What's the story with end-fed antenna's?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI7QVR, Feb 27, 2018.

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  1. AI3V

    AI3V Ham Member QRZ Page

    As long as there is money to be made selling new hams "all band end fed" antennas - and the inevitable chokes,baluns,line isolators, artificial ground tuneing units, second and third vswr meters, etc,

    There will be plenty of folks keeping this argument alive.

    It's a strong fantasy, $pend a couple Grand on a radio setup, throw a wire-any wire- out the window of your apartment or HOA dream, and sit there sipping a cold 807 and having a actual conversation with someone on the other side of the world.

    Then the reality of transmitting inside the subdivision rears it's ugly head.

    My end fed does (or doesn't) do this that or the other thing? No problem, someone will be more than happy to take your money.

    Rege
     
    KD6RF likes this.
  2. W9XMT

    W9XMT Ham Member QRZ Page

    Brian's OP of this thread was not related to his "actual ability to get on the air." His post concluded with this question:

    ..."are the same losses incurred when matching a 4:1 SWR into a vertical vs. matching a 4:1 SWR into an end-fed? Please explain."
    Accurate answers to that question require more than replies advising him and other readers that a good, fact-based understanding of antenna systems is unimportant.
     
    Last edited: Mar 16, 2018
  3. W3JJW

    W3JJW Ham Member QRZ Page

    Here it is again. Everyone selling these is a thief and a liar and end fed antennas are snake oil.

    And in a thread full of end fed designs from way back, known to work, perhaps only when dipoles or other antennas won't fit, whatever the reason. Within a thread full of knowledgeable folks acknowledging they work (albeit not ideally) and have worked for years. I don't get it. Why bother posting this? I am about ready to buy Rege one of MyAntennas just to try to make him put it up or give it up.

    What I got from this thread are the following points so far:

    1. There are very likely many ways to make an "end fed" antenna using the coax braid as a return (call it counterpoise, whatever.). It is less clear to me if any of the other configurations will get RF to radiate, but not immediately obvious they won't.

    2. There are ways to set up this antenna situation where there isn't much common mode current on the return side of the current. Clearly the math is there, or Rege is ignoring it. Can this be translated to reality. It seems it can be. But it can be tricky to the point of being mysterious, and difficult or impossible to troubleshoot given the number of variables uncontrolled.

    3. There are many egos on the 'Zed.

    I wonder if standing versus traveling waves have anything to do with end fed antennas and their many mysteries....

    jay
     
    Last edited: Mar 17, 2018
    W8IXI likes this.
  4. W3JJW

    W3JJW Ham Member QRZ Page

    This fella claims to be measuring equal radiation from an end fed versus standard dipole. What's up?!



    jay
     
  5. KI4ZUQ

    KI4ZUQ Ham Member QRZ Page

  6. AI3V

    AI3V Ham Member QRZ Page

    You just don't get it Jay.

    This fellow has 2 wires connected to each of his test setup antenna.

    Iow, he has 2 different DIPOLE antenna configurations.

    THERE IS NO SUCH THING AS A END FED ANTENNA. ALL ANTENAS ARE FED IN THE CENTER. YOU MIGHT NOT KNOW WHERE "THE OTHER HALF OF THE ANTENNA" IS, BUT ITS THERE

    Rege
     
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    This is a (blatantly wrong) personal opinion, not supported by science.
     
  8. W9XMT

    W9XMT Ham Member QRZ Page

    Suggested changes to make these quotes from AI3V in Reply 196 more acceptable:

    Delete"... ALL ANTENAS ARE FED IN THE CENTER."
    Reason: A dipole can be fed off-center, and still be an efficient radiator.

    RE: "YOU MIGHT NOT KNOW WHERE "THE OTHER HALF OF THE ANTENNA" IS, BUT ITS THERE.
    Change to: You might not know what comprises the 2nd radiating section of an "EFHW" antenna, but its there.
     
    Last edited: Mar 18, 2018
    WA7ARK likes this.
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    1. Not knowing where the other half of the antenna is applies to a center-fed 1/2 wavelength dipole if the feed-line is coax, and there is nothing on the outside of the coax to block common-mode current. Only if the antenna ends are perfectly balanced (equidistant) with respect to earth, the feedline comes off the dipole at right-angles to the dipole, and if the feedline is twin-lead might you make the case that a common-mode choke is not required, and that the feedline does not become part of the antenna. Case 1 is the average ham dipole.

    2. Offsetting the feed-point right or left of center changes the feed-point impedance, but doesn't materially change the current distribution along the 1/2 wavelength wire, provided that the common-mode current path along the feedline is adequately blocked. This becomes progressively harder to do as the feedpoint moves further from the center because now the feedline is asymmetric with respect to the near fields around the radiating wire. It might take multiple common-mode chokes spaced along the feedline to suppress the common-mode current in the feedline. It would be harder to do so if the feedline is coax; not twin-lead. Case 2 is a 33% offset OCF multiband dipole like the Buckmaster.

    3. Carrying case 2 to its logical conclusion, move the feedpoint to within a few % of the 1/2wavelength wire end. The feed impedance goes higher, and becomes reactive, but you can still establish almost the same current distribution on the wire as in case 1 or case 2, but as you get closer to the wire end, the common-mode current on the feedline gets even harder to suppress. The closer you get to the end of the 1/2wavelength wire, the higher the feed impedance. Case 3 is an extreme version of an OCF dipole, used to add more bands to a multiband OCF.

    4. Move the feedpoint all the way to the end of the 1/2wavelength wire, using coax feed, with no attempt at eliminating common-mode current on the coax, using a step-up transformer connected as an autotransformer (no isolation from primary to secondary windings). Now you have an antenna that is much longer than 1/2wavelength, one part is the original 1/2wavelength dipole wire, while the rest is the radiation from the outside of the coax, however long that is, and however it is routed. The common-mode current on the coax is less than you would expect, because it only has to balance the rather small current at the end of the halfwave wire. Case 4 is what is marketed as an EFHW.

    So, there is no mystery of "WHERE THE OTHER HALF OF THE ANTENNA IS"!
     
    Last edited: Mar 18, 2018
    W3JJW likes this.
  10. KI7QVR

    KI7QVR Ham Member QRZ Page

    Wow...I really didn't think my original post would pick up this much steam. There's a lot of good stuff to took at and consider but the PDF about feed lines was particularly interesting.

    I thing I need to dig into my Antenna Handbook...Thanks for all the replies and great info.
     

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