Bill's- HomeBrewed Pan Cake - 40 Meter TAK-tenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KA6KBC, Jun 12, 2008.

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  1. W8JI

    W8JI Ham Member QRZ Page


    I'll think you will find that antenna radiates from the feeder quite well when fed with twin line when the balun is down in the shack.

    To get rid of the feedline radiation you would have to have a very high common mode impedance at the antenna terminals, and then have a good balanced feed system in the shack.

    It is true that even with a good choke on the feeder the antenna will still make contacts. But to work "well", or work similar to full size antennas on lower bands, the feeder has to be involved in the radiating system.

    It would be possible to build a pretty efficient short dipole antenna, but probably not with pancake coils on the ends.

    73 Tom
     
  2. M3KXZ

    M3KXZ Ham Member QRZ Page

    Tom, please could you clarify? I thought the TakTenna was balanced and so with a good choke balun at the shack entry point of the twin lead then the currents on the twin lead should be canceling.

    Re effective short antennas....I've found in practise that my 3m tall top and bottom hatted vertical dipole works well. In use there doesn't seem to be any significant difference between this and a full size vertical dipole on 20, which is about 10m tall. So short antennas can work well, as you say. That TakTenna though.....toooooooo short!
     
  3. W8JI

    W8JI Ham Member QRZ Page

    The Tak antenna has some inherent unbalance in it. With a very small antenna a small amount of imbalance can create huge amounts of common mode. The is because the Q of the system is so high. There are huge amounts of stored energy in the induction fields around the element.

    You can do what you like a large fraction of a wavelength away, but the feeder has to be perfect balanced at BOTH ends or it will radiate. Just slapping twin line on an antenna that has similar ends is not enough.

    Short antennas with extended electric field areas (like a dipole) are a nightmare for balancing the antenna.

    73 Tom
     
  4. G3TXQ

    G3TXQ Ham Member QRZ Page

  5. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Tom.....this is a really good point. It also applies to small multiturn receiving loops, where one really has to take great pains to balance them if you want to get the proper nulling performance.

    On a related note.....
    I find it rather humorous that the Gap Titan assembly manual tells you NOT to put a choke balun in the the feedline because the performance will suffer. This is tacit admission by the manufacturer that it relies on the feedline for its operation! (Actually, with an effective decoupling scheme, the Gap works fairly well, except on 80 meters).

    Eric
     
  6. KA6KBC

    KA6KBC Ham Member QRZ Page

  7. VE6WTF

    VE6WTF Ham Member QRZ Page

    Careful, your starting to sound like my ex girlfriends.
     
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