Is a 1:1 vswr allways the lowest loss on a transmission line?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AI3V, Dec 13, 2019.

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  1. AI3V

    AI3V Ham Member QRZ Page

    Stay tuned for the answer ! :p

    (Here is a hint: the answer is no!)
     
  2. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    The correct answer is also why ladder line has a lot less loss than coax.....it's not for the reasons normally given.
     
    K0UO likes this.
  3. W8AAZ

    W8AAZ Ham Member QRZ Page

    Are you gonna say it depends on which end you measure it at?
     
  4. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Absolutely! Have you ever seen a length of coax that's been operated with very high SWR with a lot of power? At every current loop, the coax is "dented."....where the dielectric melted because of the copper getting hot at those points.
     
    W2VW likes this.
  5. AI3V

    AI3V Ham Member QRZ Page

    Click here for a clue

    Rege
     
  6. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Another neat trick is to build some ladder line out of very thin Nichrome wire (very lossy stuff). Run a few hundred watts into a dead short at the far end. The nichrome will glow red at the high current points, 1/2 wavelength apart.
     
    K0UO likes this.
  7. AI3V

    AI3V Ham Member QRZ Page

    Now what could you do (assuming equal power) to minimize current on a wire?

    Rege
     
  8. AG5CK

    AG5CK Ham Member QRZ Page

    Raise the impedance of the load and increase voltage.
     
    AI3V likes this.
  9. AI3V

    AI3V Ham Member QRZ Page

    full explanation here

    But here is the good part:

    [​IMG]

    Note the red/black line.

    Also note, that while the x axis is calibrated in feet, think in terms of wavelength. The actual line loss (3.2:1 vswr in this example) is less than the matched line loss for all transmission line lengths less than about 56 feet , or, 1/4 wavelengths! (Velocity factor corrected)

    Rege
     
  10. N8CMQ

    N8CMQ Ham Member QRZ Page

    Like an ignition system in a car, very high voltage, high impedance transmission line and an even higher load impedance.
    Even with mismatched impedances, the majority of power reaches the load. And that is with pulsed DC!
     
    AI3V likes this.

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