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non magnetic coax

Discussion in 'Electronic Design' started by Daniel, Oct 6, 2008.

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  1. Daniel

    Daniel Guest

    Hello,

    has anybody a source of non-magnetic RG174, RG178 or similar coaxial cable?



    Daniel
     
  2. Rich Grise

    Rich Grise Guest

    This doesn't make any sense. There is nothing magnetic about coax, unless
    it's in a coil creating a magnetic field, which isn't the coax's fault.

    Hope This Helps!
    Rich
     
  3. Guest

    A tinned shield would have some nickel in it, right?
     
  4. Tom Bruhns

    Tom Bruhns Guest

    Perhaps Belden types 7805 or 7805R? They apparently have a solid
    copper center conductor instead of stranded copper-clad steel.

    Cheers,
    Tom
     
  5. Tom Bruhns

    Tom Bruhns Guest

    You should try holding a magnet near normal RG-174/U sometime.
     
  6. Daniel

    Daniel Guest

    unfortunately nearly everything is magnetic. Most cables have steel
    conductors that are strongly magnetic. Even if they have no steel, many
    cables and connectors (everything that is gold-plated) have nickel
    adhesion layers below the gold. I am doing ferromagnetic resonance
    experiments, in these I can see the absorption from the cables. Our
    samples are very thin films (around hundred nm), so even a very thin
    metal film left from machining will cause a signal as big as the sample.
    Many people have problems with ferromagnetic resonance caused probably
    by the dielectric of microwave connectors, even though nobody really
    knows the reason.

    Daniel
     
  7. Daniel

    Daniel Guest

    Hello Tom,

    thanks for the idea.

    Daniel
     
  8. Daniel

    Daniel Guest

    I don't know, do you know a source for that info?
     
  9. Bill Sloman

    Bill Sloman Guest

    I just checked out an example of semi-rigid coax, and the one I looked at
    used copper for the outer conductor and silver-plated copper (SPC) for the
    inner.

    http://www.micro-coax.com/pages/pro...axial/Semi-RigidDetails.asp?ID=UT-085C-TP-M17

    Unfortunately, when I checked out RG402 and RG405 - the semi-rigid coax that
    you can buy from most broadline distributors - all the manufacturer's data
    sheets that I could find used silver-plated copper-clad steel wire for the
    inner conductor (also known as silver-plated copper weld SPCW). Many of
    Micro-coax's semi-rigid cables use the same centre conductor, but they do
    seem to use silver-plated copper centre wires in at least some of their
    cables - I didn't dig deep enough to find out why.

    Semi-rigid cable is nice stuff, but expensive, and if you can't get it from
    a distributor you quite often have to buy quite a lot more than you need.

    If you called up a local manufacturer of semi-rigid cable and told them what
    you needed and why you needed it you might be able to get a big enough free
    sample out if them to enable you to check out the approach.
     
  10. MooseFET

    MooseFET Guest

    Belden 9221
     
  11. Guest

    Yup I needed this to run RF to our optical pumping apparatus. Belden
    9221 010. Newark part number 05F1809. The core is all copper, The
    impedance is 75 ohms.

    George Herold
     
  12. Daniel

    Daniel Guest

    thank you all for your help, I've ordered both 9221 and 7805, I'll post
    the results soon.


    Daniel
     
  13. Rich Grise

    Rich Grise Guest

    Well, it didn't take long for my ignorance to get corrected. ;-)

    If you learn something new every day, does that mean I can go back to bed
    now? ;-)

    Thanks!
    Rich
     
  14. Tom Bruhns

    Tom Bruhns Guest

    :) I have a friend that often says, "Any day you learn something new
    is a good day." I have lots of good days, and I'm thankful for them.
    Well, OK, especially the ones where the learning isn't too painful or
    costly.

    Cheers,
    Tom
     
  15. Rich Grise

    Rich Grise Guest

    Well, I must admit I wasn't very confident, having seen copperclad steel
    cores. But it never occurred to me that that was what the OP was probably
    referring to.

    Thanks for the correction. :)

    Cheers!
    Rich
     
  16. Guest

    In french we say "je vais me coucher moins niaiseux a soir", which
    roughly translates to "I'm going to bed less dumb tonight".
     
  17. Daniel

    Daniel Guest

    Hello All,

    both the Belden 8705 and the 9221 (75 Ohm) cable are nonmagnetic and
    work well.

    Thanks again for all your ideas

    Daniel
     
  18. Tom Bruhns

    Tom Bruhns Guest

    Slightly off-topic: another friend pointed out an interesting
    property of RG-174/U -- the type with the center conductor of copper-
    clad steel strands. Most coax shows attenuation (in dB/unit length)
    proportional to the square root of operating frequency, at least where
    the frequency is high enough that skin depth is smaller than the
    thickness of the conductors and low enough that dielectric loss isn't
    significant. But because the copper on the center conductor of the
    RG-174 is so thin, about a mil, and because skin depth in the magnetic
    steel core is extremely small, the copper loss--and therefore the
    attenuation--is nearly constant over a range of frequencies up to
    roughly 10MHz. This can occasionally be an advantage.

    Cheers,
    Tom
     
  19. Guest

    Oh, is the 8705 50 ohm? That would be nice.

    George Herold
     
  20. Guest

    You can check the wiki to verify nickel is magnetic. However, it turns
    out nickel is only used in high temperature solder.
     
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