wrote:
Again, you seem to have the IEEE definitions of "differential"
and "common-mode" exactly reversed in your head.

Really? Do you believe the currents in a resonant 1/2 wave dipole are
common mode or differential mode?

Assume it is a 1/2WL wire in free space. Where
is the common reference?

I've heard antenna currents called "common-mode"
currents but neither Kraus nor Balanis call those
currents "common-mode". They are usually called
"antenna currents" (in phase, radiating) vs
"transmission line currents" (out of phase, non-
radiating).

In any case, differential currents on a transmission
line are 180 degrees out of phase and ideally, non-
radiating. Common-mode currents on a transmission
line are in phase and radiate. The currents in a
folded dipole are in phase and radiate.

Within a ferrite toroid wired in a 1:1 current-choke-
balun configuration, common-mode current induces flux
in the toroid with virtually none from differential mode.
If the device is made out of turns of coax, the differential
currents never see the choking impedance.
--
73, Cecil http://www.w5dxp.com

wrote:
Cecil, if a transmission line operated in the way you think, it would
be radiating fields all along its length transmitting RF all along the
length of the line.

False! This is easy to visualize and prove. Given a 1/2WL
folded dipole fed with 300 ohm balanced line:

1. Do the out-of-phase differential transmission line
currents radiate? Ideally - NO!, because the fields
from the two wires engage in destructive interference
and cancel.

2. Do the in-phase antenna currents radiate? YES!, just
as they are supposed to do because the fields from the
two wires engage in constructive interference and re-
enforce each other.

Let's look at the balanced output terminals of the current
balun at the source. Instantaneous current is flowing out
of one terminal while instantaneous current is flowing into
the other terminal. I'm sorry, but that is differential,
transmission line current.
--
73, Cecil http://www.w5dxp.com

On Sep 4, 7:51*am, Cecil Moore wrote:
wrote:
Again, you seem to have the IEEE definitions of "differential"
and "common-mode" exactly reversed in your head.

Really? Do you believe the currents in a resonant 1/2 wave dipole are
common mode or differential mode?

Assume it is a 1/2WL wire in free space. Where
is the common reference?

There is none unless you choose to define one. You could go halfway
down the output choke and call it "common refrerence" or "isolated
ground" or whatever you want to call it. Since there usually no need
to reference it axcept perhaps for tutorial purposes, I wouldn't call
it anything. You could also reference it to earth ground but only if
you physically connected it to the aforementioned centertap.

I've heard antenna currents called "common-mode"
currents but neither Kraus nor Balanis call those
currents "common-mode". They are usually called
"antenna currents" (in phase, radiating) vs
"transmission line currents" (out of phase, non-
radiating).

In any case, differential currents on a transmission
line are 180 degrees out of phase and ideally, non-
radiating. Common-mode currents on a transmission
line are in phase and radiate. The currents in a
folded dipole are in phase and radiate.

The ideal transmission line is common mode and does not radiate
because the fields cancel as you said earlier. The dipole antenna is
ALSO common mode but the fileds do NOT cancel because the conductors
are physically 180 degrees apart from each other so they cannot
interfere with each other; instead the fields radiate into free space
rather than cancel each other out. It is rather simple really. It is
correct to call antenna currents "common mode currents". If the
currents on a transmission line are differential, how would (COULD)
they be converted to common mode currents on the antenna? We would
need a 180 degree phase shift somewhere. Answer: the currents on both
the transmission line and the antenna are common mode.

Within a ferrite toroid wired in a 1:1 current-choke-
balun configuration, common-mode current induces flux
in the toroid with virtually none from differential mode.
If the device is made out of turns of coax, the differential
currents never see the choking impedance.

Which explains why you should call it a balun and not a choke. If the
balun and source impedances match there should be no choking
impedance; maximum power trnasfer should occur.

--
73, Cecil *http://www.w5dxp.com

wrote:
The ideal transmission line is common mode and does not radiate
because the fields cancel as you said earlier. The dipole antenna is
ALSO common mode but the fileds do NOT cancel because the conductors
are physically 180 degrees apart from each other so they cannot
interfere with each other; instead the fields radiate into free space
rather than cancel each other out.

If transmission line currents were common-mode, they would radiate
like crazy and would be an antenna instead of a transmission line.
When one shorts the two wires together and feeds the system Marconi
style against ground, then the currents are common-mode. (Please
switch your news-reader to fixed font). A '+' indicates a connection,
not polarity.

+--------------------
| current reference
(V)
| Differential currents to antenna
+--------------------
Normal Transmission Line mode designed not to radiate


+----+------------------
| | current reference
(V) |
| | Common-mode currents (becomes antenna)
| +------------------
GND Marconi Style feed designed to radiate

If the
currents on a transmission line are differential, how would (COULD)
they be converted to common mode currents on the antenna? We would
need a 180 degree phase shift somewhere.

I'm glad you asked. When we take the last 1/4WL of transmission
line and open it up into a dipole, we have rotated one wire by
-90 degrees and the other wire by +90 degrees. That's a 180 degree
difference. The transmission line currents are 180 degrees out of
phase. The extra 180 degrees of physical rotation subtracts from
the 180 degrees in the transmission line for a total of zero
degrees (in phase) at the antenna feedpoint. This is explained
in detail in "Antenna Theory", by Balanis, 2nd edition, page 18.
I will try to duplicate it here using fixed font ASCII graphics.

In Phase Antenna Currents
--------------------+ +--------------------
| |
| |
+------------------+ |
(V) Differential |
+--------------------+
Transmission Line Currents

Note the out of phase currents in the transmission line results
in in-phase currents in the dipole antenna.
--
73, Cecil http://www.w5dxp.com

Sal M. Onella wrote:
"Mike Coslo" wrote in message
36...
Do your prayers make any difference, they really don't, because God knew
you were going to pray, and he knew his response. You had no choice. You
did what you did because God made you do it that way.

This of course means that God knows the predestination of every person he
created, which means that he knew that he was knowingly condemming a whole
lot of people to an eternity of torture.

I picked up on these and other inconsistencies in the early 1970s. I've
been an atheist ever since.

I wish some few atheists weren't such activists about it, though. It gives
us bad PR and turns atheism into a religion.

For me, a person is allowed to believe whatever they want, as long as it
doesn't affect me. Unfortunately, too many of them don't get that part
and want to force themselves on everyone.

Oddly enough, the greatest sermon, direct orders from the man himself is
ignored by these folk.

- 73 de Mike N3LI -

Mike Coslo wrote:

I was listening to a preacher just last night.

According to him, All is preordinated. God knows the outcome of everything
and every single thing that has and will ever happen. All is predestinated.
This has been known from before he created the unuverse

Predestinated?? Does that mean that God knows exactly when
you will end your 2-meter mobile QSO, lock up the car and
go inside the supermarket for the milk jug the XYL just told
you to pick up on the way home?

Jim, K7JEB

Jim, K7JEB wrote:
Mike Coslo wrote:

I was listening to a preacher just last night.

According to him, All is preordinated. God knows the outcome of everything
and every single thing that has and will ever happen. All is predestinated.
This has been known from before he created the unuverse

Predestinated?? Does that mean that God knows exactly when
you will end your 2-meter mobile QSO, lock up the car and
go inside the supermarket for the milk jug the XYL just told
you to pick up on the way home?


You got it. He won't tell you when you lock your keys in the car - even
when he already knows you're going to do it!

- 73 de Mike N3LI -

On Fri, 05 Sep 2008 14:19:28 -0400, Michael Coslo
wrote:

Jim, K7JEB wrote:
Mike Coslo wrote:

I was listening to a preacher just last night.

According to him, All is preordinated. God knows the outcome of everything
and every single thing that has and will ever happen. All is predestinated.
This has been known from before he created the unuverse

Predestinated?? Does that mean that God knows exactly when
you will end your 2-meter mobile QSO, lock up the car and
go inside the supermarket for the milk jug the XYL just told
you to pick up on the way home?


You got it. He won't tell you when you lock your keys in the car - even
when he already knows you're going to do it!

He won't answer your prayers for the phone number for AAA because he
already wrote it on your membership card he knew you left on the
dresser.

73's
Richard Clark, KB7QHC

Michael Coslo wrote:
You got it. He won't tell you when you lock your keys in the car - even
when he already knows you're going to do it!

Even before He told Pharaoh to let His people go,
He already knew Pharaoh was predestined to say no.
--
73, Cecil http://www.w5dxp.com

Richard Clark wrote:
On Fri, 05 Sep 2008 14:19:28 -0400, Michael Coslo
wrote:

Jim, K7JEB wrote:
Mike Coslo wrote:

I was listening to a preacher just last night.

According to him, All is preordinated. God knows the outcome of everything
and every single thing that has and will ever happen. All is predestinated.
This has been known from before he created the unuverse
Predestinated?? Does that mean that God knows exactly when
you will end your 2-meter mobile QSO, lock up the car and
go inside the supermarket for the milk jug the XYL just told
you to pick up on the way home?

You got it. He won't tell you when you lock your keys in the car - even
when he already knows you're going to do it!

He won't answer your prayers for the phone number for AAA because he
already wrote it on your membership card he knew you left on the
dresser.


If he was a person, he wouldn't be on my Christmas card list.


After I wrote that, I realized just how weird the statement was. Oh
well, I'll leave it for people's amusement or irritation.

Suffice it to say, the XYL wouldn't put up with that sort of behavior....


- 73 de Mike N3LI -