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

    If you don't understand basic antenna/transmission line theory but you make a video of it, and QRZ features it on the home page you get a lot of views and spreading of misinformation.
    It's a simple 1/2 wavelength of transmission line. The feedpoint impedance is the same as the far end, a short.
    Trying to feed a short with a high impedance transformer?
    This video either should be removed or a warning in the title that this is 180 degrees out of phase with antenna fundamentals.
     
    KR3DX, AB7E, KA2FIR and 2 others like this.
  2. KG6BXW

    KG6BXW Ham Member QRZ Page

    Ham radio is about experimentation and that's what this video is, a video series on an experiment. He isn't spreading misinformation, he isn't even claiming anything. The first half of the video is just him saying "no idea if this will work why not try it". It's a good educational example of how to think about designing an antenna. Hopefully, he'll make a video explaining what worked and didn't work so others can learn.
     
  3. N1BCG

    N1BCG Ham Member QRZ Page

    It's good to experiment
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    (Couldn't help it)
     
    Last edited: Jul 8, 2019
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  4. KX4O

    KX4O Ham Member QRZ Page

    By definition a dipole is defined by function and having no greater than two current nodes with no regard whatsoever to location of the feed point.

    From IEEE-100-1984 - ANSI/IEEE Std 100-1984 IEEE Standard Dictionary of Electrical and Electronics Terms
    dipole antenna (antennas). Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole.
    NOTE:Common usage considers the dipole antenna to be a metal radiating structure which supports a line current distribution similar to that of a thin straight wire so energized that the current has a node only at each end. Syn: doublet antenna.“​

    From IEEE-145-1993 - ANSI/IEEE Std 145-1993 IEEE Standard Definitions of Terms for Antennas
    dipole antenna (antennas). Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole. Syn: doublet antenna.
    NOTE: Common usage considers the dipole antenna to be a metal radiating structure which supports a line current distribution similar to that of a thin straight wire so energized that the current has a node only at each end."​

    From EIA/TIA-329-B - ANSI/EIA/TIA-329-B-1999 Minimum Standards for Communication Antennas.
    Half-Wave Dipole Antenna. A dipole whose electrical length is half a wavelength and is formed by a straight metallic radiator, one-half wavelength long, whose diameter is small compared to its length, so energized that the current has two nodes, one at each end, producing maximum radiation in the plane normal to its axis."​

    Yes.
     
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  5. K7MYR

    K7MYR Ham Member QRZ Page

    I tend to agree.

    I am inclined to NOT "beat him up" for doing what most would call "experimenting". That's how all of us learn......

    Now, If he arrives at the wrong conclusion, there will be no shortage of people here to set him straight...........(gently or otherwise)
     
    K4AGO, K8AI, N1BCG and 2 others like this.
  6. N1BCG

    N1BCG Ham Member QRZ Page

    But seriously, to TBT, experimentation is the foundation and very essence of amateur radio so no one should discourage that, although posting a video (compared to posting a comment) will ratchet up the stakes, perhaps higher than necessary.
     
  7. K2XT

    K2XT Premium Subscriber QRZ Page

    You could learn ten times as much by looking up a shorted half wave transmission line in any antenna book in the last 100 years and realizing what it is, and it isn't an antenna. He has a vna. Let him show the real characteristics of a shorted line, then the viewer will learn something. But calling it an antenna, or experimenting? no, sorry, can't agree.

    Say you ran a transmission line out your window to a dummy load in the yard, would you call that an antenna? Would you call it experimenting? No? Ok, then, replace the dummy load with a short circuit. Now are you experimenting, and expecting it is going to magically become a half wave end fed folded dipole super duper antenna? No, it is not.
     
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  8. G8FYK

    G8FYK Ham Member QRZ Page

    This makes a good topic for an "April Fool's" joke. Nothing more, nothing less. Reminds me a bit too much of the old one about transmitting into two six inch nails, but fed by 132 feet of balanced line feeder !!
     
    K2XT likes this.
  9. WA3YRE

    WA3YRE Ham Member QRZ Page

    An end-fed is generally called a marconi. To be a longwire it must be multiple wavelengths long at the frequency of operation, thus an end fed wire worked against ground that is 122 feet long is not a longwire on 75 meters, but it would be considered a longwire on 10 meters.

    I am pretty fed up with folks not using the proper names for things. The only possible end fed dipole is a coax or sleeve dipole, but of course the feed point is still in the center, the feedline just happens to go down the center of one dipole element.

    What this fellow has is a 1/2 wave folded monopole. He will need matching. I am not sure the impedence, but a 1/4 wave folded monopole has an impedence of 150 ohms and has been in use at vhf and uhf as a base station antenna since at least my 1968 ARRL handbook.

    It is sad that those who are inexperienced and do not know any better will take a video like this as truth and start calling things end feed folded dipoles.

    Should we start a go-fund-me page to purchase a clue for this fellow, or maybe a good collection of theory books?
     
    K2XT likes this.
  10. AA7EJ

    AA7EJ Ham Member QRZ Page

    Experimenting is mostly a good thing.
    ( Unless in involves puberty or "controlled substance "' )

    But it helps to have some idea about the validity of an experiment.
    Would you "experiment" in putting 10 pounds of potatoes into five pound bag?
    Probably not.

    But it seems to be accepted by this crowd to present this "fooled diploe experiment" without apparent knowledge of the size of the potato bag.

    73 Shirley
     
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