8 responses

  1. Jorge EA2LU
    29/01/2012

    Why not detuned the 23m tower to try his effect?
    GL and QRV for any help from my little experience.
    EA2LU

    • Tobias
      30/01/2012

      Hi Jorge,
      detuning a tower is in my experience not that easy. Basically these are the next steps how I plan to proceed:
      1. Measure the resonance frequency of the tower (N6LF has done great experiments)
      2. When I know the resonance frequency I can generate a NEC2 Model
      3. Add slooping wires from the top of the tower in order to tune the tower.

  2. LB3HC, Marius
    05/02/2012

    Hi there!

    Have you considered that you may perhaps measure the F/B ratio too close to your TX site? You should be about 10 lambda away which is 1,6km km on 160m.

    Have you measured the currents in the two antennas ? (You may have to increase drive level and use a current transformer(s) to do that with a current transformer). It is the relative ratio of currents and the phase of the currents relative to each other that should give an indication whether this antenna actually operates as intended.

    To check if other structures radiate, I would suggest you would do current measurements on your separate tower legs with a split core current transformer. If the current is near the current in your verticals you may have a clue to what is going on.

    73
    LB3HC

    • Tobias
      06/02/2012

      Thanks for your comments Marius!
      A distance of almost 2 Lambda isn’t that bad. With this technique my friend Hannes, DK1NO has successfully measured all of his vertical lowband arrays. Also from a mathematical point of view I don’t see the necessity to go as far as 10 Lambda. Bear in mind that the electrical nearfield component decrease by the power of three (1/r^3) with the distance.
      Measuring the current in the wires is a good idea and I have already 4 current probes in the box. Unfortunately I had no proper Oscilloscope available on site.
      Rudy, N6LF has dedicated quite some time on measuring the influence of towers. In one of his papers he measures the resonance frequency of the tower with an attached loop. I already bought the components. When I’m next time back at the contest station I’ll give it a try.
      73 Toby

  3. MMM
    23/02/2012

    Mozilla just for you but I can’t even give you tumbs down :-) Let see if this goes thru. Any progress with 2 verticals?
    73 de Mario, S56A, N1YU

    • Tobias
      23/02/2012

      Hey Mario,
      I’m glad to see that you finally moved on to a proper browser 😉

      Yes, there are news. This weekend I have planed to measure the resonance frequency of the two towers. N6LF has described a way to measure it with a coupling loop and observing phase changes over frequency.

      In the meantime I did some additional tests. By connecting and disconnecting the koax to ground I could see a clear change in the f/b (peaking 10dB between 1900-2000kHz). So I suppose this confirms the theory that the tower(s) is/are influencing the 160m antenna.

      73 Tobias

    • Mario, S56A
      23/02/2012

      I moved temporarely just for you. Cheaper than Paypal :-) GL with 3 verticals, Herr Amigo!

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