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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Dressing RG6
Date: Tue, 14 May 2024 23:49:45 -0000 (UTC)
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Jeroen Belleman <jeroen@nospam.please> wrote:
> On 5/14/24 23:46, Phil Hobbs wrote:
>> John Larkin <jjSNIPlarkin@highNONOlandtechnology.com> wrote:
>>> On Tue, 14 May 2024 19:22:12 -0000 (UTC), "Don" <g@crcomp.net> 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.
>>>> 
>>>> 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
> 
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 

-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics