On Sep 1, 9:52*pm, Owen Duffy wrote:
wrote in news:6f4f9e36-af26-4f1b-9244-383494f77b26
@c58g2000hsc.googlegroups.com:



On Sep 1, 3:25*pm, Cecil Moore wrote:
wrote:
...
Actually, 1000 ohms is pretty liberal. For instance, on
15m, the G5RV coax sees 36+j230 ohms or about 233 ohms.
The balun needs to be 10x that value or 2330 ohms.
--
73, Cecil *http://www.w5dxp.com

Why not 500 ohms, assuming a 50 ohm source and transmission line?

The common mode impedance of the balun acts in the common mode
transmission line (which is mutually coupled to the nominal radiator).

How is the differential mode transmission line characteristic impedance
relevant to the determination of common mode current in the antenna
system scenario described?

Owen

For a balanced transmission line, the characteristic impedance is not
expressed in differential mode terms, it IS common mode so I do
not know why you ask about differential mode characteristic impedance.
I never mentioned it. The characteristic impedance of a ladder line
for example
might be expressed as 600 ohms. That 600 ohms assumes common mode
conduction, as charateristically transmitted in a balanced line,
Differential mode impedance is assumed for un balanced transmission
line conditions.

wrote:
For a balanced transmission line, the characteristic impedance is not
expressed in differential mode terms, it IS common mode so I do
not know why you ask about differential mode characteristic impedance.

Well, there's your problem. In a properly functioning
transmission line, whether balanced or unbalanced, the
currents in the two conductors are differential, not
common-mode. The two currents are equal in magnitude
and 180 degrees out of phase and their fields tend
to cancel which minimizes radiation.

Common-mode currents only occur when the two currents
are not perfectly differential, i.e. not equal amplitudes
and/or not 180 degrees out of phase.
--
73, Cecil http://www.w5dxp.com

On Sep 3, 7:18*am, Cecil Moore wrote:
wrote:
For a balanced transmission line, the characteristic impedance is not
expressed in differential mode terms, it IS common mode so I do
not know why you ask about differential mode characteristic impedance.

Well, there's your problem. In a properly functioning
transmission line, whether balanced or unbalanced, the
currents in the two conductors are differential, not
common-mode. The two currents are equal in magnitude
and 180 degrees out of phase and their fields tend
to cancel which minimizes radiation.

Common-mode currents only occur when the two currents
are not perfectly differential, i.e. not equal amplitudes
and/or not 180 degrees out of phase.
--
73, Cecil *http://www.w5dxp.com

Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase. If they weren't, the CM
choke could not act to cancel them and you would need differential
mode chokes to get rid of them. On your balanced feedline, the voltage
at any point is delta between the amplitude of line 1 and 2.

wrote:
Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase.

You are 100% wrong. From "The IEEE Dictionary":
"common-mode (1)(general) The instantaneous algebraic
average of two signals applied to a balanced circuit,
both signals referred to a common reference."

The "instantaneous algebraic average of two signals"
180 degrees out of phase is ZERO.
--
73, Cecil http://www.w5dxp.com

On Sep 3, 7:12*pm, Cecil Moore wrote:
wrote:
Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase.

You are 100% wrong. From "The IEEE Dictionary":
"common-mode (1)(general) The instantaneous algebraic
average of two signals applied to a balanced circuit,
both signals referred to a common reference."

The "instantaneous algebraic average of two signals"
180 degrees out of phase is ZERO.
--
73, Cecil *http://www.w5dxp.com

So that means I get 0 volts when I touch one side of the 120V in my
electrical service to the 120V other side? I was afraid I might see
240V.

wrote:
So that means I get 0 volts when I touch one side of the 120V in my
electrical service to the 120V other side? I was afraid I might see
240V.

If those signals are equal in amplitude and 180 degrees out
of phase, it means they are *differential*, you will see 240v,
and you had better not short them together. OTOH, if they are
common-mode signals, they are in-phase and you can short them
together to your heart's content - no current will flow.

Again, you seem to have the IEEE definitions of "differential"
and "common-mode" exactly reversed in your head.
--
73, Cecil http://www.w5dxp.com

On Sep 3, 7:25*pm, Cecil Moore wrote:
wrote:
So that means I get 0 volts when I touch one side of the 120V in my
electrical service to the 120V other side? I was afraid I might see
240V.

If those signals are equal in amplitude and 180 degrees out
of phase, it means they are *differential*, you will see 240v,
and you had better not short them together.

OTOH, if they are
common-mode signals, they are in-phase and you can short them
together to your heart's content - no current will flow.

Again, you seem to have the IEEE definitions of "differential"
and "common-mode" exactly reversed in your head.
--
73, Cecil *http://www.w5dxp.com

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

Cecil Moore wrote:
wrote:
Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase.

You are 100% wrong. From "The IEEE Dictionary":
"common-mode (1)(general) The instantaneous algebraic
average of two signals applied to a balanced circuit,
both signals referred to a common reference."

The "instantaneous algebraic average of two signals"
180 degrees out of phase is ZERO.


--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

Cecil Moore wrote:
wrote:
Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase.

You are 100% wrong. From "The IEEE Dictionary":
"common-mode (1)(general) The instantaneous algebraic
average of two signals applied to a balanced circuit,
both signals referred to a common reference."

The "instantaneous algebraic average of two signals"
180 degrees out of phase is ZERO.

Cecil:

You must be getting old ... stop man! :-)

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

On Sep 3, 10:56*pm, John Smith wrote:
Cecil Moore wrote:
wrote:
Nope. The CM choke works precisely because the common mode currents
are mirror images, 180 degrees out of phase.

You are 100% wrong. From "The IEEE Dictionary":
"common-mode (1)(general) The instantaneous algebraic
average of two signals applied to a balanced circuit,
both signals referred to a common reference."

The "instantaneous algebraic average of two signals"
180 degrees out of phase is ZERO.

Cecil:

You must be getting old ... stop man! *:-)

Regards,
JS

--
It is like a nightmare where the public servants are the people which
the police are supposed to protect us from!

Yes, ZERO with respect to the isolated reference point. They are
measured with respect to each other, not ground. No current should
flow through the ground line if the feed is perfectly balanced.