WWVH Transmitting AntennasWWVH 15 MHz drooping-ground-plane antenna array
WWVH transmits time and frequency standard signals from Kauai, Hawaii on 5, 10 and 15 MHz using separate arrays of two half-wave vertical drooping-ground-plane dipoles spaced a quarter-wave-length apart. The two dipoles in each array are driven 90 degrees out-of-phase with each other to create a cardiod radiation pattern that has maximum gain toward the west and a deep null toward the east to reduce interference to WWV's transmissions on the same frequencies from Fort Collins, Colorado. The Salt Lake City receiving site is situated in the radiation null (minimum signal) direction, which makes WWVH's signals on those three frequencies much weaker here than in any other direction.
Omni-directional Vertical Radiators
2.5 MHz WWVH transmissions are made from an omni-directional vertical radiator, because the potential for significant interference with WWV transmissions on that frequency normally is lower. WWVH also has standby omni-directional vertical radiators connected to standby 2.5, 5, 10, and 15 MHz transmitters that can be used in the event of antenna or transmitter failures.
Number of Radial Wires
Note the large number of drooping radial wires used in the radiators above. Three or four drooping radials are adequate where radiators of this type are high (in terms of wavelength) above ground. However, the closer they are to ground, the larger the number of radials that must be used to avoid high ground losses.
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