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Old February 21st 16, 11:05 PM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....

Forgiving their ignorant use of the wrong plural, "antennas", this is a
brilliant site, at first sight ...

http://antenna-theory.com/


In particular, the following sub-page may teach the Yank rednecks
who abuse this NG a thing or two ...


http://www.antenna-theory.com/antennas/shortdipole.php



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Old February 21st 16, 11:29 PM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....



"gareth" wrote in message ...

Forgiving their ignorant use of the wrong plural, "antennas", this is a
brilliant site, at first sight ...


http://antenna-theory.com/



In particular, the following sub-page may teach the Yank rednecks
who abuse this NG a thing or two ...



http://www.antenna-theory.com/antennas/shortdipole.php


Good references, but I see nothing new in the second reference with regard
to short dipoles.

If you can get 100 watts into a one foot long HF dipole, it will be just as
efficient as a half wave dipole that also has 100 watts into it.

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Old February 22nd 16, 12:00 AM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....

Wayne wrote:

"gareth" wrote in message ...

Forgiving their ignorant use of the wrong plural, "antennas", this is a
brilliant site, at first sight ...


http://antenna-theory.com/



In particular, the following sub-page may teach the Yank rednecks
who abuse this NG a thing or two ...



http://www.antenna-theory.com/antennas/shortdipole.php


Good references, but I see nothing new in the second reference with regard
to short dipoles.

If you can get 100 watts into a one foot long HF dipole, it will be just as
efficient as a half wave dipole that also has 100 watts into it.


Agreed. It is a good summary. It confirms what many of us have said,
that there is nothing special about a small antenna that makes it
inefficient except that it has an inconvenient reactive impedance and a
low radiation resistance. Given a theoretical lossless matching network
(which would be impossible to realise in practice) the one in the
example could be 99% efficient, as the loss resistance of the actual
antenna is only about 1% of the radiation restistance.

If Gareth now agrees with this analysis we are now in the happy position
of all agreeing.

--

Roger Hayter
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Old February 22nd 16, 02:20 PM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....


"Wayne" wrote in message
...
If you can get 100 watts into a one foot long HF dipole, it will be just
as efficient as a half wave dipole that also has 100 watts into it.


But only on the very narrow band that your lossless matching covers.
If you want the bandwidth of an halfwave dipole you will need
a lot of one foot ones plus a lossless distribution filter.
Very far form "as efficient" IMHO
And on receive the things get worse :-)


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Old February 22nd 16, 04:03 PM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....

bilou wrote:

"Wayne" wrote in message
...
If you can get 100 watts into a one foot long HF dipole, it will be just
as efficient as a half wave dipole that also has 100 watts into it.


But only on the very narrow band that your lossless matching covers.
If you want the bandwidth of an halfwave dipole you will need
a lot of one foot ones plus a lossless distribution filter.
Very far form "as efficient" IMHO
And on receive the things get worse :-)


I don't think anyone disputes that it would be a hopeless antenna
*system*. The point being that the antenna itself is not particularly
inefficient in the technical sense, just very inconvenient to feed. And
that was the original point in dispute.



--

Roger Hayter


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Old February 22nd 16, 07:10 PM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....



"Roger Hayter" wrote in message
...

bilou wrote:

"Wayne" wrote in message
...
If you can get 100 watts into a one foot long HF dipole, it will be just
as efficient as a half wave dipole that also has 100 watts into it.


But only on the very narrow band that your lossless matching covers.
If you want the bandwidth of an halfwave dipole you will need
a lot of one foot ones plus a lossless distribution filter.
Very far form "as efficient" IMHO
And on receive the things get worse :-)


# I don't think anyone disputes that it would be a hopeless antenna
# *system*. The point being that the antenna itself is not particularly
# inefficient in the technical sense, just very inconvenient to feed. And
# that was the original point in dispute.

Dead on explanation. Some have insisted that inefficiencies result from
antenna size and not from matching challenges.

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Old February 24th 16, 01:19 AM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....

"Wayne" wrote

Dead on explanation. Some have insisted that inefficiencies
result from antenna size and not from matching challenges.

_______

Kindly note that the radiation efficiency of an antenna _system_ is related
to its radiation resistance compared to other resistive losses present in
that antenna system.

It is possible to perfectly match the impedance at the feedpoint of an
antenna system to the impedance of the transmission line connected there.
But that antenna system still can have very poor radiation efficiency at
that frequency.

An example of this is a Z-matched, but electrically short vertical monopole
driven against a poor r-f ground connection such as a few buried ground
rods. Most of the available transmitter power is dissipated in the r-f
ground resistance, rather than being usefully radiated as e-m waves.

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Old February 24th 16, 01:55 AM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....

Richard Fry wrote:

"Wayne" wrote

Dead on explanation. Some have insisted that inefficiencies
result from antenna size and not from matching challenges.

_______

Kindly note that the radiation efficiency of an antenna _system_ is related
to its radiation resistance compared to other resistive losses present in
that antenna system.

It is possible to perfectly match the impedance at the feedpoint of an
antenna system to the impedance of the transmission line connected there.
But that antenna system still can have very poor radiation efficiency at
that frequency.

An example of this is a Z-matched, but electrically short vertical monopole
driven against a poor r-f ground connection such as a few buried ground
rods. Most of the available transmitter power is dissipated in the r-f
ground resistance, rather than being usefully radiated as e-m waves.


That is true. But the statement you were responding to was made in
response to a specific example where the RF loss resistance was much
smaller than the 0.49.ohm radation resistance. And the whole
discussion arose from the suggestion that short antennas are
*necessarily* inefficient because they cannot radiate without loss.
Your example is a good one of a system with a large loss resistance
which needs a higher radiation resistance monopole to feed the
combination efficiently in series. It is a perfectly good example, but
shows nothing about the intriinsic radiation efficiency of a short
antenna, just about its practical usefulness in a certain situations.


--

Roger Hayter
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Old February 24th 16, 01:56 AM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....

In rec.radio.amateur.antenna Richard Fry wrote:
"Wayne" wrote

Dead on explanation. Some have insisted that inefficiencies
result from antenna size and not from matching challenges.

_______

Kindly note that the radiation efficiency of an antenna _system_ is related
to its radiation resistance compared to other resistive losses present in
that antenna system.

It is possible to perfectly match the impedance at the feedpoint of an
antenna system to the impedance of the transmission line connected there.
But that antenna system still can have very poor radiation efficiency at
that frequency.

An example of this is a Z-matched, but electrically short vertical monopole
driven against a poor r-f ground connection such as a few buried ground
rods. Most of the available transmitter power is dissipated in the r-f
ground resistance, rather than being usefully radiated as e-m waves.


And the poor ground is not part of the antenna system?



--
Jim Pennino
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Old February 28th 16, 06:56 PM posted to rec.radio.amateur.antenna,uk.radio.amateur
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Default Everything you want to know about antennae ....



"Richard Fry" wrote in message ...

"Wayne" wrote

Dead on explanation. Some have insisted that inefficiencies
result from antenna size and not from matching challenges.

_______

Kindly note that the radiation efficiency of an antenna _system_ is related
to its radiation resistance compared to other resistive losses present in
that antenna system.


It is possible to perfectly match the impedance at the feedpoint of an
antenna system to the impedance of the transmission line connected there.
But that antenna system still can have very poor radiation efficiency at
that frequency.


An example of this is a Z-matched, but electrically short vertical monopole
driven against a poor r-f ground connection such as a few buried ground
rods. Most of the available transmitter power is dissipated in the r-f
ground resistance, rather than being usefully radiated as e-m waves.


Duly noted, but the technical point I addressed was a bit different from the
antenna system you describe.

There has previously on the newsgroup been a claim that shortness makes
inefficiency.
To that I say that if for example, 100 watts is fed to a resonant HF dipole,
and 100 watts is fed to a 1 foot long dipole, both radiate 100 watts.
Different patterns, but the power radiated is the same, if you manage to
successfully get the power to the antenna.




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