Hf vertical without radials

Discussion in 'Ham Radio Discussions' started by KG5PNI, Jun 19, 2019.

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  1. WR2E

    WR2E Ham Member QRZ Page

    Maybe there were no iota's on the air then?

    But seriously... I could never hear a whole lotta difference on receive myself between my doublet and my 1/4w elevated vertical.

    The vertical seemed to make an 'edge' of difference on transmit though but only on DX, and just an edge, on the A/B comparisons that were done at the time.
     
    KA4DPO likes this.
  2. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    Most hams are ignorant about antenna theory, ground loss, and loading effects of poor ground so they are happy with almost anything as long as it returns a one to one SWR. Most hams also equate SWR with efficiency again, because they have no idea about the difference between electrical ground and RF ground.

    What part of "they recommend a minimum of 16 radials" did you not get. That came from the manufacturer, not me. The word minimum implies that more is better, and it is. I have science on my side.
     
    NL7W, K8XG and KC8VWM like this.
  3. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    Elevated verticals are almost always far more efficient than ground mounted verticals. Only three quarter wave radials are needed to achieve 90% counterpoise efficiency on an elevated vertical.
     
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  4. WR2E

    WR2E Ham Member QRZ Page

    I used four on mine, elevated about 10'.

    That's what I attributed the minor difference between the two antennas to. I've not compared a ground mounted with a good radial field to the doublet. Might see bigger differences there...
     
  5. WR2E

    WR2E Ham Member QRZ Page

    I've often wondered why the big differences. Parts of the heartland up at 30. I know it's gotta be the soil or geology but never found the time to investigate the WHY. Maybe they got a big splash of some ejecta from Chixaloob?
     
    KA4DPO likes this.
  6. WF7A

    WF7A Subscriber QRZ Page

    It figures: Where I live, it's '1' on the chart.
     
    KA4DPO likes this.
  7. K3EY

    K3EY XML Subscriber QRZ Page

    Verticals equal noise noise and noisier and why no longer use them.
     
  8. K4KYV

    K4KYV Subscriber QRZ Page

    The qualifier is "ground mounted". An elevated vertical radiator, essentially a full-length or shortened resonant vertical dipole may work well. WWV used them back when they were on the east coast, vertical half-wave dipoles mounted on wooden poles with stand-off insulators. I'm not sure about the present-day Colorado location.

    The closer the vertical radiator is to the ground, the more the ground loss, as more of the displacement current from the vertical radiator attempts to return to the common point at the base of the antenna via the lossy earth. This is why with a vertical antenna, a few elevated radials may work as well as a large number of radials lying on the ground or buried in the soil.

    Take the classic quarter-wave ground plane. On 2m or 11m cee-bee, a quarter-wave vertical radiator with the base and ground plane a substantial fraction of a wavelength, or several wavelengths, above ground works just fine with only 3 or 4 radials. But a quarter-wave vertical with the base right on the ground works very poorly without a relatively large number of radials. It follows that at intermediate points between zero and a substantial fraction of a wavelength, the higher the antenna base/ground plane from the earth, the fewer radials needed.

    The ground plane serves as the "missing half" of the quarter-wave vertical. If it is raised high enough, the ground plane could be replaced by another quarter-wave vertical section, turning it into a vertical centre-fed dipole. But even then, the bottom end must be separated by some distance from the earth or else ground radials must be installed; otherwise the lossy earth will capture some of the displacement current and convert it to heat as wasted power.

    That's the fallacy of the "no-radials" half-wave vertical. Sure, it radiates some RF and may even appear to perform well as a DX antenna, but still, 50% to 80% of the transmitter power may be wasted warming earthworms instead of radiating into space. Some AM broadcast vertical towers are a half wave or more in length, but they always include an extensive radial system. If the radial system weren't necessary, they would simply erect a tall vertical tower and not spend tons of money on real estate and copper wire to build the radial system.

    As a matter of semantics, another way of looking at it, one may think of the radial system as a Faraday shield isolating the bottom end of the vertical radiator from the lossy earth. The radials effectively short-circuit the ground resistance, and detour the captured return currents back to the base through copper wire instead of through lossy soil minerals. The closer the vertical radiator to the lossy earth, the more complete this "shield" needs to be to keep the RF currents away from the soil. In the case of a half-wave vertical high enough above the ground, most of the antenna current returns directly to the opposite end of the radiator as displacement current with very little captured by the soil, exactly as in the case of a horizontal half-wave dipole.

    A self-resonant end-fed long wire may not need a counterpoise system. A classic example of this is the well-proven end-fed Zepp, where the antenna is some exact multiple of a half wavelength, and one of the balanced feeders connects to the end of the antenna while the other terminates into nothing except the insulator that holds it in place. If the wire is not precisely self-resonant, then a counterpoise is needed to complete the missing portion of the resonant antenna.

    Simple. Use a separate receiving antenna.
     
    K2XT, WZ7U and KC8VWM like this.
  9. KY5U

    KY5U Subscriber QRZ Page

    A vertical without radials is like a spider without legs.
     
    K4KYV likes this.
  10. K3EY

    K3EY XML Subscriber QRZ Page

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