135' Dipole Problems

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC9QQ, Oct 30, 2009.

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  1. KL7AJ

    KL7AJ Ham Member QRZ Page

    Au contraire. If you go far enough back in history, you'll find that the wide-range link-coupled tuner was in just about every ham shack in the country! The move away from tuners coincided with the advent of coax cable, which required a fairly good match to work decently. We actually LOST ground in flexibility with the "convenience" of coax. So the renewed interest in antenna tuners is really back to the future.

    eric
     
  2. KL7AJ

    KL7AJ Ham Member QRZ Page


    Such a device has been in existence since the beginning of radio...the R.F. Ammeter. See my February QST article, "Keeping Current with Antenna Performance."

    Don't guess...measure!
     
  3. G3TXQ

    G3TXQ Ham Member QRZ Page

    Or an instrument that was around even before the beginning of radio ...... a thermometer ;)

    Steve G3TXQ
     
  4. G3TXQ

    G3TXQ Ham Member QRZ Page

    Eric,

    I agree entirely with your conclusions, but not necessarily totally with the analysis.

    If you look at all the impedances on the spreadsheet linked in my Posting #22, you'll see that there certainly isn't an even spread around 50 ohms - the majority are significantly higher. But then if you look carefully at the tuner loss figures you'll see that they are generally lowest in the mid-range, say 50-500 ohms.

    It's the extreme impedances at low frequency where the tuner losses are greatest. At the high end the 1417+j4146 impedance caused a tuner loss of 0.3db - a 4:1 balun would have improved that to 0.2dB. However at the low end the 4:1 balun causes the tuner loss to increase from 1.2dB to 2.8dB with the 11-j35 impedance.

    It's pretty clear that if you are forced to select either 1:1 or 4:1 in a situation where impedances are unknown, the 1:1 is the better choice.

    73,
    Steve G3TXQ
     
  5. NL7W

    NL7W Ham Member QRZ Page

    Hi Eric,

    This is most likely the device to use. Reminds of me Occam's Razor once again -- that the simplest explanation or strategy tends to be the best one.

    :)

    Merry Christmas!





     
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