Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: Dressing RG6
Date: Wed, 15 May 2024 11:03:22 +0200
Organization: A noiseless patient Spider
Lines: 44
Message-ID: <v21tl5$pcju$1@dont-email.me>
References: <v204qu$99qs$1@dont-email.me> <v206dp$9pib$1@dont-email.me>
 <v20ads$aoqc$1@dont-email.me> <20240514b@crcomp.net>
 <66h74j1vfmbjvvl98jk1k017pimtinv2l5@4ax.com> <v20m3q$dgcq$1@dont-email.me>
 <v20n97$dq6r$1@dont-email.me> <20240514d@crcomp.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Date: Wed, 15 May 2024 11:01:25 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="326f6474fcc0b730bdcf516ef762bf66";
	logging-data="832126"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+KHJuEJ/PEXwVguhTPucBE"
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.13.0
Cancel-Lock: sha1:hfHdTl3vIU5XW+S26suRcl1qNes=
Content-Language: en-US
In-Reply-To: <20240514d@crcomp.net>
Bytes: 2977

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