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What kind of cable is this?

Discussion in 'Electronic Components' started by Marshall, Nov 12, 2004.

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  1. Marshall

    Marshall Guest


    I was out walking home from work yesterday here in Santa Clara, CA
    when I stumbled across a large spool of cabling by the side of the
    road. It appeared to have tumbled out the back of a truck as the
    plastic spool was scraped and cracked in places. I'm hoping someone
    can tell me what it's for. Here's a picture of it:

    The innermost bit is a copper cable ~1.5 mm in diameter. Surrounding
    this are two helically wound clear plastic tubes. They appear empty.
    I had a look at them with a hand lens and didn't see anything in them,
    so I'm guessing that they're there to isolate the aforementioned
    copper cable from the non-magnetic (i checked), copper colored braided
    sheathing. Around this sheathing is a black and white plastic braided

    Thank in advance =)

  2. Hal Murray

    Hal Murray Guest

    The innermost bit is a copper cable ~1.5 mm in diameter. Surrounding
    At high frequencies, the loss in the diaelectric is significant.
    My guess is it's coax intended for use at very high frequencies.

    I've seen drawing of rings of foam spaced along the coax every
    few diameters.
  3. It's definitely low loss coaxial cable, for UHF or higher freqs. And
    it's definitely _not_ made for outdoor use! The cable reel should give
    you some info or numbers to indicate the brand and type of cable.
  4. Ross Herbert

    Ross Herbert Guest

    There are a couple of clues from the pic.

    It is coaxial cable with a stranded centre conductor and a high
    density copper overall screen. The helically wound teflon (PTFE)
    spacer tape ensures good flexibility together with the stranded centre
    conductor. The fact that it has an outer sheath of probably nylon
    indicates it is intended for flexible interconnects. Unfortunately,
    without a part number or manufacturer name the operational
    characteristics would be a guess.
  5. Well, he would hae to measure the impedance or calculate it from the
    dimensions of the center conductor, dielectric and shield. I
    guesstimate that it's a low loss 50 ohm coax.
  6. Dave Platt

    Dave Platt Guest

    The innermost bit is a copper cable ~1.5 mm in diameter. Surrounding
    Yup. I don't know what specific type this is, but it's an
    air-dielectric RF cable. The spacer tubes are probably polyethylene
    or something like that. Likely intended for high-UHF and microwave
    frequencies. As it appears not to have any sort of waterproof outer
    jacket, it's certainly for indoor applications only... perhaps
    intended to be pulled through a conduit of some sort.
  7. Marshall

    Marshall Guest

    Hey All,

    Thanks for all the educated guesses. I'll closely inspect the big
    black plastic reel it's on when I get home from work today for part
    #'s. Yeah, this would've been a smart place to look...(blush).


  8. Marshall

    Marshall Guest

    Wow, great, so I have 100' or so of indoor UHF or microwave ready RF cable.
    Now let's see... you can cook with microwaves, then there's those
    microwave `relay' towers dotted on the hills around me and... Ummm... I
    seem to remember having a big, goofy UHF dial on my ancient TV set... So
    what in the Wide Wide World of Sports does one do with 100' of this stuff?!

  9. Ross Herbert

    Ross Herbert Guest

    Before we can tell you that you have to find out exactly what its
    specification is. So unless you can find a type number and
    manufacturer then anyone's guess as to application is not going to be
    entirely accurate.. However, you could possibly use it for esoteric
    interconnects on your hi-fi system but whether this would sound better
    is debatable.
  10. What Ross said. My first thought on "what to do with low-loss coax
    without a spec" was "audio interconnects", as without a spec it's
    impossible to know if it'll work in a particular RF application.
  11. Jamie

    Jamie Guest

    that is thread wrap, and at my present full time job we
    do make that from time to time.
    RG-62 (93 ohms)
  12. stuff?!

    Hey, it's that time of the year. You can tie those bundles of leaves
    and trash up with it. ;-)
  13. With the dielectric allowing the copper braid to move in relation to the
    center conductor, the cable could be microphonic if it was used with a
    high Z microphone.
  14. Ross Herbert

    Ross Herbert Guest

    Surely you jest...

    The main reason for a centre conductor of tightly twisted small guage
    strands and a very densely woven braid is to provide good flexibility
    together with a reduction in the generation of spurii, as would be the
    case when used as a flexible interconnect. The use of a double spiral
    continuous spacer also ensures good flexibility as well as ensuring a
    constant spacing when the cable is undergoing flexing.

    If this cable was microphonic at audio frequencies due to slight
    changes in the postional relationship of the centre conductor and the
    outer screen, how do you think these changes would affect its
    operation if it were used at UHF? Surely, - if you are correct, - it
    would create major problems at higher frequencies by altering
    characteristic impedance, noise generation etc all of which would
    probably be most evident.
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