction" caused by the EM radiation.

Further proof, if any were needed, that a short antenna is a poor radiator.

(Frequencies of mechanical rotation representing wavelengthe of several
miles, against which the length of the magnet is trivial, and why, in the
case
of the superconductor example, there is no measurable decrease in
rotational speed, in the short term, at least.)

El 10-11-14 0:32, escribió:
wrote:
El 09-11-14 23:01, escribió:
wrote:
El 08-11-14 8:03, escribió:
In rec.radio.amateur.antenna wrote:
"Brian wrote in message
...

His whole grasp of antenna theory is flawed.
He was trying to (indirectly) argue the other day via his his
interpretation of Maxwell's Equations you could generate an EM wave
by waving a magnet about. When corrected, he introduced another
variation.

Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your
posts these days are personal attacks aimed at one or another.

Why do you behave like that?

Certainly, as I corrected myself, if you wave a magnet about fast enough,
say, 1000,000,000 times per second, you will certainly generate an EM wave
and no-one has corrected me on that point because that point is true.

No, that point is utterly, completely, and absolutely false and goes
once again to show you have no clue as to the difference between an
electric field, a magnetic field, and an electromagnetic field.



Without doing the math, can we be sure that there is no radiation from
a rotating magnetic dipole?

You could ask someone who understands the math.

It is not that I don't understand the math, but I don't want to spend
time if we can get an answer by using reciprocity (the part of my text
you skipped).

Back to reciprocity:

When using reciprocity, a permament magnet will rotate in an EM
radiation field (produced by an antenna-transmitter combination, far
field distance). Of course you need to spin-up the magnet as you don't
have a rotating field. Once it is synchronized, you can extract power
from it (resulting in a slip angle).

So the other way around, using reciprocity, the rotating magnet will
generate power in a load connected to the antenna that was used to
generate the EM field.

None of which has a permanet magnet spinning in empty space, which is
why I snipped it.

If we can't prove that reciprocity (or other assumption) doesn't hold
for this case, then the rotating permanent magnet produces EM radiation.

And rigously proving any of that is much more complex then F=ma.


Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.


--
Wim
PA3DJS
Please remove abc first in case of PM

"Sn!pe" wrote in message
.uk...
Wimpie wrote:

[...]

Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.

Would such radiation *propagate* though? I have a vague recollection
from many years ago that there's a difference between a proper *radio*
wave and another sort of oscillating field that one also gets close to
an antenna. Was it something to do with the phase relationship between
the electric and magnetic components of the field perhaps?

I may well have imagined this, it was a very long time ago.

What you appear to be discussing is the difference between the Near Field
and the Far Field

Wimpie wrote:

snip

Jim, I would encourage you to dive into rotating magnetic dipole
radiation.

You mean like in a pulsar?

For practical electromechanical systems (even in practial vacuo) it is
negligible as (c0)^5 is in the denominator and (2*pi*rev/s)^4 is in
the numerator, but that doesn't mean it isn't present from a
theoretical point of view.

Again, not talking about any "electromechanical system", just a permanet
magnet spining.

Also implied is the macro level, i.e. a magnet one can hold in one's
hand and velocities well below any relativisitc effects.


--
Jim Pennino

Wimpie wrote:

snip

On an astronomical scale things are different.

Yep, and the discussion is not about pulsars or astronomical phenomena,
it is about magnets one can hold in their hand.



--
Jim Pennino

gareth wrote:

snip

Further proof, if any were needed, that a short antenna is a poor radiator.

All the proof so far having acutal numbers has been that "a short antenna
is a poor radiator" is arm waving nonsense, gas bag, and all you have
presented so far is arm waving and no numbers.



--
Jim Pennino

wrote in message
...
All the proof so far having acutal numbers has been that "a short antenna
is a poor radiator" is arm waving nonsense, gas bag, and all you have
presented so far is arm waving and no numbers.

Grow up, child.

gareth wrote:
wrote in message
...
All the proof so far having acutal numbers has been that "a short antenna
is a poor radiator" is arm waving nonsense, gas bag, and all you have
presented so far is arm waving and no numbers.

Grow up, child.

Show some numbers, gas bag.



--
Jim Pennino

On 10/11/14 18:46, wrote:


Further proof, if any were needed, that a short antenna is a poor radiator.

All the proof so far having acutal numbers has been that "a short antenna
is a poor radiator" is arm waving nonsense, gas bag, and all you have
presented so far is arm waving and no numbers.



It is worse than that, he has dismissed solid theory and tried to
replace it with his nonsense. Just as he has done in the rotating
magnetic thread. In fact, this is his normal mode of operation, he
has a long history of such quackery. The pattern is always the same.
Post some nonsense theory, often dressed up as being something that
has troubled him or he has been studying. The theories are often
rambling nonsense- suggesting any studying has been limited to a 'scan'
of a few key terms. When people respond, hand out abuse, ignore anything
which clearly looks credible, etc. Hand out more abuse. Change theory,
claiming people didn't understand. Hand out more abuse. Claim he was
right and others were wrong. Don't be surprised if the same theory is
recycled several times.

"Brian Reay" wrote in message
...
On 10/11/14 18:46, wrote:
Further proof, if any were needed, that a short antenna is a poor
radiator.
All the proof so far having acutal numbers has been that "a short antenna
is a poor radiator" is arm waving nonsense, gas bag, and all you have
presented so far is arm waving and no numbers.

It is worse than that, he has dismissed solid theory and tried to replace
it with his nonsense. Just as he has done in the rotating
magnetic thread. In fact, this is his normal mode of operation, he
has a long history of such quackery. The pattern is always the same.
Post some nonsense theory, often dressed up as being something that
has troubled him or he has been studying. The theories are often rambling
nonsense- suggesting any studying has been limited to a 'scan'
of a few key terms. When people respond, hand out abuse, ignore anything
which clearly looks credible, etc. Hand out more abuse. Change theory,
claiming people didn't understand. Hand out more abuse. Claim he was right
and others were wrong. Don't be surprised if the same theory is recycled
several times.

Once again, Brian, you jump in with your childish remarks and chanting
your false mantra.

Why do you behave like that?

Why always shout out your childish interjections?

Why not contribute to the technical discussion?

FYI, it was jimp who originated the abuse by his pejorative use of, "gas
bag",
but I doubt that the truth of that will suit your own need to want to shout
out
your own abuse.

I have not dismissed any theory. Out your money where your (big) mouth is,
and cite your reference.

I do not have a history of quackery, unlike youwith your assertion that
reversing
the direction od a rotating vector makes it reduce in suze, or more
recently, claiming that
Maxwell's equations for static fields have no non-zero differential terms,
or that
Maxwell's Equations refer only to EM propagation and not to the whole of
electrical
phenomenon. (Perhaps it is no surprise that you do an M6CIR and reort to
bluster
to mask your own technical ineptitude?)

I have never changed any theory; I strongly suspect that your problem is
that you yourself
are the one who only does a quick scan, jumps to some irrelevant conclusion,
and then
dives in with your own abuse; abuse that you seek to lay at others' doors.
For example,
your recent faux pas when I was discussing what leads to a standing wave
and you jumping
in with what is extant AFTER that standing wave has been set up.

Physician, heal thyself.