Zepp, exteded Zepp, double extended Zepp?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AA7EJ, May 19, 2016.

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  1. K9STH

    K9STH Ham Member QRZ Page

    EJ:

    Not exactly!

    A true Zepp is a half-wave, at the lowest frequency, end fed antenna fed with balanced line a quarter-wave in length. One side is connected to the half-wave wire and the other side is not connected at the antenna end.

    Any other feed arrangement removes the antenna from the "true" Zepp configuration.

    Glen, K9STH
     
  2. AA7EJ

    AA7EJ Ham Member QRZ Page

    I am still not convinced that adding 1/4 wavelength impedance matching transformer makes "true Zepp".

    Actually the goal is to match the (high impedance) radiator to (50 /70 Ohms) feed line and in that case 5/8 wavelength long radiator would give better results to match to 450 ohms ladder line since the impedance would be much leas than at the end of the 1/2 wavelength radiator.
    This is well known case due to an extensive experimentation with another (1/2 wavelength ) dipole fed off center - Windom.

    There are also "Zepps" designs with 9:1 (impedance matching) balun located at the end of the antenna and terminated into ( random lenght) coax feed line.

    A 1/4 wavelength balanced feed line still should be "converted" to unballanced TX PA circuit, just to be picky.


    Also to agree with "1/4 wavelength matching stub is part of radiator" we would have to call coiled coax choke on plain dipole feed point "part of the radiator " too. Which we do not, because it is not a radiator.
     
  3. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Incidentally, it took me a while to figure out why the Germans wanted an antenna that would be current fed for their airships - after all, it's convenient for us today, with our 50 ohm equipment, but most transmitters world-wide in the '20s used direct matching off the tank coil, and were usually tapped high on the coil and voltage fed.

    I think the Zeppelin designers must have wanted a nice low voltage point at the feedthrough terminals to avoid the chance of arcing across the terminals on the Zeppelin's skin. Arc + Hydrogen gas = "Oh, the humanity!"
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Hindenberg.

    My take is I don't care what any antenna is called, the only thing that matters is how it works.

    I call my homebrew antennas 'Arthur.' That's from an old Beatles movie, when a reporter asked George Harrison what he calls his haircut.

    Problem with any straight wire antenna that's longer than a wavelength is its radiation properties become so weird I wouldn't want to use one for anything.
     
  5. K9STH

    K9STH Ham Member QRZ Page

    EJ:

    Yes, it does! That is because the Zeppelin antennas were designed as such. That is, a quarter-wave, at the lowest frequency balanced feed line with a half-wave antenna attached. You can change any part of the antenna that you want. However, any changes, in design, removes it from the original and, as such, it is no longer "true" to the original, design. Therefore, anything but the original design is NOT a "true" Zepp!

    Also, only with "modern", 50-ohm fixed impedance, transmitters must the impedance be "converted" to unbalanced. There are a LOT of older transmitters, even with Pi-networks, that can easily match the feed line. I used my 160-meter Zepp with first, a WRL Globe Chief 90A that could "match" impedances at least as high as 1200-ohms and with my original Heath DX-100 that could "match" impedances at least as high as 300-ohms. The side, of the feedline, that was attached to the antenna was connected to the center of the SO-239 on the DX-100 and to the binding post on the Globe Chief 90A that went to the "high" side of the Pi-network. The "other" side of the feed line was connected to the chassis.

    This was done, by most operators, in the "goode olde days" with the 300-ohm balanced feed line for feeding folded-dipole antennas. Very few bothered with things like balun coils although such were definitely available including the Heath B-1 that was available between 1957 and 1963.

    Glen, K9STH
     
    KC8VWM likes this.
  6. AA7EJ

    AA7EJ Ham Member QRZ Page

    OK , we should agree to disagree. No problema.

    Since the true reason for end fed antenna was bought up by YUZ, kudos. .

    Here is another example of similar setup.
    I have observed on B-17 - "Texas raiders" - its "trailing antenna".
    It was / is SINGLE wire for the same reason - connected to ARC 5 tube TX high impedance output.
    I wonder why the American engineers omitted the balanced line?
    Maybe shortage of war material?

    But we got educated on feeding folded dipole, so no big loss.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    With a tube power amplifier, feeding a high-Z load is pretty easy and may take fewer parts if the TX is designed for that. Very little current at the output terminals, all you need is enough insulation.:)
     
  8. K9STH

    K9STH Ham Member QRZ Page

    EJ:

    The B-17 doesn't have any hydrogen involved in the aircraft design which, if ignited, could prove to be a disaster. With all of the hydrogen airships, it was necessary to do everything possible to prevent any sparks, or open flames, which could easily ignite any hydrogen that happened to escape from the gas bags.

    During the 1920s, well into the 1960s, many aircraft, for HF operation, employed trailing wire antennas which were "end fed". TACAMO aircraft, which are used in communications with submerged submarines, still employ end-fed trailing wire antennas.

    As WIK pointed out, especially with tube type transmitters, it is very easy to obtain a "match" to the impedance presented by the end fed antenna without worrying about matching a balanced impedance that, in turn, would add to the cost of the system. When the total number of aircraft is taken into consideration, which, during World War II alone, was in the hundreds of thousands for the Allies, the savings would definitely been in the tens of millions of dollars.

    Glen, K9STH
     
    KA0GKT likes this.
  9. AA7EJ

    AA7EJ Ham Member QRZ Page

    Which brings up back to "dipole" and understanding of its VOLTAGE distribution indeed.
    But since end fed Zepp is NOT a dipole, as we are lead to believe, no worries , hydrogen or no hydrogen.

    73
    ..._._ ..
     
  10. KC8VWM

    KC8VWM Ham Member QRZ Page

    Who was ever led to believe an End Fed Zepp antenna is a dipole?
     

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