The End Fed Half Wave.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by M6LVC, Aug 9, 2020.

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  1. M6LVC

    M6LVC Ham Member QRZ Page

    I think I understand how a dipole or 1/4 wave vertical works.
    But I’m struggling to understand how the EFHW such as the silver rod type CB antennas work, does the coax act as a counterpoise, meaning the coax also radiates RF?
    I guess what I’m trying understand is why the EFHW doesn’t need Radials or something to work against?

    Many thanks in advance, Iain
     
    KX4O likes this.
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    M6LVC likes this.
  3. N1LOU

    N1LOU XML Subscriber QRZ Page

    I think you are assuming that an EFHW works as well as an antenna with radials. I would suggest, contrary to the fanboys' opinions, it does not.
     
    KD1JT likes this.
  4. M6LVC

    M6LVC Ham Member QRZ Page

    Thank you for the link, your post is very enlightening.
    Would it be correct to say that the coiled copper wire in this picture(silver rod type HWEF) acts as a matching device & counterpoise ?
     

    Attached Files:

  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    On the fundamental band, an EFHW is indistinguishable from a center-fed, half-wave dipole, provided it is installed as you would install a dipole. Since the EFHW works on twice as many harmonic bands than the CFdipole, how do you compare them on the extra bands?

    The mistake most people make with EFHWs is to treat them as a ground-referenced Marconi, with what should be a high-voltage node at the end of the "dipole" shorted to dirt (radials or ground rods). This is a gross misapplication of a dipole, regardless of where it is fed!

    The fact that you and the OP conflate an EFHW with "radials" means you do not understand the difference between a Hertz and a Marconi antenna...
     
    KK4OBI likes this.
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    As best as I can tell, the photo shows a tapped coil (air-core auto-transformer) which is typically used at the base of a 5/8 wavelength vertical. That transformer likely has an impedance step-up ratio of like 3:1. This has nothing to do with a typical near-end-fed resonant 1/2 wl dipole which uses a 1:49 impedance ratio autotransformer.

    Anybody that says that a 5/8 wl Marconi doesn't need a ground plane is fibbing...
     
    M6LVC likes this.
  7. 2E0VSS

    2E0VSS Ham Member QRZ Page

    DL2KQ Has a transformerless design for your consideration. 4 Band LW (Google translate)
    Look beyond the norm..
    It has indeed been flogged to death
    Think outside the box and less " Hamy"
     
  8. SM0GLD

    SM0GLD Ham Member QRZ Page

    If the "Silver rod" is bolted on a steel mast the mast will be acting counterpoise otherwise the coax will.
    In the base of the antenna there is a coil forming a parallel resonance together with the mounting bracket witch acts as a parallel capacitor.
    This parallel circuit is matching the antenna end impedance down to 50 ohm.

    I experimented with additional counterpoise on my silver rod to find out if it would increase the performance.
    I used a non conductive mast it didn't work at all, matching was terrible.
    Now with the 4 x 1m radials and a choke the matching is consistent and doesn't vary if you touch the coax.

    silver rod with radials.jpg
     
  9. KN6CSB

    KN6CSB Ham Member QRZ Page

    KD6RF likes this.
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    Tom's analysis is for an EFHW deployed as a Marconi (one end very close to earth, or using the earth itself as the counter poise), which in my opinion is a very poor way to deploy it. The EFHW is just another Hertzian (self-contained) dipole. It needs no counterpoise other than a few feet of coax. The goal in deploying it should be to get it as far from the earth as possible (just like a dipole)!
     

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