contesting with verticals & vdas - va3cco.com · it has rejection of out-of-band signals due to...
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January 2015 Copyright 2015
Contesting with Verticals & VDAs
Pete VE3IKV / VA3RA / VP2EAT
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Contesting with Verticals & VDAs
• “Verticals” means both gain-type HF monoband verticals and vertical directional arrays (VDAs)
• Object is to keep the main vertical radiation pattern as low as possible (<10 degrees) in order to maximize F2 signal propagation & signal strengths
• Simple trap yagis, spiderbeams, etc. low to the ground have a much higher radiation angle, and therefore substantially less gain below 10 degrees
• Simple monoband VDAs can also provide additional gain, and an even lower radiation pattern when near salt water, or when elevated with a clear horizon
• Omnidirectional pattern (or hemispheric pattern with VDAs) may be useful during contests, since a rotor is not necessary
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• What is a “gain” monoband vertical?
• When properly matched with a low-loss network at the base, and using an extended 0.64 wavelength radiating element, and four 0.67 wavelength radials sloping at 45o, the monoband vertical will have:
approximately 5dBi omnidirectional gain
a low vertical radiation angle of approximately 8 degrees above the horizon
a 50-ohm source impedance with low VSWR
• A matching network of 5/16” copper refrigeration tubing wound on a section of 4” diameter plastic septic drainage pipe makes a very low-loss matching network
Contesting with Verticals & VDAs
Gain Monoband Verticals
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Contesting with Verticals & VDAs
• 0.64 wavelength produces the maximum gain before the radiation pattern begins fracturing into multiple lobes (2x = old “extended double zepp”)
• The 0.64 wavelength “gain vertical” open-coil tapped matching network is inherently grounded, so as a result the antenna exhibits:
very low noise,
the VSWR is not affected by rain, and
it has rejection of out-of-band signals due to the tapped matching coil design
voltage maxima is at a higher physical height than a ¼ wave vertical (a 10m 0.64 wavelength radiator = 22 feet vs. 10m ¼ wave = 8.2 feet) – less RFI at rig as a result
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January 2015 Copyright 2015
Contesting with Verticals & VDAs
Monoband 0.64 + 0.67 WL radials vertical pattern
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January 2015 Copyright 2015
Contesting with Verticals & VDAs
10m 0.64 WL monoband gain vertical at VP2EAT
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January 2015 Copyright 2015
Contesting with Verticals & VDAs
10m 0.64 WL monoband gain vertical at PJ7/VA3RA
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January 2015 Copyright 2015
Contesting with Verticals & VDAs
10m 0.64 WL monoband gain vertical at FJ/VA3RA
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Contesting with Verticals & VDAs
Year 1: Results using a 10m monoband 0.64 lambda gain vertical:
2011 – TOP CQ WW DX CW SOSB/10 LP
• 9J3A...........1,403,506 (S53A)
• HP1WW......1,166,400 (OH0XX)
• J28RO............800,382 (F5IRO)
• C4Z.............. 702,150 (5B4AIZ)
• 5C5W.............642,432
• VP2EAT.........508,599 (VE3IKV)
….notice all the 3-pointers!
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Contesting with Verticals & VDAs
2012 – TOP CQ WW DX CW SOSB/10 LP
• C4Z.................600,134 (5B4AIZ)
• UK9AA............481,664
• VK9/OG1M......376,263 (OH1VR)
• HQ2N..............373,524 (JA6WFM)
• PJ7/VA3RA....369,930 (VE3IKV)
• VK6AA............355,840 (VK2IA)
….notice all the 3-pointers!
Year 2: Results using a 10m monoband 0.64 lambda gain vertical:
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Contesting with Verticals & VDAs
Year 3: Results using a 10m monoband 0.64 lambda gain vertical:
2013 – TOP CQ WW DX CW SOSB/10 LP
• NP3A...........1,060,352
• FJ/VA3RA......625,664 (VE3IKV)
• N8II.................434,000
• C6AZZ............430,000 (KQ8Z)
• OK1FDR.........408,519
• WB4TDH.........344,998
……still all with only a keyer & a paper log!
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Contesting with Verticals & VDAs
Vertical Directive Arrays (VDAs)
• Used by recent DXpeditions TX6G, T32C, VP6DX,
FT4TA, etc. rather than low horizontal yagis (10-20m)
• The VDA is a 2-element ½ wave yagi in the vertical
plane, with a wire dipole driven element and a wire
reflector behind it
• Broad 139o beamwidth in the horizontal plane
• Low 7o elevation angle in the vertical plane
• 8dB gain relative to a low horizontal beam reported
when used over sea-water wetted sand, or when used
elevated over normal ground
• 30dB null at the rear (!)
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Contesting with Verticals & VDAs
The 2-el wire VDA
Forward direction
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Contesting with Verticals & VDAs
BAND MAST BOOM LB HB LF D/2 R/2 DS RS d1 d2
20m 12.5m 4m 1.78m 6.24m 6.0m 4.77m 5.07m 0.46m 0.42m 1.62m 1.51m
17m 10m 3m 1.39m 4.87m 4.6m 3.69m 3.97m 0.37m 0.33m 1.30m 1.19m
15m 10m 3m 1.19m 4.45m 4.2m 3.18m 3.40m 0.31m 0.28m 1.09m 1.01m
12m 8m 3m 1.01m 3.91m 3.7m 2.70m 2.88m 0.26m 0.24m 0.91m 0.87m
10m 8m 3m 0.89m 3.66m 3.4m 2.39m 2.55m 0.23m 0.19m 0.81m 0.67m
2-el VDA dimensions for each HF band - 20m to 10m*
* Courtesy G3WGN & G3SVL
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Contesting with Verticals & VDAs
The 2-el wire VDA has approx 30dB F/B ratio!
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Contesting with Verticals & VDAs
2-el wire VDA cardioid pattern in the horizontal plane
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Contesting with Verticals & VDAs
VSWR plot for 12m version of VDA
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Contesting with Verticals & VDAs
• If you don’t have a conductive salt-water ground, elevate the antenna as high as possible in order to get a clear path to the horizon, otherwise you will get reduced performance
• For use at the beach, the following are the min. recommended heights of the boom above ground:
20m – 6.24m; 15m – 4.45m; 10m – 3.66m
• Away from the beach, raise the boom as high as you can
• Boom and support mast must be composite non-conducting material
• Coax feedline should exit the boom at the center, at a 90o angle for at least 1 wavelength before dropping to the ground. Ferrite common-mode chokes may be necessary on the feedline.
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Contesting with Verticals & VDAs
20 meter elevated ground-plane vertical at CY0X - 2008
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Contesting with Verticals & VDAs
Thanks – any questions?