Dipole SWR readings, trim antenna or call it good?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N6WZQ, Apr 14, 2019.

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  1. SM0GLD

    SM0GLD Ham Member QRZ Page

    How is it possible to get a resonance at 5.1MHz if the total wire length is 23ft + 45ft = 68ft.
    The wire needs to be close to 96ft for a 5.1MHz resonance.

    If the short wire is 23ft it will not reach the 10ft level starting at 35ft. Going strait down it ends at 12ft.
    Is the short wire hanging strait down?
    NH7RO likes this.
  2. AI3V

    AI3V Ham Member QRZ Page

    When you figure it out, please let us know.

    Folks have been looking for a hundred years for the length.


    Why are you using a balun (BALanced to UNbalanced) impedance matching device of that particular ratio on a UNbalanced feedine to a UNbalanced antenna ?

    What exactly is the feedpoint impedance of your antenna?
    NH7RO likes this.
  3. KF4ZGZ

    KF4ZGZ Ham Member QRZ Page

    If you are using a tuner and can get your swr down to where you are happy with it everywhere you want it ...... leave it alone.
    In other words, if it works, don't fix it!
    AA7QQ likes this.
  4. SM0GLD

    SM0GLD Ham Member QRZ Page

    A good question. Somebody has to answer it.
    If you have an OCFD fed at 33% it is a good thing to use a Guanella balun because it will provide some amount of common mode rejection.
    If you design for another offset feed closer to wire end there will be a point where it becomes useless to use a balun.
    I have designed an OCFD fed at 10% and for that design I used a 4:1 unun + a choke.
  5. AI3V

    AI3V Ham Member QRZ Page

    So exactly how far away from the middle does a wire change from balanced to unbalanced?

  6. SM0GLD

    SM0GLD Ham Member QRZ Page

    I have had the same thoughts as you have.
    I think it is a matter of how much CM current there will be in the balun core. The further away from center you get the more unbalance current there will flow in the core..
    There is so many successful OCFD design using 4:1 Guanella balun so I can't say there all wrong. But as I said I used a unun down at 10% feed point.
    Last edited: Apr 14, 2019
  7. N6WZQ

    N6WZQ Ham Member QRZ Page

    Sorry, should have been more clear on this. The antenna is oriented in an inverted V (not sure what the angle is). The short end is terminated at a ceramic dogbone then has about 10 feet or so of rope extending to the anchor point on the roof. The long end goes through a plastic anchor on the roof then continues about 10 feet across the yard to an anchor point on my wooden fence.
  8. N6WZQ

    N6WZQ Ham Member QRZ Page

    I realized last night that when I did the SWR readings it was with only half the coax feedline hooked up. Just did another sweep from inside the shack. Got vastly different readings, especially on 15 meters, 17 meters, and 60 meters.

    Old readings:
    6 meters-low 4, mid 3, high 3
    10 meters-low 2.4, mid 2.8, high4.8
    12 meters-3.2 throughout
    15 meters-low 12.4, mid 12, high 12
    17 meters-10 throughout
    20 meters-low 1.6, mid 2, high 2.5
    30 meters-6 throughout
    40 meters-low 2.4, mid 2, high 1.6
    60 meters-1.8 throughout

    New readings
    6 meters-low 2.7, mid 2.8, high 3.7
    10 meters-low 3.0, mid 3.4, high 3.7
    12 meters-4.0 throughout
    15 meters-low 6.6, mid 6.3, high 6.1
    17 meters-6.6 throughout
    20 meters-low 2.1, mid 2.2, high 2.4
    30 meters-4.5 throughout
    40 meters-low 1.7, mid 1.5, high 1.2
    60 meters-5.0 throughout
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You should probably just try it on the air and see how you do.

    20-30-40m are full of quite strong signals, so you should hear them; and when you call, they should hear you.

    If you don't, or they don't, it's not working that well.:)

    One issue, of course, is the whole thing is pretty low to the ground. The exact same antenna with the center at 60' and the ends at 20' or higher will certainly work better. But CW and FT8 are two modes where lots of quite weak signals are easily worked; SSB is tougher.
  10. WA8UEG

    WA8UEG XML Subscriber QRZ Page

    What Steve said above.

    At the height I wouldn't expect fantastic results but you should be able to make contacts. Not sure how long you have been on HF but many new comers want something that will allow them to work all bands because their rig works all bands when if you are limited on antenna space you will have more fun and more contacts picking a band and putting up a dedicated antenna for that band I.E. a half wave dipole for 40 meters which will also work on 15 but that's not a great addition at this point of the sunspot cycle. Another option would be a a parallel or fan dipole for 40 & 20.

    I can assure you on 6 meters with the antenna you will have very limited success, don't confuse SWR with performance.

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