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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: Dressing RG6
Date: Tue, 14 May 2024 23:33:35 -0000 (UTC)
Organization: A noiseless patient Spider
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Jeroen Belleman wrote:
> Phil Hobbs wrote:
>> John Larkin wrote:
>>> Don wrote:

<snip>

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

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

Note.

[1] Whitlock cynicism can be ignored:

    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,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.