Coordinated Universal Time (UTC)

Coordinated Universal Time (UTC), also referred to as Greenwich Mean Time (GMT), Universal Time (UT), or 'Zulu' is an international time scale used in Amateur Radio, astronomical aviation publications and applications, weather reporting, the military, NASA, and other organizations and documents.
Most Amateur radio operators refer to it as UTC.
UTC uses 24-hour (military) time notation and is based on the local standard time on the 0? longitude meridian which runs through Greenwich, England, hence, Greenwich Mean Time. Midnight in Greenwich corresponds to 00:00 UTC, noon corresponds to 12:00 UTC, and so on. It is a universal 'reference' time so anyone who uses it has a 'point in time' reference to a specific location.

Therefore, if you are in a different location than the reference location, your local time would be either earlier or later referenced to that UTC location point.
So in a manner of speaking, everyone using UTC, uses the same clock!
The UTC time is the same worldwide and does not vary regarding the time zone or daylight saving time. UTC is a very accurate atomic time standard sustained by atomic clocks located in national standards laboratories.

So in other words, it doesn't matter where you travel to, whether you're in a hotel in San Francisco or in one of the many Washington DC hotels, the UTC time is the same. Or for that matter, anywhere on earth, the UTC time is still the same!

UTC Conversion Table

Now although everyone uses the same clock so to speak, most of us live in different locations of the earth and in different time zones. If we need to know what time, (UTC), it is somewhere else, we need to convert from our time zone to UTC.
The following table provides for converting between UTC and U.S. and Canadian time zones or in reverse.
UTC is in the far right hand section of table below in red.
Notice that it starts at 00:00 (midnight). The blue numbers below it indicate 'AM', with a break at 12:00 (noon), then the colors change tored 'PM' all the way to 23:00 pm, then it changes back to the top of the column to 00:00, (midnight) all over again indicating one complete 24 hour period. The colors on the table have nothing to do with 'telling time' except to distinguish between AM and PM to help you use the table easier.
The other sections labeled PST, PDT, MST, MDT, CST, CDT, EST, EDT, represent YOUR LOCAL TIME ZONE. If you live in the Centeral Time zone, then you use the section marked CST, if Daylight Savings Time is in effect, you use CDT.
The same goes for the other time zones.
To use the conversion table, here is an example:
Refer to the table below,
Imagine your time zone was CST and your local time is 7:00PM....find the CST section, read down that section until you find 7:00PM then read to the right under the UTC section and read 01:00...so the UTC time that corresponds with 7:00PM CST is 01:00...it's 1:00 AM in Greenwich, England THE NEXT DAY! Now looking at this from the Greenwich time zone at 00:00 to the left, then it would be 7:00 pm in the Central Time Zone THE PREVIOUS DAY. Remember, at midnight, the day changes either forward or backward depending on the direction of your conversion and your location.

Another example:
It is 06:00 UTC...What time is it in the Eastern Standard Time zone?
Reading to the left from 0:600 UTC until you find the EST zone = 1:00AM. If you were looking at the PST section, it would be 10:00pm, the previous day.

Don't forget that the day advances at midnight or retreats to previous day depending on where you are and the dirction of the conversion! You can actually be talking to someone on the radio who is in your future or in your past, depending on your point of view and your reference in time! Time travel without a time machine!........just rf and some distance!
Chart shows Standard and Daylight Savings Time for each zone.
'S' = Standard and 'D' = Daylight Saving time (CST,CDT)

How do you know what the correct UTC time is?
Listing to Time Signals on HF

Several radio stations worldwide transmit precise time signals on HF bands and other frequencies. NIST (U.S.A.), continuously broadcasts time signals with voice announcements over hf radio frequencies from stations WWV in Fort Collins, Colorado and WWVH in Kauai, Hawaii. Both stations transmit on 2.500, 5.000, 10.000, and 15.000 MHz. WWV also operates on 20.000 MHz.
If your HF transceiver has general coverage, you are in luck...Just tune in one of the frequencies and get the exact time. They transmit on AM and you can use either the AM mode on your receiver or zero beat the frequencies with either the USB or LSB mode to hear the voice modulation.
Audio Sample of over the air signal from WWV.
(Note that this is not the actual time, it is an audio recording of about 1 minute and 25 seconds taken from 10.000Mhz during the daytime (CST), using a Yaesu FT-107 receiver in USB mode. You will hear the 'time ticks' and the time announced twice if you play it all the way to the finish.

If propagation is 'right', you can use Canada's Institute for National Measurement station, CHU. It transmits time signals and voice announcements from Ottawa, Ontario. CHU broadcasts continuously on 3.330, 7.335, and 14.670 MHz, also AM as with WWV and WWVH.
So you see, you have several HF frequencies from which to choose to get the 'correct' UTC time using your general coverage receiver.

There are also many other stations around the world that transmits time signals and some are strong enough to be heard in the U.S and Canada. There are many ore on the lower frequencies below standard AM broadcast, but they are extremly difficult to hear due to distances, static and power levels. They are not listed here.

See chart below:

The frequencies are believe to be accurate and remember...propagation plays a big part in receiving them. You also have to remember that radio travel a near the speed of light around the world so there is a split second error for listeners in the U.S. tuned to WWV OR WWVH. Believe me, it is accurate enough to set that old clock on your wall very accurately!

The following is a table of some major time stations reported to be in operation from various sources including radio verification at the time of this article, 2007.
Most ham radio operators will find that the stateside frequencies will be the best to copy with the exception of CHU, Canada using a good general purpose antenna. Those highlighted ingreen are usually very good copy with one or more heard at different times of the day. Note that CHU changed frequency from 7.335Mhz to 7.850Mhz effective 01 January, 2009.