Ham Radio - An end fed folded dipole experiment. Part 1, the idea and design.

Discussion in 'Amateur Radio News' started by KB7TBT, Jul 7, 2019.

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  1. K2XT

    K2XT Premium Subscriber QRZ Page

    It's not a folded quarter wave monopole, it's a half wavelength long transmission line. Nope, not even matching is going to work. It's not 150 ohms, 500 ohms, 2000 ohms, 25 ohms, or even 2 ohms. It's a short circuit where it is resonant which is where it was designed to work (same thing as saying it's a half wavelength).

    Fellow hams, we have to be careful. There is a ton of misinformation out there. In fact actual myths, things people believe that have no evidence to back them up. They get accepted as facts. I could list dozens here but we would get off track. The point is, Kevin made a video where he described an antenna he planned to build. His theory has misconceptions - they are not debatable - just plain wrong. He means well but he doesn't understand fundamentals. Yet people pile on with congratulations for experimenting, "Oh, great job, looking forward to more videos, experimenting is the foundation of amateur radio, blah, blah"
    Any rf engineer, antenna engineer would look at this video and laugh. Folks, this is why people criticize us and use terms like dumbing down, and getting your license from a cracker jack box.
    KR3DX, AB7E and K4AGO like this.
  2. KQ6XA

    KQ6XA Ham Member QRZ Page

    "Using a transmission line as an antenna" has been around for a while.

    Even coaxial lines can be utilized as an antenna.

    Yes, there are ways to end-feed a section of high impedance open wire balanced feedline as a very efficient antenna.

    My friends, please consider the lowly small loop antenna.
    The small loop antenna might be technically described as a balanced transmission line that is shorted on both ends!
    ... or one end, depending on how it is set up.

    Impedance is a virtue.
    Last edited: Jul 9, 2019
  3. AJ4GQ

    AJ4GQ Ham Member QRZ Page

    And, apparently, ignorance is bliss.
  4. N1BCG

    N1BCG Ham Member QRZ Page

    Are you disputing that experimenting is the foundation of amateur radio?

    History is not on your side.
  5. W6PEP

    W6PEP Ham Member QRZ Page

    A dipole that is end fed and folded is not a dipole. A flute with no holes is not a flute. But if software says it will work??
    KA2FIR likes this.
  6. K2XT

    K2XT Premium Subscriber QRZ Page

    Oh come on, now. I'm saying what he is doing is not experimenting. He's feeding a shorted line with 49:1 stepDOWN transformer. That's not experimenting unless he wants to see how much transmitter power it takes to blow up the ferrite balun, or un-un! Or his finals.
    AB7E, K4AGO and N1BCG like this.
  7. AA7EJ

    AA7EJ Ham Member QRZ Page

    Here is something puzzling me - of course it is OT and may get be banned.
    Up front , and I have stated this many times - I have no illusions what is the purpose of this site.

    Post in "Amateur radio news " has to be blessed by administrators.
    Apparently the virtue of the "experiment" post falls in with the purpose of the forum.

    Forum administrators are actively involved in preventing scammers to defraud the less aware forum participants
    buying and selling their ware.
    And I foolishly though that only government "is here to help ".

    Yes, amateur radio is still fascinating hobby , irregardless.

    73 Shirley

    Small loops have a nickname - magnetic loop. Never heard of term "magnetic diploe". Wonder why.
  8. KL7CY

    KL7CY Premium Subscriber QRZ Page

    I believe the currents in either side of the twin lead will be out of phase. This will cause cancellation of any radiated energy. It might make a good dummy load...
  9. K2XT

    K2XT Premium Subscriber QRZ Page

    Nope, won't even make a good dummy load. In fact it is the worst load you could have for your transmitter, a short circuit with a matching transformer in between that is trying to step DOWN the (theoretical) zero ohms impedance.
    The only question is, which will fail first, the transmitter or the unun (matching coil). It's ridiculous.
    K4AGO likes this.
  10. AB2RA

    AB2RA Ham Member QRZ Page

    "I am not sure the impedance, but a 1/4 wave folded monopole has an impedance of 150 ohms and has been in use at vhf and uhf as a base station antenna since at least my 1968 ARRL handbook. - WA3YRE"
    WA3YRE is correct that a 1/4 wave folded monopole would work, but the half wave will not.
    The Bill Orr Radio Handbooks of the 50s and 60s show a 1/4 wave antenna like this for HF,
    which is what the author is trying to do the wrong way.
    The advantage of the folded arrangement is that the impedance is higher, possibly mitigating the ground loss.
    I would encourage the author to give this 1/4 wave configuration a try.
    If you cannot erect it at full height, the top portion can be horizontal, like an L antenna, and still be useful.
    A variation is also show in Orr's work, the "Multee", a two band version, which fits on a city lot.
    Its performance, if properly installed, can be better than similar sized compromise antennas.
    The purpose of amateur radio includes experimentation. Don't bash the newbies when they are curious; offer them help.
    When experimenting, it is wise to read up on the existing information, to avoid reinventing the wheel.
    In this case, a square wheel. A cautionary tale.
    73, AB2RA
    KA2FIR likes this.

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