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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Topband Reflector
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