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Help Identifying This Product

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD8RYP, May 7, 2012.

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  1. KD8RYP

    KD8RYP Ham Member

    I went to RadioShack looking for the old 300 ohm twin lead cable tv coax and they brought out this. I went ahead and purchased it because it was cheap. Is this still 300 ohm twin lead or if not will this still work for slim jim antenna design's?? (see pic attachments)

    73's KD8RYP (Andrew)

    P.S. I'm completely new at this, don't laugh to loud LOL
     

    Attached Files:

  2. NW9M

    NW9M Ham Member

    Hey don't worry, everyone starts out new!

    Anyway, yes that is 300 ohm twinlead. Sometimes it has a foam insulation between the 2 wires which seems to make it more dimensionally stronger than reducing any losses, but it is essentially the same stuff.
     
  3. WB2WIK

    WB2WIK Premium Subscriber

    Yep, it's 300 Ohm twin lead. Or so.:eek:

    Only problem with a lot of that stuff is the plastic insulation sticks to the wire very tightly and the wire is quite thin and fragile, so while stripping the insulation it's really common to break some of the wire strands, leaving you with something that's very weak.

    Be careful!
     
  4. KD8RYP

    KD8RYP Ham Member

    Thanks for the feedback!
     
  5. KF5FEI

    KF5FEI Ham Member

    If you are building a Nor-Cal Doublet for portable operation, or a J-pole, that is the stuff you want. Sometimes very hard to find. However, the clear stuff is made for indoor use, and will deteriorate if you leave it out in the sun for extended periods. Ace Hardware supposedly / allegedly has the brown stuff of similar construction.
     
  6. WA8UEG

    WA8UEG XML Subscriber

    I use to just take a match and melt the required amount of insulation off then clean it up with a razor blade.
     
  7. K0RGR

    K0RGR Premium Subscriber

    There could be a difference in velocity factors, which might throw your dimensions off a bit. I learned that trying to substitute the foam center twinlead for the old brown stuff in Jpoles. I would think the clear stuff would be fairly close, but I don't know.
     
  8. KD8RYP

    KD8RYP Ham Member

    I played around with it some today, and I got it down as low as a 2-1 swr. I'm pretty sure it's going to tune just fine once I get another chance to mess with it some more. I encased it in 3/4" pvc.
     
  9. K8JD

    K8JD Ham Member

    Twin lead is twinlead and coax is coax. Two entirely different types of feedline.
    The first is a BALANCED line and the second is UN BALANCED line
    Twinlead for TV antennas is 300 Ohm parallel conductor line, similar to the larger 450-600 Ohm "ladder line". The spacing and diamater can be plugged into a formula to calculate the impedance.
    Coax is COAXIAL conductor line where the center wire is one side of the circuit and the shield or outer conductor is the other side of the circuit. Again the diameter and spacing of the conductors determine the impedance of the line. TV coax is 75 ohms and coax used in radio, Commercial and Amateur is 50 Ohms.


     
    Last edited: May 8, 2012
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