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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. PA0MHS

    PA0MHS XML Subscriber QRZ Page

    @KB7TBT: This is just a shorted transmission line. The currents in each wire are opposite phase, thus they will cancel eachother and nothing will be radiated. If you "somehow" find a transformer that will feed both wires in-phase, you will need a ground point for the other end of the transformer. And at that point, you re-created the end-fed dipole again because two wires close to each other, having the same current phase, are the same as one wire.
     
    K4AGO, G8FYK and K2XT like this.
  2. N8WUR

    N8WUR Ham Member QRZ Page

    Of course, it's possible to use the correct terminology, but you are not! The center fed antenna you refer is sometimes referred to as a "doublet", and it is one of many types of true dipoles. But not all dipoles are doublets. Any half-wave radiator with the ends not connected to each other is a dipole. The term refers not to the connection method but to the current distibution. The current is distributed along its length so that the current is maximum at the center and at opposite polarity at opposite sides of the center, regardless of where is the feed point. Therefore, the origin of the term, "dipole", meaning, "of two polarities" The dipole can be fed anywhere along its length and these conditions will not change. The feed system can be attached anywhere or not attatch ed at all(parasitic feed). A solid piece of wire, rod, or tubing, fed anywhere, bent into any shape, and mounted in any position, is still a dipole. The only thing that is changed by moving the feed point along the dipole is the apparent feed point impedance. The "windom" antenna to which many people refer is actually an off-center-fed dipole. The true windom is a vertical wire antenna using a half wave piece of wire as a top capacitance hat and as a support wire. The only (minor) radiation from the horizontal section is that caused by the slight unbalance introduced by the off-center attachment. The"j-pole" and half wave "zepp" are both classic (and identical) examples of quarter--wave-section matched end fed dipoles. It's all in the books as stated. The books I highly recommend are the ARRL Antenna Book and Walt Maxwell's "and

    Respectfully, N8WUR
     
    K4AGO, PA0MHS and KG5KPU like this.
  3. N8WUR

    N8WUR Ham Member QRZ Page

    Hmmmm, seem to have an error n my earlier post. The title of Walt Maxwell's book is "Reflections", any edition, and it deals thoroughly and correctly with transmission lines and matching. Edition 3 is available from CQ publishing and is well worth the purchase.

    Respectfully, N8WUR
     
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  4. KG5KPU

    KG5KPU XML Subscriber QRZ Page

    I was under the impression that a Windom is fed against ground, and uses a single-wire feeder, not coax. Any variation of an "off-center fed" antenna would not, per my understanding, be, as you say, "in fact, a Windom." There are variants of the Windom known as the Carolina Windom that resemble an OCF, but they use a tuning stub with a choke as part of the feeder (which is coax). The OCF "dipole" I have uses a 4:1 current balun, but does not use a specific length of coax as any sort on intentional radiating stub.

    Also, I am under the impression that a there are more variants to the end fed than you allow...an end fed does not have to be one or the other -random or longwire. There is also the end-fed half wave, which is a specific length and cut to a half wave, using a 49:1 transformer; it is neither a random or long wire. There is also the Inverted L.

    Aside from that, I do agree...I am not a fan of the term "end-fed dipole."
     
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  5. K2XT

    K2XT Premium Subscriber QRZ Page

    With all due respect to Artie Johnson, "Veddy in-ter-esting."
    You are saying the vertical wire isn't really a single wire feedline for a halfwave antenna, but rather a Marconi-style vertical antenna with an unsymmetrical top section? Hmmmmmm....... we just might have to put this into 4NEC2 and take a look.
    Now we are getting somewhere as far as experimenting, and possibly learning something, right N1BCG?
     
  6. VE3VXO

    VE3VXO Ham Member QRZ Page

  7. AI3V

    AI3V Ham Member QRZ Page

    Because the terms "magnetic loop" and "end fed antenna" are unique to sammy hammys, and not used by real antenna engineers.

    Rege
     
  8. KX4O

    KX4O Ham Member QRZ Page

    Oh I don't know Rege... I'm a real antenna engineer and I use the similar term end-fed dipole. Oh I know it isn't quite at the end, but is certainly close enough for all practical purposes.

    I don't use magnetic loop though. STL is more like it.
     
  9. KB0R

    KB0R Premium Subscriber QRZ Page

    W
    Will you accept "End Fed Zepp"?
     
  10. AI3V

    AI3V Ham Member QRZ Page

    Whatever you say.

    Rege
     

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