Path: ...!2.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: "Don" Newsgroups: sci.electronics.design Subject: Re: Dressing RG6 Date: Fri, 17 May 2024 03:40:17 -0000 (UTC) Organization: A noiseless patient Spider Lines: 80 Message-ID: <20240516c@crcomp.net> References: <20240514b@crcomp.net> <66h74j1vfmbjvvl98jk1k017pimtinv2l5@4ax.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Fri, 17 May 2024 05:40:17 +0200 (CEST) Injection-Info: dont-email.me; posting-host="b79bb02819dcf9a8d2d07b1af4886e34"; logging-data="2118133"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/fLracpoCfhkInJj/y30Sp" Cancel-Lock: sha1:qedff3VKzQIdL7QHRUyq84O3Npg= Bytes: 4165 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: > . > 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.