Is 450 ohm twinlead better

Discussion in 'General Technical Questions and Answers' started by K0CMH, Mar 12, 2008.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: Left-3
ad: MessiPaoloni-1
ad: Subscribe
ad: L-MFJ
  1. K5RCD

    K5RCD XML Subscriber QRZ Page

    The 3 types:

    300 ohm twin lead.
    [​IMG]



    450 ohm (often called ladder line) is actually window line.
    [​IMG]



    True "ladder line" open wire feed line. 650 ohm in this case.
    [​IMG]
     
  2. AC0FP

    AC0FP Ham Member QRZ Page

    I use both, my EDZ for 15 meters uses 300 ohm window line and my 20 meter vertical center fed dipole uses 450 ohm window line. Both antennas are usable 40 through 10 meters. However with the high VSWR on the feedline, when used on certain bands, the 450 ohm line provides less loss. As someone has mentioned the 300 ohm line is a lot more stealth .

    73,

    Frank
     
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    In the "goode olde dayes" various companies (including Belden) made what was called "transmitting twin-lead". This "stuff" was about 1 inch wide, had like 12 or 14 gauge stranded wire, and the insulation was very thick. It was rated for at least 5,000 watts and the impedance was 300 ohms.

    I was given around 100 feet of this "transmitting twin-lead" not long after I was licensed in 1959. Eventually I used it to feed a true Zepp antenna that was 270 feet long. That was the best wire antenna that I ever used even though it did not work on 15 meters (worked fine on 160, 80, 40, 20, and 10 meters). However, I had a 2-element yagi for 15 meters so did not need the wire antenna for 15. Of course back then you did not need an antenna tuner or even a balun since most transmitters could match at least 300 ohms and many could match 600 ohms, 1200 ohms, and a very few as much as 2000 ohms (i.e. the Hallicrafters HT-20).

    Glen, K9STH
     
  4. N5RFX

    N5RFX Ham Member QRZ Page

    DX Engineering makes nice 300 Ohm Window Line, even though they call it ladder line :)

    73,
    Mark N5RFX
     
  5. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page


    I have several hundred feet of the 300 ohm window line because it's smaller, lighter, and easier to deal with.

    For the record, if you are running less than say 150 feet of plain old TV twin lead and your not running more than say 300 watts or so, it will work very well. It is not much lossier than window or ladder line which is miniscule. The loss at HF frequencies using TV type twinlead is still far below that of coax and hardly worth mentioning. If you have it use it.......
     
  6. K0CMH

    K0CMH Ham Member QRZ Page

    That DX Engineering site is interesting??????

    It says their 300 ohm window line is 18 ga and rated for "full legal limit".

    Hummmmm, isn't 18 ga a little small for 1500 watts?
     
  7. G0GQK

    G0GQK Ham Member QRZ Page

    I make my own open wire feeder using single core panel wire or stripped out 3 core stranded domestic cable used for 240 V in the UK. I have my two feeders about four inches apart and have experienced very little variation in SWR whether its wet or dry.

    G0GQK
     
  8. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page


    I'm going to try and answer your question without telling you to build your own open wire line, or I'm way smarter than anyone else because, etc.

    300 ohm TV twinlead will work fine at HF for power levels up to about 300 watts. If you have a supply of it, use it and it will work just fine for you.

    Is window or ladder line better? Yes, but not that much so just use what you have.
     
  9. KA0GKT

    KA0GKT Ham Member QRZ Page

    The impedance at the input to any transmission line will be the characteristic impedance of the transmission line only when the transmission line is terminated in the line's characteristic impedance.

    If the transmission line is a multiple of 1/2-wavelength (when the transmission line's velocity factor is taken into consideration) the terminating impedance will appear at the input to the transmission line. So, a piece of 400-Ohm transmission line 1-1/2 wavelengths long terminated with a 50-Ohm load will have an input impedance of 50-Ohms.

    Of course, as the electrical length of a piece of transmission line moves away from a multiple of a 1/2-wave and moves closer to an odd multiple of a ΒΌ-wave, all bets are off. Remember that an electrical quarter wavelength of transmission line can act as an impedance transformer.
     
  10. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    If you have a decent tuner don't worry about the terminating impedance of the line. Just connect your 300 ohm twinlead to the antenna at one end and to your tuner at the other. Tune for minimum SWR and work the world.
     
Thread Status:
Not open for further replies.

Share This Page