Since radio signals can cross multiple time zones and the international date line, some worldwide standard for time and date is needed. This standard is coordinated universal time, abbreviated UTC. This was formerly known as Greenwich mean time (GMT). Other terms used to refer to it include "Zulu time" (after the "Z" often used after UTC times), "universal time," and "world time."
UTC is used by international shortwave broadcasters in their broadcast and program schedules. Ham radio operators, shortwave listeners, the military, and utility radio services are also big users of UTC.
Greenwich mean time was based upon the time at the zero degree meridian that crossed through Greenwich, England. GMT became a world time and date standard because it was used by Britain's Royal Navy and merchant fleet during the nineteenth century. Today, UTC uses precise atomic clocks, shortwave time signals, and satellites to ensure that UTC remains a reliable, accurate standard for scientific and navigational purposes. Despite the improvements in accuracy, however, the same principles used in GMT have been carried over into UTC.
UTC uses a 24-hour system of time notation. "1:00 a.m." in UTC is expressed as 0100, pronounced "zero one hundred." Fifteen minutes after 0100 is expressed as 0115; thirty-eight minutes after 0100 is 0138 (usually pronounced "zero one thirty-eight"). The time one minute after 0159 is 0200. The time one minute after 1259 is 1300 (pronounced "thirteen hundred"). This continues until 2359. One minute later is 0000 ("zero hundred"), and the start of a new UTC day.
To convert UTC to local time, you have to add or subtract hours from it. For persons west of the zero meridian to the international date line (which includes all of North America), hours are subtracted from UTC to convert to local time. Below is a table showing the number of hours to subtract from local time zones in North America in order to convert UTC to local time:
The second table is direct conversion from UTC to U.S.A. timezones.
A major source of confusion when using UTC is that the date also follows UTC. Suppose your local time zone is Central standard, and you want to hear a shortwave program scheduled to be broadcast at 0400 UTC Saturday. You do the math, and find that 0400 UTC is equal to 10:00 p.m. Central standard time. If you tune in at 10:00 p.m. on Saturday, however, you won't hear the program. Since the date is also UTC, you need to listen at 10:00 p.m. Friday to hear the program.
To hear the latest time in UTC, you can tune to stations WWV, in Fort Collins, Colorado and WWVH, Kauai, Hawaii on 2500, 5000, 10000 and 15000 kHz to hear the time announced in UTC each minute. WWV uses a man's voice to give the time, while WWVH uses a female voice. If you live in the central or eastern United States, and those frequencies aren't usable, you can tune to station CHU, in Ottawa, Ontario, Canada on 3330, 7335 and 14670 kHz, to hear the current UTC time. If you're like many radio hobbyists, you will soon add a second clock set to UTC to your collection of radio gear. Click here for information on 24 hour clocks