"rickman" wrote in message
...
On 9/11/2015 1:48 PM, gareth wrote:
"rickman" wrote in message
...

There is no contradiction there. Current is not power. Power is
voltage
times current. Since the impedance of a short antenna is not the same
as
the impedance of a larger antenna, it makes perfect sense that the
current
for a given power level will not be the same.

Feed 1kW into your 472kHz antenna and get only 1W erp, most of
the high current driving the ohmic resistance and not the radiation
resistance

You have had this discussion with many others here before. What is your
point?

The point I was making was a courteous reply to you.

On 9/11/2015 10:58 PM, gareth wrote:
"rickman" wrote in message
...
On 9/11/2015 1:48 PM, gareth wrote:
"rickman" wrote in message
...

There is no contradiction there. Current is not power. Power is
voltage
times current. Since the impedance of a short antenna is not the same
as
the impedance of a larger antenna, it makes perfect sense that the
current
for a given power level will not be the same.

Feed 1kW into your 472kHz antenna and get only 1W erp, most of
the high current driving the ohmic resistance and not the radiation
resistance

You have had this discussion with many others here before. What is your
point?

The point I was making was a courteous reply to you.

I'm talking about the technical point. Your reply doesn't have much
technical merit about the question you were originally asking. You
snipped the part I was replying to.

Therefore, to achieve the same radiated power from a short antenna, the
current
in the antenna has to be higher.

My point is that the current is not relevant in the theoretical case.
The ohmic losses you are talking about have to do with the construction
of the antenna, not the geometry. Make an antenna from a super
conductor with no ohmic losses and you will see the same power radiate
from both a short or a long antenna given the same power input to the
antenna.

There is my courteous reply to you, and fully on topic. Can you give a
valid technical reply about that?

--

Rick

"rickman" wrote in message
...

My point is that the current is not relevant in the theoretical case. The
ohmic losses you are talking about have to do with the construction of the
antenna, not the geometry. Make an antenna from a super conductor with no
ohmic losses and you will see the same power radiate from both a short or
a long antenna given the same power input to the antenna.

No you won't, for not only will your feeder be matched to your antenna, but
the antenna will be matched to the feeder, and the stored energy that is not
radiated because
of the shorted antenna will go back down the feeder.

On 9/12/2015 3:10 PM, gareth wrote:
"rickman" wrote in message
...

My point is that the current is not relevant in the theoretical case. The
ohmic losses you are talking about have to do with the construction of the
antenna, not the geometry. Make an antenna from a super conductor with no
ohmic losses and you will see the same power radiate from both a short or
a long antenna given the same power input to the antenna.

No you won't, for not only will your feeder be matched to your antenna, but
the antenna will be matched to the feeder, and the stored energy that is not
radiated because
of the shorted antenna will go back down the feeder.

Uh, if they are matched, there won't be any reflection energy. It all
gets radiated. You keep getting hung up on the specifics of an
installation when you appear to be asking a question about theory. Yes,
short antenna are not used in practice because they are hard to match to
a feedline and transmitter. But your original question as posited was
about the inherent differences in radiated power given an amount of
power input to the antenna. Quit mixing the theory and the practice or
clearly state which one you are talking about.

Here, this question you asked originally...

What is the nature of free space such that it requires antennae to be at
least 1/4 wave
before accepting radiation efficiently?

Nothing here says anything about the ohmic resistance of the antenna or
the impedance of the feedline. You seem to be asking about how the
power leaves the antenna and radiates as an EM wave.

--

Rick

"rickman" wrote in message
...
Uh, if they are matched, there won't be any reflection energy.

Untrue, because you match the inout impedance but not the radiation
resistance,
which in the case of a dipole are largely the same, so, yes, in a dipole it
does all get radiated.

On 9/12/2015 5:33 PM, Brian Morrison wrote:
On Sat, 12 Sep 2015 22:17:27 +0100
"gareth" wrote:

"rickman" wrote in message
...
Uh, if they are matched, there won't be any reflection energy.

Untrue, because you match the inout impedance but not the radiation
resistance,
which in the case of a dipole are largely the same, so, yes, in a dipole it
does all get radiated.



If it doesn't get radiated with a matched antenna that has a small
radiation resistance then that remaining energy is converted into heat
in the antenna/matching network, not reflected back to the Tx.

Picture that with ideal components and then tell me what happens. Or
better yet, since we are talking about antenna geometry and not feed
lines and matching networks, imagine *no* feed line, just a signal
generator with a dipole attached directly to the output. The output
impedance of the generator exactly matches the input impedance of the
antenna in each case. The power measured going into the antenna in each
case is 100 W. Will the emitted field be the same?

--

Rick

"rickman" wrote in message ...

On 9/12/2015 5:33 PM, Brian Morrison wrote:
On Sat, 12 Sep 2015 22:17:27 +0100
"gareth" wrote:

"rickman" wrote in message
...
Uh, if they are matched, there won't be any reflection energy.

Untrue, because you match the inout impedance but not the radiation
resistance,
which in the case of a dipole are largely the same, so, yes, in a dipole
it
does all get radiated.



If it doesn't get radiated with a matched antenna that has a small
radiation resistance then that remaining energy is converted into heat
in the antenna/matching network, not reflected back to the Tx.

# Picture that with ideal components and then tell me what happens. Or
# better yet, since we are talking about antenna geometry and not feed
# lines and matching networks, imagine *no* feed line, just a signal
# generator with a dipole attached directly to the output. The output
# impedance of the generator exactly matches the input impedance of the
# antenna in each case. The power measured going into the antenna in each
# case is 100 W. Will the emitted field be the same?

I'm with you. For a valid comparison of the radiation of two antennas, they
both have to have the same power radiated to start with.
If one has power reflected/consumed by heat or whatever, then simply crank
up the power for that antenna until they both radiate the same power.

Let's consider an isotropic antenna (that's about the limit of "shortness")
compared with whatever bigger antenna.

At distance D, the isotropic antenna will have all its power spread over a
spherical surface of radius D.

As I understand Gareth's assertion, at every position on the point source
sphere, the field strength would be lower than for a bigger antenna
replacing the point source.
I doubt that is true.

On Saturday, September 12, 2015 at 6:52:44 PM UTC-5, Wayne wrote:

As I understand Gareth's assertion, at every position on the point source
sphere, the field strength would be lower than for a bigger antenna
replacing the point source.
I doubt that is true.

He's trying to blame the poor old radiator, "free space", or the "Aether"
for rig to feed line to radiator matching losses.

My reason to even join this circus is to bring to his attention that
his opening statement is totally false.

The Lumeniferous Aether... The story of Art Unwin's long lost cousin.

chortle..

wrote:
On Saturday, September 12, 2015 at 6:52:44 PM UTC-5, Wayne wrote:

As I understand Gareth's assertion, at every position on the point source
sphere, the field strength would be lower than for a bigger antenna
replacing the point source.
I doubt that is true.

He's trying to blame the poor old radiator, "free space", or the "Aether"
for rig to feed line to radiator matching losses.

My reason to even join this circus is to bring to his attention that
his opening statement is totally false.

The Lumeniferous Aether... The story of Art Unwin's long lost cousin.

chortle..

It seems quite evident that Gareth's mental state has recently deteriorated
even further than its usual squalid depths.

--
STC // M0TEY // twitter.com/ukradioamateur

Stephen Thomas Cole wrote:

wrote:
On Saturday, September 12, 2015 at 6:52:44 PM UTC-5, Wayne wrote:

As I understand Gareth's assertion, at every position on the point source
sphere, the field strength would be lower than for a bigger antenna
replacing the point source.
I doubt that is true.

He's trying to blame the poor old radiator, "free space", or the "Aether"
for rig to feed line to radiator matching losses.

My reason to even join this circus is to bring to his attention that
his opening statement is totally false.

The Lumeniferous Aether... The story of Art Unwin's long lost cousin.

chortle..

It seems quite evident that Gareth's mental state has recently deteriorated
even further than its usual squalid depths.

Have you nothing to say on the subject of aerials? You could at least
correct the spelling of "luminiferous" if you have nothing else useful
to say.

--
Roger Hayter