Re: Dressing RG6

Bazooka balun.

The parasitic capacitance created between coax and its metal armor can open a Pandora's box of potential problems.

Danke,

Capacitance between the coax outer and the copper pipe? Proper coax shouldn't have any external field.

If the whole system is really coaxial, that’s true. Leaky shields, ground loops, and so on, will modify that.

Depending on the application, you may or may not care.

Cheers

Phil Hobbs

I've been putting coax inside copper tubes or braids to measure and/or reduce the transfer impedance (leakage). I did that to measure small signals in a particle accelerator, which typically has kicker magnets and RF cavities with kA currents and kV voltages nearby.

A colleague developed a special low transfer impedance coax cable for this sort of application. It had two screens with intermediate magnetic shielding. It was unpleasant to work with, because part of the magnetic shielding was a steel spiral foil tape that was razor sharp. But it worked really well.

Jeroen Belleman

Does a ferrite bead by any other name (eg metal armor) contain parasitic capacitance?

... A ferrite bead can be modeled as a simplified circuit consisting of resistors, an inductor, and a capacitor ...

Danke,

Empirical observation always trumps theory for me. Did you ground [1] the copper tubes or braids?

Note.

Q. What does "ground" mean? A. A fantasy invented by engineers to simplify their work.

_An Overview of Audio System Grounding & Interfacing_ by Bill Whitlock

Danke,

Interesting, thanks.

Is that better than real solid copper hardline or (my fave) RG402 semi-hardline?

I’d like to read more about it, if you have a reference handy.

Cheers

Phil Hobbs

Why can't he just use tie-wraps? Or hot-melt?

I means just what it says. Dirt.

What a simplistic suggestion!

This is the Yuniskis world we’re talking about, where nothing is ever so simple as it might seem.

You might as well suggest that Baer get a new computer!

(And in my world, RG-58 cables talk to each other all the time.)

Cheers

Phil Hobbs

Thank you.

The more one engineers something, the simpler it should get.

Both ends were connected to the connector shields. The point of the exercise was to reduce transfer impedance, which at low frequency (<1MHz) is simply proportional to screen resistance.

Jeroen Belleman

I did some comparative tests. The results are here:

Jeroen Belleman

Two parallel coaxes can make an attenuator.

What was the coupled frequency response like?

How about semi-rigid adhesive lined heat shrink tubing?

Just say your data below.

I didn't?

Jeroen Belleman

Ah sorry, this message didn't seem to get sent...

At low frequency, the transfer ratio was simply the ratio of screen resistance over characteristic impedance. At medium frequencies, a few octaves roughly around 1MHz, there was a dip, and above that a steady rise of about 10dB/decade.

Not all cables behaved the same. RG58 is poorly screened and doesn't have the dip. UT141 had a very deep dip.

Details at