On 6/9/2011 2:37 PM, Cecil Moore wrote:
On Jun 9, 10:30 am, John wrote:
I just highlight, and then right click the post, of mine, which is in
error. If using thunderbird (and I think you are), a menu will pop up,

I was previously using Thunderbird but AT&T dropped their news-server
function and I am now using Google Groups which apparently doesn't
allow a posting to be canceled.
--
73, Cecil, w5dxp.com

Give "Eternal September" a look-see.

John - KD5YI

On Jun 8, 11:06*pm, Camelot wrote:
Hello, I have some doubts about standing waves on antennas that I hope
you could clarify!
As far as I understood, in a generic transmission line where we want
only carry power from a source to a load, we need to cancel the
reflected wave by adapting the load with the impedance of the line.
The result of this operation is S11=S22=0 and VWWR=1 that means no
standing waves.
As far as I understood, in an antenna we want to also avoid standing
waves by having *VWWR=1 in order to avoid overloading problem to the
power stage...
From theory I know that the best radiating condition for an antenna is
when it resonates, that is, *when there is a standing wave… is that
correct? How this condition is compatible with a *VWWR=1 (no standing
waves) for a good antenna matching? Is there something that I’m not
catching?

Regards,

Camelot

Something else to think about that may help you understand:

Realize that if you connect a section of transmission line with one
impedance to a section with a different impedance, you will in general
have very different standing waves on the two sections. So, for
example, if you connect the output of a transmitter to a 50 ohm line
that goes for some distance, and that connects to a 250 ohm line
that's an even number of quarter waves long, and at the end of that
line there's a 50 ohm load, assuming the 250 ohm line is lossless, the
50 ohm line will see a 50 ohm load and have no standing wave. But the
250 ohm line has a 5:1 SWR.

Similarly, though the antenna conductors may have a large standing
wave on them, they may reflect a load to their input, their feedpoint,
that allows a low SWR on the feedline connected to that feedpoint.

You might think of the antenna as a "lossy transmission line," where
its loss is (mostly) radiation. You can then see another example
using just transmission lines...this time the 50 ohm line from the
transmitter connects to a piece of 75 ohm line. The 75 ohm line is
some even number of half-waves long, and it happens to have 7dB of
loss -- maybe it's fairly small line, or is several wavelengths long.
(In this case, the loss is as heating in the conductors of the line,
not radiation as in the antenna.) At the far end, it's shorted, so
the SWR at the short is clearly infinite. But at the end connected to
the 50 ohm line, because of the loss in the 75 ohm line, the 50 ohm
line sees a 50 ohm load, and the SWR on the 50 ohm line is 1:1. Note
that along the 75 ohm line, the SWR went from infinity at the shorted
far end, to 1.5:1 where the line connects to the 50 ohm line.

Cheers,
Tom

On Jun 9, 12:37*pm, Cecil Moore wrote:
On Jun 9, 10:30*am, John Smith wrote:

I just highlight, and then right click the post, of mine, which is in
error. If using thunderbird (and I think you are), a menu will pop up,

I was previously using Thunderbird but AT&T dropped their news-server
function and I am now using Google Groups which apparently doesn't
allow a posting to be canceled.
--
73, Cecil, w5dxp.com

Try the "More options", to the right of your name at the top of the
displayed message. There's a "remove" option in there, that doesn't
appear if you're not the author of the message. I assume that will
delete it, though I don't actually have experience doing that, at
least not recently.

Cheers,
Tom

On 6/9/2011 4:13 PM, K7ITM wrote:
On Jun 8, 11:06 pm, wrote:
Hello, I have some doubts about standing waves on antennas that I hope
you could clarify!
As far as I understood, in a generic transmission line where we want
only carry power from a source to a load, we need to cancel the
reflected wave by adapting the load with the impedance of the line.
The result of this operation is S11=S22=0 and VWWR=1 that means no
standing waves.
As far as I understood, in an antenna we want to also avoid standing
waves by having VWWR=1 in order to avoid overloading problem to the
power stage...
From theory I know that the best radiating condition for an antenna is
when it resonates, that is, when there is a standing wave… is that
correct? How this condition is compatible with a VWWR=1 (no standing
waves) for a good antenna matching? Is there something that I’m not
catching?

Regards,

Camelot

Something else to think about that may help you understand:

Realize that if you connect a section of transmission line with one
impedance to a section with a different impedance, you will in general
have very different standing waves on the two sections. So, for
example, if you connect the output of a transmitter to a 50 ohm line
that goes for some distance, and that connects to a 250 ohm line
that's an even number of quarter waves long, and at the end of that
line there's a 50 ohm load, assuming the 250 ohm line is lossless, the
50 ohm line will see a 50 ohm load and have no standing wave. But the
250 ohm line has a 5:1 SWR.

Similarly, though the antenna conductors may have a large standing
wave on them, they may reflect a load to their input, their feedpoint,
that allows a low SWR on the feedline connected to that feedpoint.

You might think of the antenna as a "lossy transmission line," where
its loss is (mostly) radiation. You can then see another example
using just transmission lines...this time the 50 ohm line from the
transmitter connects to a piece of 75 ohm line. The 75 ohm line is
some even number of half-waves long, and it happens to have 7dB of
loss -- maybe it's fairly small line, or is several wavelengths long.
(In this case, the loss is as heating in the conductors of the line,
not radiation as in the antenna.) At the far end, it's shorted, so
the SWR at the short is clearly infinite. But at the end connected to
the 50 ohm line, because of the loss in the 75 ohm line, the 50 ohm
line sees a 50 ohm load, and the SWR on the 50 ohm line is 1:1. Note
that along the 75 ohm line, the SWR went from infinity at the shorted
far end, to 1.5:1 where the line connects to the 50 ohm line.

Cheers,
Tom

Well done, Tom. Kudos.

73,
John - KD5YI

On Wed, 8 Jun 2011 23:06:00 -0700 (PDT), Camelot
wrote:

From theory I know that the best radiating condition for an antenna is
when it resonates, that is, when there is a standing wave… is that
correct?

No.

73's
Richard Clark, KB7QHC

On 6/9/2011 12:37 PM, Cecil Moore wrote:
On Jun 9, 10:30 am, John wrote:
I just highlight, and then right click the post, of mine, which is in
error. If using thunderbird (and I think you are), a menu will pop up,

I was previously using Thunderbird but AT&T dropped their news-server
function and I am now using Google Groups which apparently doesn't
allow a posting to be canceled.
--
73, Cecil, w5dxp.com

You can get a free email account he

http://gmx.com/

You can then use that email acount to get a free post/read account he

http://eternal-september.org/RegisterNewsAccount.php

You will be back in business with tbird and an email that people can
spam from here to high heaven, without worry ...

Just in case you are interested ... good luck, either way.

--

Regards,
JS
“The Constitution is not an instrument for the government to restrain
the people, it’s an instrument for the people to restrain the
government.” -- Patrick Henry

On Thu, 09 Jun 2011 18:54:07 -0700, John Smith
wrote:

On 6/9/2011 12:37 PM, Cecil Moore wrote:
On Jun 9, 10:30 am, John wrote:
I just highlight, and then right click the post, of mine, which is in
error. If using thunderbird (and I think you are), a menu will pop up,

I was previously using Thunderbird but AT&T dropped their news-server
function and I am now using Google Groups which apparently doesn't
allow a posting to be canceled.
--
73, Cecil, w5dxp.com

You can get a free email account he

http://gmx.com/

You can then use that email acount to get a free post/read account he

http://eternal-september.org/RegisterNewsAccount.php

You will be back in business with tbird and an email that people can
spam from here to high heaven, without worry ...

Just in case you are interested ... good luck, either way.

If you don't want want to mess around registering for the news server
or getting a throw away address, you can use the free nntp.aioe.org.
Just plug it into TB or any newsreader and away you go. There are more
restrictions than eternal-september but if you have a life other than
Usenet they won't bother you...

(http://www.aioe.org/index.php?home)

On 6/9/2011 8:46 PM, AJL wrote:

...
If you don't want want to mess around registering for the news server
or getting a throw away address, you can use the free nntp.aioe.org.
Just plug it into TB or any newsreader and away you go. There are more
restrictions than eternal-september but if you have a life other than
Usenet they won't bother you...

(http://www.aioe.org/index.php?home)

True, the thing with aioe.org is that you don't need to create a
password and no need for a real email addy, even of the throwaway kind ...

This is great in an aid of making the world wide wiretap more difficult
to track/trace you, couple that up with a phony isp number, change the
volume id only hard drive now and then, and use mac makeup to switch the
mac no. on your nic now and then and it becomes even more difficult, use
another identity to make it appear as if you are really someone else and
you start getting a bit of security ...

Really, no one should be using their real isp for usenet anyway!
Everyone should be pretending like it's 1984, which it is!

--

Regards,
JS
“The Constitution is not an instrument for the government to restrain
the people, it’s an instrument for the people to restrain the
government.” -- Patrick Henry

Great! Thank you for your useful comments!

Camelot