A short 160M antenna
 

Jeff wrote in :

On 08/11/2014 17:46, gareth wrote:
"Brian Reay" wrote in message
...

He isn't the first fool to think he could generate an EM wave breaking
Maxwell's laws.

You continue to be the one who originates ths abuse that you seek to
lay at others'
door, and you continue to misunderstand Maxwell.

The changing magnetic field cause by rotating a magent at such a speed
that it would cease to be a short antennae will create a changing
electric field, as described by Maxwell


For once have to agree with Gareth, a rotating magnet will cause EM
radiation.

Jeff



*silently munches popcorn, waits for picture to start*

A short 160M antenna
 

Jeff wrote in :

For once have to agree with Gareth, a rotating magnet will cause EM
radiation.


Ok, maybe so. Is this right...? Suppose a wire is part of a closed circuit,
that magnet would certainly induce current. Now, if that wire were NOT
closed, but in the form of some antenna, then at an appropriate frequency, in
the part of an antenna that normally sees current (at the feedpoint end), you
would see a current, thus all the other attributes of an antenna subject to
an electromagnetic field would also exist? IF (I'm not stating, just trying
to follow a thought based on what you said), IF this is so, then it would
mean the EM wave existed with or without the wire, purely because the magnet
was spinning.

Alternatively, does it just mean that an alternative magnetic field near an
antenna feedpoint is as capable of inducing a signal out of the antenna as an
electromagnetic wave is?

Maybe I should go back to my popcorn. I may not even understand what I see,
but I want to watch.

A short 160M antenna
 

"Sn!pe" wrote in message
o.uk...

What produces the electric component of the EM field?

The changing magnetic field.

Of course, it should go withour saying that the axis of spin must
be between the N and S poles, and not along the axis of the magnet,
in case of confusion thereto.

A short 160M antenna
 

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

"Sn!pe" wrote in message
o.uk...

What produces the electric component of the EM field?

The changing magnetic field.

Of course, it should go withour saying that the axis of spin must
be between the N and S poles, and not along the axis of the magnet,
in case of confusion thereto.

I don't understand. Is it not the case that the electric component of
the EM field arises from a voltage difference? How does that voltage
difference arise, please?

I suggest that you go back to an earlier level and think about the dynamo,
alternator and transformer, where a changing magnetic field produces
an electric field, for it is the same principle.

It is unfortunate that matters of electricity are very difficult to
understand
in full, so we are presented with a series of models (usually starting off
with the increasing pressure as the depth of water in a bucket is increased)
none of which are absolutely correct, but all of which get us over a hurdle
of understanding until along comes the next model.

And the biggest partial model that leads to much understanding is that
electricity is all about pos and neg charges whereas in fact it is
all about the EM fields!

A short 160M antenna
 

"Sn!pe" wrote in message
. uk...
Do not dynamos, alternators and transformers rely on currents induced
into *conductors* by changing magnetic fields? Please see 'Faraday's
Law of Induction' regarding the current induced into a conductor.

https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction


Actually it is explained in the opening remarks of that article where it
says that an EMF is produced.

A short 160M antenna
 

"Sn!pe" wrote in message
. uk...
Where is the conductor in your 'rotating magnet' suggestion? Is it not
the case that the current gives rise to the potential difference from
which the eletric field arises? It is the current that is directly
responsible for the magnetic component, of course.

I attempted a partial explanation of your question in the following
paragraph ...

And the biggest partial model that leads to much MISunderstanding is that
electricity is all about pos and neg charges whereas in fact it is
all about the EM fields!


Perhaps I'm just being dense,

I doubt that very much.

but I still don't see how the electric
component of the propagating EM field arises in your scenario. I have
to admit, though, that it's probably 50 years since I last looked at
this stuff in (I think) the ARRL Handbook, perhaps my memory is at
fault.

Well, it is 42 years since I studied all that stuff*****, admittedly in the
3rd year
of an electronics course at University, and perhaps therein lies the problem
for many people, for unless you have studied differential vector fields then
you won't have the backgrund for Maxwell's Equations.

By saying that, I do not mean to be condescending and am always willing
to help others. Maxwell's equations are the starting point for a real
understanding
of all matters electrical.

***** apart frm a bit of revision a few years ago to understand the claims
made by the Crossed Field Antenna idea.

A short 160M antenna
 

On 09/11/14 13:01, Sn!pe wrote:
gareth wrote:

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

"Sn!pe" wrote in message
o.uk...

What produces the electric component of the EM field?


The changing magnetic field.

Of course, it should go withour saying that the axis of spin must
be between the N and S poles, and not along the axis of the magnet,
in case of confusion thereto.


I don't understand. Is it not the case that the electric component of
the EM field arises from a voltage difference? How does that voltage
difference arise, please?


I suggest that you go back to an earlier level and think about the dynamo,
alternator and transformer, where a changing magnetic field produces
an electric field, for it is the same principle.


Do not dynamos, alternators and transformers rely on currents induced
into *conductors* by changing magnetic fields? Please see 'Faraday's
Law of Induction' regarding the current induced into a conductor.

https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction

Where is the conductor in your 'rotating magnet' suggestion? Is it not
the case that the current gives rise to the potential difference from
which the eletric field arises? It is the current that is directly
responsible for the magnetic component, of course.


It is unfortunate that matters of electricity are very difficult to
understand
in full, so we are presented with a series of models (usually starting off
with the increasing pressure as the depth of water in a bucket is increased)
none of which are absolutely correct, but all of which get us over a hurdle
of understanding until along comes the next model.

And the biggest partial model that leads to much understanding is that
electricity is all about pos and neg charges whereas in fact it is
all about the EM fields!


I agree that "It is unfortunate that matters of electricity are very
difficult to understand in full".

Perhaps I'm just being dense, but I still don't see how the electric
component of the propagating EM field arises in your scenario. I have
to admit, though, that it's probably 50 years since I last looked at
this stuff in (I think) the ARRL Handbook, perhaps my memory is at
fault.



You are not 'being dense', you are perfectly correct.

Waving a magnet will not generate an EM wave, it won't even induce a
current unless there is a conductor to hand.

Likewise, waving a battery around, won't generate an EM wave either.

Maxwell's equations come as a 'set' to generate an EM wave, you can't
start with just one. That was one of the flaws in the Cross Field
Antenna theory-or the original one, it varied as it was challenged. It
had other flaws, eg the idea that the Poynting vector was some 'extra'
physical phenomenon which could be 'synthesised', rather than just a
mathematical vector representation of the power in the E and M fields.

As I pointed out in a previous post, the differential term is zero in
the absence of one of the fields so the equations have no, non-trivial,
solutions.

As I recall, this is one of the standard things you are taught when you
attend a lecture on Maxwell's Equations. Perhaps someone missed a
lecture (or more),has lost some crucial pages from his notes,or hasn't
got a clue.

Like all equations, if you apply them correctly, Maxwell's equations do
work. However, if you can't understand them, you will mislead yourself.

A short 160M antenna
 

Lostgallifreyan wrote in
:

IF (I'm not stating, just trying
to follow a thought based on what you said), IF this is so, then it
would mean the EM wave existed with or without the wire, purely because
the magnet was spinning.


Ok, scratch that! My own speculation is plain wrong, surely. The earlier
point in myearlier post MAY be true, but if so, only because the presence of
a nearby antenna feedpoint means that a current carrying wire is actually
present. All this, assuming that you can use the current carrying portion of
some antenna as if it were a winding in a dynamo, given a magnetic field
varying at a rate appropriate for said antenna. Even if this IS possible, it
isn't the same as doing an EM wave with no wire at all. That would be magic,
no?

A short 160M antenna
 

"Brian Reay" wrote in message
...
Waving a magnet will not generate an EM wave, it won't even induce a
current unless there is a conductor to hand.

From Maxwell, del cross E = -dB/dt

Maxwell's equations come as a 'set' to generate an EM wave,

I regret that you have only part of the story, for Maxwell's Equations
describe _ALL_ electrical phenomena.

you can't
start with just one.

I regret that you are not correct there.

As I pointed out in a previous post, the differential term is zero in the
absence of one of the fields so the equations have no, non-trivial,
solutions.

That was not what you said before, and now you are attempting to change
history
in order to save face. You said that for static fields there were no
non-zero differential
results and you poured scorn not only on my background, but also on Essex
University where I studied.

As I recall, this is one of the standard things you are taught when you
attend a lecture on Maxwell's Equations. Perhaps someone missed a lecture
(or more),has lost some crucial pages from his notes,or hasn't got a
clue.

Well, Brian, M3OSN,Old Chap, you accuse me of making comments as
an excuse to originate abuse, but, once again, it is only you who displays
the
fault that you allege.

Like all equations, if you apply them correctly, Maxwell's equations do
work. However, if you can't understand them, you will mislead yourself.

Do you mean those who ahve not grasped that they apply to _ALL_ electrical
phenomena?

A short 160M antenna
 

"gareth" wrote in message
...
"Brian Reay" wrote in message
...
As I pointed out in a previous post, the differential term is zero in the
absence of one of the fields so the equations have no, non-trivial,
solutions.

That was not what you said before, and now you are attempting to change
history
in order to save face. You said that for static fields there were no
non-zero differential
results and you poured scorn not only on my background, but also on Essex
University where I studied.

And here is the evidence of your attempt to rewrite history in order to save
face,
coupled once again with your uncontrollable urge to make nasty comments
in passing (Why do you behave like that?) ...

-----ooooo-----

"Brian Reay" wrote in message
...

Of course, regardless of the day of the week, Maxwell is much good for a
static field. (Differential = 0).
The appalling lack of mathematical ability shown by some who claim degrees
in engineering really makes you wonder at times. Especially as that would
have been in a maths
qualification required for any decent Uni. entry.