Topband: 5/8 wavelength vertical is mo betta than shorter versions??
James Rodenkirch
rodenkirch_llc at msn.com
Sat Sep 7 19:24:45 EDT 2013
I saw someone post a "my 5/8 wavelength vertical really outperformed my 1/4 wavelength vertical" a day or two ago.
I kinda wondered about that (I've "heard" a 5/8 wavelength is mo betta) so I did a little digging around.
From a K3LC paper on tall verticals - http://www.arrl.org/files/file/QEX_Next_Issue/May-Jun_2011/QEX_5_11_Christman.pdf - I found the below:
Performance comparison between vertical antenna systems of varying height, when operating on 80 meters at a frequency of 3650 kHz. The monopoles are made from no. 10 AWG wire, with a ground screen composed of 60 buried no. 14 AWG radials (radial length = monopole height). All conductors are aluminum, and the soil is “average” (conductivity = 0.005 siemens/meter and dielectric constant = 13).
¼ λ System 3⁄8 λ System ½ λ System 5⁄8 λ SystemMonopole Height and Radial Length (ft) 67.368 101.05 134.74 168.42Input Impedance (Ω) 41.4 + j 24.4 229 + j 605 2324 – j 1425 86.1 – j 479SWR (50 Ω ref.) 1.75 36.8 64.0 55.5Peak Gain (dBi) and Take-off Angle (°)0.39 at 24.7 0.79 at 21.7 0.96 at 17.6 0.42 at 13.3Gain (dBi) at 5° Take-off Angle–5.21 –4.34 –3.42 –2.81Gain (dBi) at 10° Take-off Angle –1.70 –0.91 –0.14 0.06Gain (dBi) at 15° Take-off Angle –0.32 0.35 0.85 0.34Gain (dBi) at 20o Take-off Angle 0.25 0.76 0.89 –0.63Half Power Beamwidth (°) 43.7 38.0 29.0 20.3Efficiency (%) 33.8 34.3 29.6 29.8
Performance comparison between vertical antenna systems of varying height, when operating on 40 meters at a frequency of 7150 kHz.
The monopoles are made from no. 10 AWG wire, with a ground screen composed of 60 buried no. 14 AWG radials (radial length =monopole height). All conductors are aluminum, and the soil is “average” (conductivity = 0.005 siemens/meter and dielectric constant = 13).
¼ λ System 3⁄8 λ System ½ λ System 5⁄8 λ SystemMonopole Height and Radial Length (ft) 34.391 51.586 68.781 85.976Input Impedance (Ω) 39.9 + j 25.0 235 + j 570 1937 – j 1247 81.9 – j 436SWR (50 Ω ref.) 1.81 32.5 54.8 48.7Peak Gain (dBi) and Take-off Angle (°) 0.15 at 26.2 0.68 at 23.3 0.89 at 19.1 0.68 at 14.5Gain (dBi) at 5° Take-off Angle–6.15 –5.15 –4.13 –3.12Gain (dBi) at 10° Take-off Angle –2.38 –1.44 –0.56 0.08Gain (dBi) at 15° Take-off Angle –0.82 0.02 0.66 0.67Gain (dBi) at 20° Take-off Angle –0.11 0.59 0.88 0.04Half Power Beamwidth (°) 44.1 39.3 30.7 22.3Efficiency (%) 31.9 34.0 30.4 31.7
Performance comparison between vertical antenna systems of varying height, when operating on 20 meters at a frequency of14.175 MHz. The monopoles are made from no. 10 AWG wire, with a ground screen composed of 60 buried no. 14 AWG radials (radial length = monopole height). All conductors are aluminum, and the soil is “average” (conductivity = 0.005 siemens/meter and dielectric constant = 13).
¼ λ System 3⁄8 λ System ½ λ System 5⁄8 λ SystemMonopole Height and Radial Length (ft) 17.347 26.020 34.694 43.367Input Impedance (Ω) 39.0 + j28.4 247 + j536 1595 – j1070 77.4 – j392SWR (50 Ω ref.) 1.97 28.3 46.3 41.8Peak Gain (dBi) and Take-off Angle (°) 0.29 at 27.1 0.91 at 24.3 1.16 at 19.9 1.21 at 15.0Gain (dBi) at 5° Take-off Angle –6.35 –5.28 –4.18 –2.86Gain (dBi) at 10° Take-off Angle –2.46 –1.45 –0.49 0.48Gain (dBi) at 15° Take-off Angle –0.8 1 0.1 1 0.84 1.21Gain (dBi) at 20° Take-off Angle –0.04 0.76 1.16 0.70Half Power Beamwidth (°) 44.4 40.4 31.5 22.8Efficiency (%) 32.9 36.3 32.9 34.7
The above modeling results just don't support that contention/posit so I'm wondering what else comes in to play that could lead folks to love the 5/8 wavelength vertical over a shorter version, regardless of frequency? I don't see one performance comparison that supports that claim. I'm not saying the "claiming person" isn't correct but....I don't see how!
Help - what am I missing here?
72, Jim Rodenkirch K9JWV
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