Zulu Time = GMT (Greenwich Mean Time) = UTC (Universal Coordinated Time)
Most Hams speak of this Time as UTC time but
all three are basically the same.
In 1928 The Name GMT was adopted internationally as the Universal time
so what exactly was / is GMT time?
Well, GMT = Greenwich Mean time is the
Local time at the Zero Meridian on Earth
And That Zero Meridian passes through Greenwich England
Originally it was only referred to as GMT but after Atomic Clocks were invented and came into widespread use in 1972, the terms UTC and Zulu Time became popular
because
Use of The Atomic Clock enabled leap seconds to be added to make time more accurate --
So GMT became known also as UTC or Zulu Time
But this time was and is still the local time at the Zero Meridian on Earth which still passes through Greenwich England.
So the only thing that changed was its name --
so now it is known as GMT UTC and Zulu Time
Therefore
UTC Zulu and GMT (whichever name you want to use) is
an international time standard
now calculated by an atomic clock
and incorporating occasional leap seconds to compensate for changes in the rotation of the earth.
It serves as the basis for standard time around the world
and uses the 24 hour clock.
Thus the local time in Greenwich England is considered to be the same time all around the world -- and it does not vary regarding Daylight Savings time or Time Zones.
The UTC (aka GMT and Zulu time) is also the basis for Broadcast time signals so everyone can be on the same page and know when to tune in to Short Wave Broadcasts or to participate in events and more.
if it is midnight in Greenwich England it is 00:00
if it is noon in Greenwich England it is 12:00
if it is 8 pm in Greenwich England it is 20:00
Of course if you do not live on the Zero Meridian in Greenwich, England, you will have to make adjustments so you will know what your local time is if you want to correlate it with the UTC (GMT Zulu) time.
You may live in an area with Daylight savings time and a different time zone from Greenwich England.
So
If you want to listen to a ShortWave broadcast you will have to convert your time to UTC time
Or if you want to participate in a contest such as Field Day or any of the many contests which list and record their times in UTC time -- you will have to make that conversion so you will know when to start and stop and what time in UTC you made your contacts.
Also if you want to exchange contact times with someone with whom you chatted on the radio, you use UTC times.
How do you make this conversion? Well, I’ll explain in a few minutes. Hang on.
But First
you will want to know how to determine the precise UTC time
And fortunately this precise UTC time is available from Broadcast Signals which you can hear on a standard Short Wave Receiver in the AM Mode
and
on your HF Rig in either USB or LSB mode
They are broadcast from several locations around the world.
In the US they are broadcast from WWV (Whiskey Whiskey Victor) which is the National Institute of Standards and Technology station -- located near Ft. Collins Colorado.
WWV uses a Male voice to announce the times
And There is a sister station WWVH (Whisky Whisky Victor Hotel) located in Hawaii that broadcasts in Morse Code every 5 minutes.
Both stations broadcast on 2.500 5.000 10.000 and 15.000 MHz
and WWV also broadcasts on 20.000
Other Nations such as Canada have a similar broadcast and if propagation is right you can hear Canada’s announcements from Ottawa Ontario on
3.330 7.335 and 14.670 MHZ
There are also broadcasts from other countries and locations on lower frequencies but they are very hard to hear due to distances, static, and power levels.
Now, as I mentioned earlier -- you will want to change UTC (aka GMT or Zulu) to your local time and be able to adjust accordingly if you are in Daylight Savings time, etc.
The way to do that is to consult a chart.
There are many charts out there on the internet to help you. You might want to print one out and keep it close to your radio.
Here is a link to a website with additional information about Zulu time and it also has charts to use to make the conversions from GMT UTC Zulu time to your specific location. HERE'S THE LINK
That webpage also has a recording of what the Time announcements sound like if you don’t yet have a SW receiver or HF radio. So scroll down till your find it -- or click here