NIST Radio Station WWVH

NIST radio station WWVH broadcasts time and frequency information 24 hours per day, 7 days per week to listeners worldwide. The station is located on the Island of Kauai, Hawaii on a 12 hectare (30 acre) site near Kekaha at Kokole Point. The information broadcast by WWVH includes time announcements, standard time intervals, standard frequencies, UT1 time corrections, a BCD time code, geophysical alerts, marine storm warnings, and Global Positioning System (GPS) status reports.

Broadcast Frequencies

WWVH operates in the high frequency (HF) portion of the radio spectrum and radiates 10,000 W on 5, 10, and 15 MHz, and 5000 W on 2.5 MHz. Each frequency is broadcast from a separate transmitter. Although each frequency carries the same information, multiple frequencies are used because the quality of HF reception depends on many factors such as location, time of year, time of day, the frequency being used, and atmospheric and ionospheric propagation conditions. The variety of frequencies makes it likely that at least one frequency will be usable at all times.

Antennas

The 5, 10, and 15 MHz antennas are phased array vertical dipoles. They consist of two half-wave vertical dipoles that are separated by a quarter-wavelength and driven 90 degrees out of phase. These antennas radiate a cardioid pattern with the maximum gain pointed toward the west. The 2.5 MHz antenna is a half-wave vertical that radiates omnidirectional patterns. Each frequency also has a vertical monopole standby antenna connected to the standby transmitters, in the event that the primary system fails.

Modulation

The signals broadcast by WWVH use double sideband amplitude modu­lation. The modulation level is 50 percent for the steady tones, 50 percent for the BCD time code, 100 percent for the second pulses and the minute and hour markers, and 75 percent for the voice announcements.

Other Information about WWV and WWVH ...

	NIST Time and Frequency Services (NIST Special Publication 432)
	A detailed 80 page overview of NIST time and frequency services and how to use them. Chapter 3 is all about WWV and WWVH.
	Frequently Asked Questions
	Answers to frequently asked questions about the NIST Radio Stations
	Manufacturers of Time and Frequency Receivers
	Links to manufacturers of WWV/WWVH and other time and frequency receivers
	WWV/WWVH 15 MHz Signal Strength versus Time
	As monitored by the High Frequency Active Auroral Research Program (HAARP) in Gakona, Alaska