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Wimpie[_2_] · November 10th 14, 12:44 PM posted to rec.radio.amateur.antenna

El 10-11-14 3:51, rickman escribió:
On 11/9/2014 4:09 PM, Wimpie 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?

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.

I don't follow this at all. I'm not familiar with the principle of
reciprocity and so can't say if you are applying it correctly.

Just do a search on reciprocity in electronic systems, it isn't
difficult.

But consider this. If the rotating magnet were sending out EM waves,
it would require energy to do that. But a rotating magnet will rotate
indefinitely bar other sources of friction. So clearly it is not
emanating EM waves. An example is a magnet suspended over a
superconductor. It can be set spinning and will not stop for a long time.

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.

On an astronomical scale things are different.

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

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