Why is coax unbalanced ?

[K5JYD]

The comment abt there being a difference between the two conductors makes sense , the bigger the conductor, the less resisteance.
k5jyd

[K8ERV]

Just some food for thought.....

I have some big coax that has a hollow center conductor. Now do we have four paths? Is it now balanced?

Durn, now I won't get any sleep tonite.

TOM K8ERV Montrose Colo

[WB2WIK]

I had some unbalanced feedline but after six months of intensive therapy, it's better now and off all the meds.

[K8MHZ]

The comment abt there being a difference between the two conductors makes sense , the bigger the conductor, the less resisteance.
k5jyd

The correct term would be impedance. Also, for RF, it's not so much the size (cross-sectional diameter) but the surface area that affects the impedance due to skin effect.

That is why large RF conductors are hollow. Large diameter conductors will have no or almost no current flowing through the center of the conductor.

At 60 Hz, skin effect is much less than at RF, but even so the very largest conductors for 60 Hz are hollow. They are called 'iso-phase' conductors and are usually found connecting a utility sized generator to a very large transformer. I got to test some at a power plant. They were 18" in diameter, hollow, with cooling air passed through them. The operating voltage was 18,000 volts and the conductors were good for thousands of amps at that voltage.

[K1ZJH]

Just some food for thought.....

I have some big coax that has a hollow center conductor. Now do we have four paths? Is it now balanced?

No, but if you are exceptionally clever, and the coax large enough, you could use the hollow center conductor
for microwave wave guide.

[K5JYD]

Thanks Mark , its clear now.
k5jyd

[WB2UAQ]

If I eliminate the current flowing on the outside of the shield by use ,of say, a ferrite current balun, I assume I cud then call it a balanced line ?
k5jyd

Yes. That is what W2DU did. He threaded coaxial cable thru a large # of ferrite beads. The center conductor and the braid now float with respect to anything (might say floating with respect to ground or earth). You now have a floating 50 ohm source assuming 50 ohm cable. You can also wrap turns of coax on a toroid or rod and get similar results. 73,
Pete

[K8MHZ]

Yes. That is what W2DU did. He threaded coaxial cable thru a large # of ferrite beads. The center conductor and the braid now float with respect to anything (might say floating with respect to ground or earth). You now have a floating 50 ohm source assuming 50 ohm cable. You can also wrap turns of coax on a toroid or rod and get similar results. 73,
Pete

Ah, no, Walt (who is a friend of mine) did NOT change unbalanced line into balanced line by his ingenious use of ferrite chokes. What he did manage to do was to abate the shield of the feedline from radiating and acting as an antenna, as does the PROPER length of coax wound in a coil, with or without a toroid. None of this changes unbalanced coax into balanced feedline.

The source is the transmitter. Matching the impedance of the load and the source is called conjugate matching. Ferrites do not change the impedance of anything. They simply act upon unwanted radiation and keep it where we want it, in the antenna.

[K8MHZ]

Thanks Mark , its clear now.
k5jyd

It's my pleasure. Your question was a very good one, and as you can see by some of the respondents, it's also a question about a subject not clearly understood by all.

[WB8NQW]

In a balanced line neither conductor is connected to ground (chassis). A 3 conductor microphone cable (XLR termination) has a balanced pair of audio wires not connected to ground (chassis) and a grounded conductor usually a shield of some kind.
Coax is unbalanced because the shield is connected to ground (chassis) on at least one end and maybe both ends. I don't believe that skin effect or whether the current is on the inside surface or outside surface has anything to do with balanced or unbalanced.

73
Bob