"David G. Nagel" wrote in message
...
Jerry Martes wrote:

"Cecil Moore" wrote in message
...

dansawyeror wrote:

Below is a link to a site that claims to model coax radiation from a
dipole.

http://www.smeter.net/feeding/feedpowr.php

Please note that the third wire to ground creates the unbalance
that causes feedline radiation. You seem to be confusing cause
and effect. The cause of the feedline radiation is the existence
of that third wire, not SWR. All it proves is that feedline
radiation is caused by that third wire path which unbalances
the source currents.
--
73, Cecil http://www.qsl.net/w5dxp


Cecil

How wrong would it be to say that the *coax* part of the line doesnt
radiate at all?
I see this as a situation where the *outer shield* of a transmission
line is conducting current that radiates.
It seems that a "balanced" antenna that is comprised of a single
conductor and a L shaped conductor that includes the outer conductor of
the coax, could be fed with a balanced line for modeling.

Jerry
What I was taught is that in a properly installed antenna system the coax
will not radiate. If the antenna is not properly matched to the coax you
get current flow along the outside of the coax shield.

Dave WD9BDZ

Dave

I'd agree with your statement if "matched" doesnt refer to *impedance*
match.

Jerry

"Cecil Moore" wrote in message
...
Jerry Martes wrote:
How wrong would it be to say that the *coax* part of the line doesnt
radiate at all?

The physical construction of the coax (ideal version) ensures
that the inside of the coax doesn't radiate because, for
ideal coax, the internal currents are perfectly balanced.
Any unbalance in the currents is forced to the outside shield
by the laws of physics.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil

I failed to emphisze that any current on the outside of a coaxial
transmission line are out of the bounds of the defination of Coax.

Jerry

Reg wrote, most lucidly,
"Found a corkscrew and I've just opened the Californian. I'd like to
try some of your Oregon stuff - do you have any. ;o) "

Why, yes, I do. Picked up a decent stash over the Indepencence Day
(that's US independence from England...) holiday a couple months ago,
at a nice wine and arts fair in Eugene.

Do _you_ have any? Are there any good English wines I should try when
I'm next in the neighborhood?? (Did Monty Python ever do a skit about
English wines to match the one they did about "Fine Australian Table
Wines"?)

Beats babbling on about old wives any day.

Cheers,
Tom

David G. Nagel wrote:

What I was taught is that in a properly installed antenna system the
coax will not radiate. If the antenna is not properly matched to the
coax you get current flow along the outside of the coax shield.

Dave WD9BDZ

It's too bad people are being taught this. As a number of others have
correctly said, impedance match has nothing to do with whether or not a
coax (or symmetrical twinlead line) radiates. Radiation is due to other,
unrelated causes.

Roy Lewallen, W7EL

David G. Nagel wrote:

SNIPPED

What I was taught is that in a properly installed antenna system the
coax will not radiate. If the antenna is not properly matched to the
coax you get current flow along the outside of the coax shield.

Dave WD9BDZ

A balanced antenna fed with balanced line, and the line goes away from
the antenna perpendicular [90 degrees angle] for a minimum of 1/4
wavelength is a properly installed antenna system: [line has minimum or
no radiation]

A balanced antenna fed with balanced line, and the line goes away from
the antenna non-perpendicular [other than 90 degrees angle] for a
minimum of 1/4 wavelength is an improperly installed antenna system:
[line will radiate]

A balanced antenna fed with un-balanced line, and the line goes away
from the antenna perpendicular [90 degrees angle] for a minimum of 1/4
wavelength is an improperly installed antenna system: [line will radiate]

A balanced antenna fed with un-balanced line, and the line goes away
from the antenna non-perpendicular [other than 90 degrees angle] for a
minimum of 1/4 wavelength is an improperly installed antenna system:
[line will radiate]

A balanced antenna fed with un-balanced line and a properly installed
balun, and the line goes away from the antenna perpendicular [90 degrees
angle] for a minimum of 1/4 wavelength is a properly installed antenna
system: [line has minimum or no radiation].

An un-balanced antenna fed with balanced line is an improperly installed
antenna and the line will radiate.

NEED I CONTINUE??

Ham op wrote:

A balanced antenna fed with balanced line, and the line goes away from
the antenna perpendicular [90 degrees angle] for a minimum of 1/4
wavelength is a properly installed antenna system: [line has minimum or
no radiation]

The line will have minimum or no radiation only if fed at the
transmitter end with a balanced feed. An unbalanced feed will create
unequal currents in the conductors, resulting in radiation. A
symmetrical (e.g., twinlead) line doesn't assure balance (equal and
opposite currents in the two conductors), and an unbalanced line will
radiate, regardless of its physical construction.

A balanced antenna fed with balanced line, and the line goes away from
the antenna non-perpendicular [other than 90 degrees angle] for a
minimum of 1/4 wavelength is an improperly installed antenna system:
[line will radiate]

True for both symmetrical line and coax. Radiation is due to common mode
current induced on the line. It can be reduced by inserting "current
baluns" (common mode chokes) in the line. A couple spaced about a
quarter wavelength apart are usually adequate.

A balanced antenna fed with un-balanced line, and the line goes away
from the antenna perpendicular [90 degrees angle] for a minimum of 1/4
wavelength is an improperly installed antenna system: [line will radiate]

The amount of common mode current and therefore radiation depends on the
length of the path along the outside of the coax to ground. A current
balun (common mode choke) at the feedpoint will reduce the current and
therefore radiation.

A balanced antenna fed with un-balanced line, and the line goes away
from the antenna non-perpendicular [other than 90 degrees angle] for a
minimum of 1/4 wavelength is an improperly installed antenna system:
[line will radiate]

This is due to induced common mode current. The mechanism is identical
to that when a symmetrical line is used.

A balanced antenna fed with un-balanced line and a properly installed
balun, and the line goes away from the antenna perpendicular [90 degrees
angle] for a minimum of 1/4 wavelength is a properly installed antenna
system: [line has minimum or no radiation].

Correct. A current balun at the feedpoint reduces the conducted common
mode current. Induced common mode current is prevented by symmetrical
feedline placement.

An un-balanced antenna fed with balanced line is an improperly installed
antenna and the line will radiate.

Coax feeding an unbalanced antenna will radiate just as much as twinlead
feeding an unbalanced antenna.

NEED I CONTINUE??

A lot of people have learned a list of handy rules like this without
having much of an understanding of where they came from or under what
circumstances they do and don't apply. For anyone interested in learning
more about common mode current, feedline radiation, types of feedlines,
and feedline radiation, I suggest taking a look at
http://eznec.com/Amateur/Articles/Baluns.pdf. It deals only with
conducted common mode current and doesn't discuss induced common mode
current -- I'll try to get together a supplement covering that topic
when I have time. There was some discussion on this newsgroup not long
ago about induced common mode current, but I can't locate the topic
right off. It should be possible to find it with a google search. Be
sure to also look at the work by Walt Maxwell, W2DU referenced at the
end of the balun article.

Roy Lewallen, W7EL

Walt,

I reported a model at the following link:

http://www.smeter.net/feeding/feedpowr.php

At resonance it reports a 'normal' pattern. Off resonance it reports up to 90%
feedline radiation. I intend to mimic the results this weekend. I will build a
10 meter dipole, misfeed it, an measure the results. I will let you know.

Dan

Walter Maxwell wrote:
On Tue, 30 Aug 2005 20:05:05 -0700, dansawyeror
wrote:


I have tried several parameters and have gotten results from a very low level
with a close match to over 90% of power radiated in the feedline when the dipole
resonance is far from the transmit frequency.

We may use this model for a couple of things. It is available and it predicts
radiation. That gives the opportunity to create a test. I for one are willing to
experiment.

Dan


Will you please describe the details of your experiment where you
claim 90% of the power is radiated from the feedline? How did you make
this measurement?

Walt, W2DU

Reg Edwards wrote:
I am truly disappointed with the long-running discourse on balanced
and unbalanced feedlines and the power radiated therefrom. It's been
going on for years.

Nobody, especially poor novices, has ever learned anything from it.

99% of it is bafflegab.

Few of us understand what on Earth is being waffled about. And those
who do, prefer not to waste their time by joining in.

The reason I'm making this seemingly outrageous statement is that
NOBODY HAS EVER QUANTIFIED, not even once, what they are waffling
about. This demonstrates a great ignorance of the subject.

(Remember what Lord Kelvin said about the ability to measure and
quantify what it is you are gabbing about and how that ability is
directly related to what you really know about it.)

Perhaps somebody might be prepared to state the power actually
radiated from feedlines in watts. At least it may create the
impression you know what you are talking about.

It might possibly be at such a low level that, in the great majority
of cases, it's not worth all the megabytes of bandwidth which are
wasted on it.

As an unbiased World Citizen, I now find myself half-way down a bottle
of Merlo, 2000, a produce of France. But I have in reserve some decent
Californian stuff.

May I say how saddened I am to learn about the terrible disastrous
storm which has befallen some of the Southern states.
----
Reg, G4FGQ


Instead of sitting around for years reading the "bafflegab" and then
complaining about it, why didn't you QUANTIFY it yourself and report it so
as to make yourself useful?

John

dansawyeror wrote:
At resonance it reports a 'normal' pattern. Off resonance it reports up
to 90% feedline radiation. I intend to mimic the results this weekend. I
will build a 10 meter dipole, misfeed it, an measure the results. I will
let you know.

Try "misfeeding" a 10m dipole with N*1/2WL 450 ohm ladder-line
through a good choke and get back to us. (N is a natural number)
--
73, Cecil http://www.qsl.net/w5dxp

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"Walter Maxwell" wrote
Will you please describe the details of your experiment where you
claim 90% of the power is radiated from the feedline? How did you
make
this measurement?

==================================

Walt,

If you erect a 10 meter 1/2-wave dipole and center-feed it with a 50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

SWR on the line will be about 1400 and the amount of power available
will not be very great.
----
Reg.