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SMBs to relieve torsion on coaxes

Discussion in 'Electronic Design' started by [email protected], Mar 28, 2007.

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  1. Guest

    I'm building an extender for my scope. A problem I have is that the
    coax is very stiff. When I flip the module over, the torsion gets
    transmitted along the coax and it eventually snaps the pins right off
    the connector.
    Are there any connectors designed to allow the coax to turn while
    maintaining decent signal integrity?
    DC-50MHz, riding on 65VDC.
    I'm thinking SMBs. This is a one-of personal thing, it doesn't need to
    be great. If it snaps out once in a while, it's not a big deal.
    Any clever ideas out there?
  2. Rich Grise

    Rich Grise Guest


    Good Luck!
  3. Guest

    Too big.
  4. John Larkin

    John Larkin Guest

    MCX's are even turnier than SMB's, which can have a lot of retention
    force. And there is tons of cheap MCX stuff on ebay.

  5. Guest

    Suhweet! I wish the datasheets specified "turniness" though.
  6. Rich Grise

    Rich Grise Guest

  7. Steve

    Steve Guest

    I use Hirose x.FL connectors (Digikey). These are very small, good to
    several GHz, and they latch very well. You can't really make your own
    cables. I buy 12 inch cables and cut them in half to solder one end into RF
    prototypes. For disconnect or production test, mount the cheap SMD female
    recept on the circuit board. Hirose makes several sizes of this style
    connector, but adapters might not be available for all of them. The SMA
    adapter is the biggest expense, but they seem to last a long time. Hirose
    sells a disconnect tool, but a strong fingernail will pop them apart. They
    spin nicely, but the 12" cable will be so flexible I doubt it will matter.
  8. john jardine

    john jardine Guest

    Dunno what the "very stiff" stuff may be but for test leads I use RG174u
    coax. It's only 2.8mm and very flexible.
  9. Guest

    Plenum RG-62U that's been on a reel for 15 years. I need 93 ohm coax
    so as not to load the tube drivers. Oh man the trouble I went through
    to get that coax working. As plenum cable, the center conductor was
    silver-plated steel. So I got some 22AWG silver-plated stranded wire.
    I managed to strip the Teflon off lengthwise, solder it on the end of
    the steel wire, and "fish" it through the 4 feet lengths of coax I
    Then I made another jig to score the very stiff outer jacket of the
    coax. Every three inches I scored the circumference down to the braid.
    Now I have flexible 93 ohm coax that tests very nice in the real
    world. But it's still so torsionally stiff it snapped a pin off a
    vintage Blue Ribbon connector.

    I'm a bit anal because I calibrate the plug-ins outside the scope,
    then when it's in the scope I don't want to have to tweak it because
    the impedance of my cables was off.

    The "real" extender has never shown up on eBay in the four years I've
  10. john jardine

    john jardine Guest

    You've the patience of 'Jobe' 'Job'? :)
    If it's the 547 'scope, at 50MHz (i.e near DC!) would have thought the
    cabling would be barely noticeable. But yes, I'm also loathe to let
    something be if I know I can do something about it.
  11. JeffM

    JeffM Guest

  12. Guest

    I'm crazy. I also need my 1S1 back in service.
    Good guess, that's what it is. Nice scope in winter. Now that it's
    getting warmer, not so much... :)
    Yeah it actually wasn't that hard to tweak the cables. I figure since
    my braided 22AWG has the same O.D. as the steel, I stay pretty close
    to 93 ohms, as long as I don't mush the dielectric too much out of

    It's really just a question of having the same results when I take the
    extender off and jam the plug-in in the scope. Worked until the pin
    snapped off.
  13. joseph2k

    joseph2k Guest

    Since plenum conditions do not apply, just get some superflex class coax.
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