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End Fed Wire Antenna w/ extendable fishing rod

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KM4SJS, Jun 16, 2016.

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  1. KM4SJS

    KM4SJS Ham Member QRZ Page

    Well I know the know it alls will chime in and suggest get a book, yada yada yada.. HOWEVER...

    I'm looking to build an END FED Wire Antenna to use on 10 & 6 for right now for home use and QRP...

    What would be the best Balun or Unun to use (self made) and should I put an inline insulator or trap on the wire some where..

    I plan on taking the 10' fishing rod, mounting it on some reduced PVC sections to give it more height... maybe push 20'...

    What do you think...
     
  2. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Can't you lay out any radials? Even one? You would have much better performance.

    p.s. If you are going to play with high impedance antennas you need a good tuner. I recommend a manual tuner, the matching range is usually much wider.
     
    KD6RF likes this.
  3. K4SAV

    K4SAV Ham Member QRZ Page

    If you have no counterpoise for this antenna then the feedline will become the counterpoise. A choke or current mode balun won't work with this antenna if it is placed at the antenna feedpoint. You will never get a choke with enough impedance and if you could get a choke with enough impedance, you would never be able to get any current into the antenna. You could put a choke on the feedline at about 1/4 wavelength from the antenna to remove some of the common mode currents on the shack end of the coax. Whether you need a matching network or balun depends on the length of the antenna and counterpoise and how much coax loss you can tolerate.

    With only a single wire for the antenna and no counterpoise you can expect high SWR and high coax loss.

    No I won't suggest you get an antenna book, as you were expecting. Trial and error is a good teacher and the lessons learned usually remain longer. Usually the first thing you learn is the antenna doesn't seem to work right. After much experimentation you can usually figure out why.

    Jerry, K4SAV
     
    Last edited: Jun 16, 2016
    AJ5J and KD6RF like this.
  4. AA7EJ

    AA7EJ Ham Member QRZ Page

    Jerry,
    "...no counterpoise for this antenna then the feedline will become the counterpoise..."

    Please explain why end feeding an radiator , for sake of argument assume 1/2 wavelength long , requires "counterpoise" while feeding same radiator at center apparently does not. May have missed it , but never heard anybody using counterpoise on a dipole antenna.


    Also " high SWR and high coax loss " statement is little misleading - coax loses due to high SWR are overrated, they are there but hardly "high".
     
  5. K4SAV

    K4SAV Ham Member QRZ Page

    It is impossible to feed a current from a source into anything without the same magnitude of current returning to the source. You can't violate this physical law. If you push current into an end fed wire, the same magnitude of current has to return to the source from somewhere else. The only other " somewhere else" available is the coax shield and it comes from there by capacitive coupling.

    A center fed dipole has a source for that return current, the other half of the antenna.

    How high is high? Well it depends on the antenna details, which we don't know. In order for the antenna to have a low SWR on one of the bands he would need just the right length of feedline and the right termination to ground (since the feedline is the other half of the antenna), Probability of hitting that is NIL. Typically with an end fed antenna using the feedline as the counterpoise, the SWR that the feedline sees will be in the range of 5 to 100 to 1. I would call that high.

    If you could end feed an antenna that has no counterpoise at all, the SWR will be infinity. Of course it wouldn't be much of an antenna since you couldn't force current into it, and it wouldn't radiate. You also can't physically build this antenna.

    Jerry, K4SAV
     
    AJ5J and KD6RF like this.
  6. AA7EJ

    AA7EJ Ham Member QRZ Page

    Thanks Jerry,
    the comment was NOT about high (antenna) SWR , it was about "high SWR coax loss".
    The distinction is important.
     
  7. WR2E

    WR2E Ham Member QRZ Page

    Way to hijack a guy's thread!
     
  8. G0JUR

    G0JUR Ham Member QRZ Page

    EFHW antenna's arte used a lot in the uk, sometimes without a counterpoise but this is usually at qrp power levels and employing some kind of 4:1 6:1 or 9:1 un un
    EFHW is best used witha quarter wave counterpoise.

    feeding an efhf can be tricky because you are feeding the high impedence point, several thousand ohms and its a high voltage point as well
     
  9. AA7EJ

    AA7EJ Ham Member QRZ Page

    Aren't you the guy who has given me the sermon about learning stuff?
    Way to kill an interesting subject .
     
  10. WR2E

    WR2E Ham Member QRZ Page

    Yup, that was me, the same guy who you so rudely chastised for giving you 'too much information', one and the same. I tried to help you and you spit in my face... the nerve.

    Not killing anything, you are. It's not your thread. Let the OP have his thread back.
     

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