Topband: 5/8 wavelength vertical is mo betta than shorter versions??
Charlie Cunningham
charlie-cunningham at nc.rr.com
Sat Sep 7 20:00:48 EDT 2013
Hi, Jim!
Good to hear from you!
I don't think there's any simple or definitive answer to your question. The reason is that the 5/8 wave vertical splits the radiation into 2 lobes and has a second higher angle lobe, compared to a 1/4 wave monopole. Sometimes, depending on distance (and skip distance), time of day, frequency, trans-equatorial propagation etc. the high angle lobe can add some advantage. A similar situation exists sometimes at VHF/UHF in mountainous areas with mountain top repeaters, Sometimes the high angle lobe can help out the mobiles at lower elevations. Similarly, the mountaintop repeater is better using a 1/4 wave or 1/2 wave vertical than 3 or 5 half-waves in phase that have gain toward the far horizon, but put less signal down into the valleys and hear less well at lower elevation angles. So no simple answers. But, after all, we can't reason people out of firmly beliefs that they didn't arrive at through reason! :-)
BTW - how's your KAZ terminated loop doing??
Regards,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of James Rodenkirch
Sent: Saturday, September 07, 2013 7:25 PM
To: topband at contesting.com
Subject: Topband: 5/8 wavelength vertical is mo betta than shorter versions??
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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