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mixing coax,Baluns, ladder line calculations

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by DAN13L, Dec 6, 2018.

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  1. DAN13L

    DAN13L QRZ Member

    I have a QTH where I have a shack only accessible via coax, a long run ideally overhead to a point where I wish to return to short run of coax buried in ground to feed a vertical nested multi band dipole.

    My theory is :-
    Coax to 9:1 balun to ladder line 450 ohm to 9:1 balun to coax to aerial.

    This cuts down my run considerably, I believe insulated 450 ohm ladder has less loss at HF frequencies than coax and is cheaper.

    Several people have said to try it, nobody as yet can point me to a calculator or say how it will perform other than suggestions of a 4:1 balun without explanation of why except it won’t tune allegedly.

    Thanks
     
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Cannot analyze this without knowing a lot more about your antenna(s), run lengths, frequencies/bands, specs of coax and ladder-line, balun designs, etc.
     
  3. DAN13L

    DAN13L QRZ Member

    6- 80 mDX commander nested vertical dipole kit
    Coax preferably LMR 400 or 600
    RG213 not preferred as losses at 54mhz awful.

    Run is:-
    shack coax 10m
    Ladder line 20m
    Coax to antenna say 6-10m

    The alternative is a 100m drum of LMR 400 or LMR 600 and a world of pain to get to where it needs to be.

    The property has a restrictive covenant and a non permanent guyed antenna structure avoids grief.

    Thanks
     
  4. AI3V

    AI3V Ham Member QRZ Page

    We need to know the actual "as installed" impedance at the antenna feedpoint, otherwise it's gigo.

    Rege
     
  5. KX4OM

    KX4OM Ham Member QRZ Page

    Joel Halas, W1ZR addressed in "The Doctor is In" almost the same exact situation in QST. You have to figure in the loss in dB for the 9:1 baluns at each end of the window line, about 1 dB loss each. His recommendation for a run of about 100 feet, it isn't worth it. He said for a thousand feet, his recommendation would be different. Sorry I can't name the issue; it is in about a foot high stack of nighttime reading QST and QEX issues upstairs.

    Ted, KX4OM
     
    K7TRF likes this.
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

  7. DAN13L

    DAN13L QRZ Member

    Hi thanks for the reply- this was exactly what I had been looking for and couldn’t find.

    Currently it looks as if losses v cost LMR 400 and see if there is way round covenant/ planning control etc
     

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