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From: John Larkin <jjSNIPlarkin@highNONOlandtechnology.com>
Newsgroups: sci.electronics.design
Subject: Re: Dressing RG6
Date: Wed, 15 May 2024 07:27:07 -0700
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On Wed, 15 May 2024 11:03:22 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:

>On 5/15/24 01:33, Don wrote:
>> 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?
>
>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

Two parallel coaxes can make an attenuator.

What was the coupled frequency response like?