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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: Dressing RG6
Date: Fri, 17 May 2024 03:40:17 -0000 (UTC)
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Jeroen Belleman wrote:
> Phil Hobbs wrote:
>> Jeroen Belleman wrote:
>>> Phil Hobbs wrote:
>>>> John Larkin wrote:
>>>>> Don wrote:
>>>>>> Phil Hobbs wrote:
>>>>>>> Phil Hobbs wrote:
>>>>>>>> Don Y wrote:
>>>>>>>>> I've several short (a few feet) lengths of RG6 that I
>>>>>>>>> would like to "strongly coerce" into assuming a particular
>>>>>>>>> dressing.
>>>>>>>>>
>>>>>>>>> Securing the cables to a stationary surface isn't practical
>>>>>>>>> without significantly lengthening them and distorting
>>>>>>>>> their "natural" routing.
>>>>>>>>>
>>>>>>>>> But, ISTM that I should be able to slip each cable into
>>>>>>>>> a comparable diameter copper (?) pipe and then use traditional
>>>>>>>>> tools to bend that pipe into the appropriate configuration.
>>>>>>>>> I'd have to observe constraints like minimum bend radius
>>>>>>>>> but are there other issues that I might "discover" down the
>>>>>>>>> road?
>>>>>>>>
>>>>>>>> You?re planning to make a random- length shotgun balun.
>>>>>>>
>>>>>>> Bazooka balun.
>>>>>>
>>>>>> 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.
>>>>
>>> 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.
>>>
>> 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.
>
> I did some comparative tests. The results are here:
> <https://jeroen.web.cern.ch/jeroen/coaxleakage/leakage.shtml>.
> There are a few references too.

To summarize:

Apparently Jeroen uses CK50 sheathed in copper tubing while his
colleague's cable is CKB50. The transfer impedance of all tested coax
cables converge at about 54 MHz - a cable channel's common lower
frequency range.

Don Y's primary takeaway from this thread may be to solder both ends
of his conformal copper to the coax screen underneath.

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.