Don't Earth a counterpoise ?

Discussion in 'General Technical Questions and Answers' started by M6LVC, Dec 1, 2016.

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  1. M6LVC

    M6LVC Ham Member QRZ Page

    In the summer I bought a sigma LW20 9:1 unun.
    I was disappointed with the performance.
    My longwire connected to my MFJ tunner seemed to work much better, although it was noisier.
    Last night I was reading through some old forums where someone mentioned using 4:1 & 9:1 unun's. They said don't connected the unun to ground, but use a 1/4 wave (my case 5m) counterpoise just above ground level in opposite Direction to the longwire and don't earth the counterpoise.
    I've only put out a few calls this morning since changing the antenna, seems a big improvement.

    My question is was some of my RF signal just going to ground ?
    Radio does have its own RF earth
    Many thanks in advance
     
    Last edited: Dec 1, 2016
  2. KK4YWN

    KK4YWN Ham Member QRZ Page

    The noise increase is a result of better operation. You'll need to start hunting for noise sources inside/around your home. Mix 31 clamp-on ferites will help.

    The problem with end-feds is one of perception. Most folks simply don't understand them. The first thing you have to accept is that there is no such thing as an end-fed. Near-end-feds are what they should be called because there is no way to match the very-end of a radiator: the impedance is simply too high. Moving the feedpoint away from the end lowers the impedance.

    The next issue is grounding the "ground side". This makes no sense. The end-fed was designed for use in blimps/zeppelins where an earth ground simply is not possible. Why do we earth ground these? Ellifino.

    Lastly: a counterpoise is not and never was connected to any part of the antenna. Its not a raised ground plane and its not a current return. Its simply a bunch of wires mounted a few feet above earth that help negate the effect of earth on RF currents. The earth acts as a resistor and consumes power. Adding a capacitor in series (counterpoise) creates a bit of a storage tank for the energy.

    I had given up on near-end-feds for awhile, but I'm beginning to like them again.
     
    AJ5J, KM4OYP, MM0HVU and 1 other person like this.
  3. G0JUR

    G0JUR Ham Member QRZ Page

    I hope you have that "rf earth" bonded to the mains earth point at the meter. why do you need an "RF earth" on the radio??
     
  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    A counterpoise, or 'radial" is the second half of an end fed antenna. In the beginning of radio and decades after, an ground/earth/soil connection, either at the radio, or at the antenna feedpoint was used as the return or second half of the antenna.

    Unfortunately, soil is a terrible conductor of RF. A radial or counterpoise of copper wire is thousands of times better at conducting RF and vastly reduces losses, making for a more effective antenna.

    Answer: Don't earth/ground the balun. Attach as many radials as convenient for your situation.

    Point for later discussion: Counterpoise became a misused term well before WWII. We really should use the term Radial, when discussing wires attached to verticals, end fed antennas, etc.
     
    M6LVC likes this.
  5. M6LVC

    M6LVC Ham Member QRZ Page

    your telling me to bond the RF earth to the mains earth !?
    it wouldn't be an RF earth then.

    I'm using a copper rod earth spike dedicated for the radio RF earth. one wire from the radio to the rod.
     
  6. G0JUR

    G0JUR Ham Member QRZ Page

    Last edited: Dec 1, 2016
  7. W6KCS

    W6KCS Ham Member QRZ Page

    Yikes!
     
  8. AI3V

    AI3V Ham Member QRZ Page

    Correct.

    There are 2 electrically identical half's to every antenna.


    By adding a 1/4 wave "counterpoise" you have added a very efficient 1/2 of the antenna.

    If you adjust the "long wire" part also to 1/4 wave you will find tuning to be much easier. Of course you will recognize this to be a ordinary 1/2 wave center fed dipole, or Hertz antenna.

    In general, a Hertz antenna works best the higher up it is.

    .........


    Close to the earth, some of the rf energy is absorbed by the dirt and converted to heat,

    Your seemingly low "counterpoise" improved your tx because it was much better than the random "other half' of the antenna" you were using before.

    I bet the wire connecting your rig to the "rf ground" has some length, a 1/4 wavelength here is useless as a connection to earth.

    Rege
     
  9. M6LVC

    M6LVC Ham Member QRZ Page

    the RF ground is less than 0.5m from the rig as itson the ground floor. Antenna looks like this https://i.imgur.com/I2AZJJU.jpg
     
  10. G0JUR

    G0JUR Ham Member QRZ Page

    That RF ground should be bonded to the supply meter ground point.
     
    W6KCS likes this.

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