John S wrote in :

On 11/6/2014 11:33 AM, gareth wrote:
"John S" wrote in message
...
So, it appears that doubling the length of a short antenna captures about
3.6 times the signal.

And, therefore, by the reciprocity characteristic, the short antenna is
an inefficient radiator?

No, not at all. If the kind of reciprocity to which you refer were true,
then the receiving antenna would capture ALL the power radiated. That
obviously cannot be, so I think your idea of reciprocity may be a bit
flawed.


Jim said something the other day that made it clearest for me. He said (of
reciprocity, and not verbatim) that if some field arriving at an antenna
created some electrical signal at its feed point, then recreating that signal
would recreate that field at the antenna itself. My interpretation of that is
that while a receiving antenna, made bigger, captures more energy from a
diverging field from another source, this cannot be equated with transmission
where the whole energy source is transmitted from the antenna regardless of
size if impedance matching is good.

"FranK Turner-Smith G3VKI" wrote in
:

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.

I think your arms would start to ache quite quickly.


Just a tad...

Why would waving a magnet, at ANY speed, do it? I never heard of such. Got to
be a stationary conductor involved too, somewhere very nearby. The speed
would have far less to do with anything than the matching of kinetic energy
into the conductor, and the matching of that to whatever part of that
conductor is an antenna.

A magnet moving on its own reminds me of the question 'what is the sound of
one hand clapping?'

"gareth" wrote in message

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.


If it were true, then you'd be able to make a steel teaspoon stick to a
transmitting antenna made of copper as if that copper were a magnet. I don't
think that will happen.

Brian Reay wrote in
:

Why would waving a magnet, at ANY speed, do it? I never heard of such.
Got to be a stationary conductor involved too, somewhere very nearby.
The speed would have far less to do with anything than the matching of
kinetic energy into the conductor, and the matching of that to whatever
part of that conductor is an antenna.

Not a moving conductor, a changing electric field.


I mentioned stationary conductor, but my example was not rigorous..

He also seems to think that it is frequency which determines if it is an
EM wave, why else the
comment re fast enough. You can have a ELF radio wave, I know of
amateurs with NoVs to operate
around 9kHz.


Exactly so. That's what I was gettign at, that speed in itself means nothing,
it only becomes important when calculations need a frequency.


A magnet moving on its own reminds me of the question 'what is the
sound of one hand clapping?'

An apt comment.

Brian Reay wrote in news:835469977437141262.223254no.sp-
:

I think your arms would start to ache quite quickly.

I wonder what he would expect if he waved a battery about.


I'd expect muscle crapms, and if persistent, arthritis.

On Sat, 08 Nov 2014 06:41:10 -0600, Lostgallifreyan wrote:

An apt comment.



And somewhat too deep for this conversation :-)



--
M0WYM

"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

He also seems to think that it is frequency which determines if it is an
EM
wave, why else the
comment re fast enough.

Once again you misunderstand, and knowing you, it is a deliberate
misunderstanding
to give you the chance to be abusive. As to fast enough, see the comment
above re
no longer bing a short antenna.

A magnet moving on its own reminds me of the question 'what is the sound
of
one hand clapping?'
An apt comment.

Two ignoramuses do not make for a knowledgeable person.

"Brian Reay" wrote in message
...

I wonder what he would expect if he waved a battery about.

I expect that you would use it as an excuse to heap abuse in my direction.

On Sat, 08 Nov 2014 17:46:57 +0000, gareth wrote:


Two ignoramuses do not make for a knowledgeable person.

Neither does one really fat ignoramus, so it seems.

In rec.radio.amateur.antenna 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

Babbling nonsense, gas bag, and if you actually understood Maxwell you
would know why.

He also seems to think that it is frequency which determines if it is an
EM
wave, why else the
comment re fast enough.

Once again you misunderstand, and knowing you, it is a deliberate
misunderstanding
to give you the chance to be abusive. As to fast enough, see the comment
above re
no longer bing a short antenna.

Yet more babbling nonsense, gas bag.

A permenant magnet is NOT an antenna of any sort.


--
Jim Pennino