wrote:
Cecil Moore wrote:
On my diagram, the coax is always connected
at A and B so *nothing has changed*. I just don't see
any reason for the common mode current at 'X' to be
exactly the same as the common mode current at 'B'.
Do you?

No, but no one said that except you.
What I said was:

Sorry, that's not what you said. What you said was that there is
as much common mode current flowing down the feedline (at point B)
as is flowing into the half-wave end-fed section of the antenna
(at point X).

+--A--------X-------------------
|
+--B--------Y

The half-wave end-fed antenna starts at point X. The feedline is
at point B. Here's what you said:

wrote:
1.) You have a half-wave end-fed antenna. There has to be as much
common mode current leaving the end of that point and flowing down the
feedline as there is flowing out onto the antenna at that point. There
isn't any exception to this rule.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:

The half-wave end-fed antenna starts at point X. The feedline is
at point B. Here's what you said:

wrote:
1.) You have a half-wave end-fed antenna. There has to be as much
common mode current leaving the end of that point and flowing down the
feedline as there is flowing out onto the antenna at that point. There
isn't any exception to this rule.

The STUB is a balanced transmission line. If you quoted the entire post
everyone would see what I meant.

Your constant little games of pulling things from context just waste
time and ruin the purpose of technical forums. You really should quit
that, and try to use the forums for education.

73 Tom

wrote:
Cecil Moore wrote:
The half-wave end-fed antenna starts at point X. The feedline is
at point B. Here's what you said:

wrote:
1.) You have a half-wave end-fed antenna. There has to be as much
common mode current leaving the end of that point and flowing down the
feedline as there is flowing out onto the antenna at that point. There
isn't any exception to this rule.

The STUB is a balanced transmission line. If you quoted the entire post
everyone would see what I meant.

That is a complete quote of your item number 1. What you said is
self explanatory. You said the current flowing onto the antenna
is equal to the current flowing down the feedline. You were wrong.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
That is a complete quote of your item number 1. What you said is
self explanatory. You said the current flowing onto the antenna
is equal to the current flowing down the feedline. You were wrong.

Cecil, rather than help people with questions and give them good
helpful answers you seem to just want to turn it into a peeing contest.
Even if you have to drop sentences to make it appear someone else is
wrong.

Why do you do that??? Don't you think it is more important to help the
guy asking the question than to play Cecil games??

Actually here is everything I said in CONTEXT. Tell me what is wrong
in the entire CONTEXT of what I said.

From: - view profile
Date: Thurs, Jul 6 2006 8:56 pm
Email:
Groups: rec.radio.amateur.antenna
wrote:
Tom, I didn't know that the feedline decoupling issues with J-poles
were so bad.

I'd be interested in more information about why it's such an issue.
Would a sleeve stub work better than an open wire stub? It's certainly
stupid to make the feedline MORE of an issue.



Look at what the J-pole really is.

1.) You have a half-wave end-fed antenna. There has to be as much
common mode current leaving the end of that point and flowing down the
feedline as there is flowing out onto the antenna at that point. There
isn't any exception to this rule.


2.) While that current may be small with a perfect half wave, it is
never zero. It gets worse fast of the antenna is not 1/2 wl long
electrically, or if it is thick.


3.) Now you have a 1/4 wl stub feeding that half-wave on the end. If
you perfectly floated that 1/4 wl stub, common mode current in the stub

would DECREASE as you move away from the feedpoint. But if you ground
the 1/4 wl stub, current common mode INCREASES as you move away from
the stub. This is why end-fed Zepps and J-poles model very good when a
perfect ground independent current source is used to feed them.
Unfortunately we can't do a perfect ground independent feedpoint in the

real world, so depending on the CM impedance the amount of pattern
distortion will be all over the place.


This is why Zepps, antennas that are really just the same as a J-pole,
are notorious for RF in the shack. The lack of feedlines in models are
why people who do not include the feeder or feedline matching device to

the 1/4 wl closed stub conclude they aren't so bad.


Why would anyone go through all that bother to complicate the feed
system in a Yagi is beyond me, when there are a half dozen easy
solutions that were mentioned here.


73 Tom

end of quote

So you see, you mislead people on purpose Cecil. Shame on you.

wrote:
Cecil, rather than help people with questions and give them good
helpful answers you seem to just want to turn it into a peeing contest.
Even if you have to drop sentences to make it appear someone else is
wrong.

Pot: Kettle, Kettle: Pot.

This was a deliberate dose of your own medicine. When you
stop the deliberate obfuscation of my postings, the problem
will cease to exist.

Why do you do that??? Don't you think it is more important to help the
guy asking the question than to play Cecil games??

You are the one who taught me to play those silly games, Tom.
Just as soon as you abandon your unethical methods of quoting,
I will stop mirroring your actions back at you. You have even
reverse-ordered the dates of my postings to make them appear
to mean the opposite of what they originally meant.

I know a few technical types who could be contributing to
this newsgroup but are afraid of attack from your junk yard dog
style. Your strategy seems to be to attack everyone who disagrees
with you and try to drive them off the newsgroup.

One of the QRZ moderators advised me to stop arguing with you
because "W8JI is never wrong, even when he is completely wrong".
He made me promise not to reveal his identity. Another individual
regularly sends me technical information to use against your
irrational arguments but makes me promise to keep his identity a
secret lest he suffer one of your attacks. You have intimidated
a lot of people with your attack dog style. One wonders why, if
you are such a guru, you need to adopt such a style. How about
a kindler, gentler W8JI in the future?

I'm willing to agree to a truce which limits your and my postings
to technical information and logical arguments. Are you willing to
give up your ad hominem attacks and obfuscation of my postings?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
wrote:
Cecil, rather than help people with questions and give them good
helpful answers you seem to just want to turn it into a peeing contest.
Even if you have to drop sentences to make it appear someone else is
wrong.

Pot: Kettle, Kettle: Pot.

This was a deliberate dose of your own medicine. When you
stop the deliberate obfuscation of my postings, the problem
will cease to exist.

That's not true.

You interact with others through obfuscation and bullying. I just wish
you could control it a little bit becuase you do have useful things to
say. Sometimes people want answers to questions Cecil. The J-pole is a
good example where the focus should be on the antenna.

All of the models I've found on Cebik's site and nearly all of the
models elsewhere lack a ground or mast connection at the shorted
feed-stub junction, while most J-poles have that connection. They also
use a floating ground independent current source, which virtually no
J-poles have in the real world. I'd bet nearly all J-pole are
eventually fed by unbalanced feedlines or feedlines with finite common
mode.

The models, through pure accident or lack of basic understanding, use a
BEST case feed simulation that masks all of the problems a J-pole has
with common mode current.

No designer in his right mind would use such a lousy feed system to
feed a pattern sensitive design like a Yagi antenna, they are barely
acceptable as a omni-antenna.

73 Tom