Feeding EFHW Vertical antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by VK4WTN, Apr 4, 2021.

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  1. VK4WTN

    VK4WTN Ham Member QRZ Page

    hi all I am going to build an efhw vertical antenna for 20M and was wondering the best way to feed it.There seems to be two popular ways. A 49:1 toroid broadband toroid or a two turn primary coupled to a resonant tuned circuit. I wonder if there is much difference in efficiency between these two feed methods? I also plan to use a choke on the feedpoint to stop common mode current and most likely a .05 wavelength counterpoise.
    Thanks Wayne VK4WTN
     
  2. KU3X

    KU3X Ham Member QRZ Page

    The actual best way to feed it is with a 1/4 wave of 450 ohm transmission line. But, by doing so it becomes a mono band vertical.

    Barry, KU3X
     
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  3. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    I can't tell you how to feed it, but keep the fed end elevated! If you can get it up to 10m I think you will pleased with that antenna.

    I look forward to working you.
     
    KU3X likes this.
  4. VK4WTN

    VK4WTN Ham Member QRZ Page

    Thanks for the replies guys
     
  5. M0AGP

    M0AGP Ham Member QRZ Page

  6. M0AGP

    M0AGP Ham Member QRZ Page

    AK5B likes this.
  7. AA3EE

    AA3EE Ham Member QRZ Page

    Look for a Sept. 2005 QST article by K6MHE called "A 20 and 40 meter vertical on autopilot". It describes a matching network to use a 33' vertical on both bands. It's a traditional vertical with ground wires though.
     
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    Wayne,

    Build both. Call them A an B.

    Put A in a old picnic cooler and measure the initial temperature inside the cooler. Connect A to antenna and transmit at 1000W key-down cw for 60 sec. Make sure the cooler lid seals properly with the coaxes entering/leaving the cooler. Measure the temperature rise inside the cooler after the transmission.

    After letting the cooler return to ambient temperature, put B in the cooler and repeat the experiment. The more rapid the temperature rise during key down, the more loss in the network...

    The advantage of the ferrite transformer is that it works over at least a 1:8 frequency span. The air-core tapped, tuned transformer has a high Q, and may need re-tuning even when spanning a single band.

    You can create the required 0.05wl counterpoise just by moving the Coax Common Mode Choke a few feet away from the transformer.

    The alternative counterpoise for a half-wavelength vertical is to drive a single ground rod into the earth and then connect the ground-end of the ferrite/tuned transformer and the coax shield to the ground rod. Because the current into the ground rod is tiny (compared to what it would be if the monopole is 1/4wl), then the ground loss is tiny....
     
    Last edited: Apr 4, 2021
  9. VK4WTN

    VK4WTN Ham Member QRZ Page

    Thanks for the replies everyone. Most likely will try both the 49:1 transformer and the tuned transformer and compare them. I am also going to add switching so the matcher can be bypasses and use the 10M of wire on 40M as a quarterwave with additional counterpoise. It would be interesting if several half wave wires can be paralleled at the bottom and fed to the 49:1 transformer similar to the dx commander. Now that would be interesting for a multiband antenna
     
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  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    Not that I can see... In a "fan" dipole, or "fan" vertical, the lowest parallel impedance wire takes all of the current. Since end-fed half-wave wires are each a super-high impedance, you would have to wire them in series (instead of parallel, like the fan) to accomplish the automatic "band switching"!
     
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