Of all the rabbit holes we technical types tend to fall down, perhaps the one with the most twists and turns is: time. Some of this is due to the curiously mysterious nature of time itself, but more has to do with the various ways we’ve decided to slice and dice time to suit our needs. Most of those methods are (wisely) based upon the rhythms of nature, but maddeningly, the divisions we decided upon when the most precise instrument we had was our eyes are just a little bit off. And for a true time junkie, “a little bit off” can be a big, big problem.
Luckily, even the most dedicated timekeepers — those of us who feel physically ill when the clock on the stove and the clock on the microwave don’t match — have a place to go that’s a haven of temporal correctness: radio station WWV. Along with sister stations WWVB and WWVH, these stations are the voice of the US National Institutes for Standards and Technology’s Time and Frequency Division, broadcasting the official time for the country over shortwave radio.
Some might say the programming coming from these stations is a bit on the dry side, and it’s true that you can only listen to the seconds slip by for so long before realizing that there are probably better things to do with your day. But the WWV signals pack a surprising amount of information into their signals, some of it only tangentially related to our reckoning of time. This makes these stations and the services they provide essential infrastructure for our technological society, which in turn makes it worth your time to look into just how they do it.
First On The Air
Callsign WWV has been around and active longer than US commercial radio itself. WWV was assigned as an experimental license to the National Bureau of Standards, the predecessor of the NIST, back in 1919. By September of 1920, WWV was broadcasting weekly concerts on 600 kHz, beating Pittsburgh station KDKA to the airwaves by a couple of weeks.
In those early days, WWV was very much a solution looking for a problem, alternating between music and farm market reports, and focusing on the Washington, DC area, where the NBS offices were located. In 1922, someone must have noticed that the “S” in NBS stood for “standards,” and WWV’s signal became a reference frequency standard for other broadcasters in the burgeoning industry. A succession of technological advances gradually increased the accuracy of WWV’s signals from a few tenths of a percent to the parts-per-million level, which was vital for allocating spectrum in the gold-rush years of the 20s and 30s.
WWV’s signature time programming didn’t start until nearly the end of WWII. Shortly thereafter, In 1948, station WWVH went on the air from the Hawaii Territory, in a nod to the country’s growing interest in events in the Pacific Basin. It wasn’t until 1950 that Morse time announcements gave way to the now-familiar voice time announcements; by the late 50s, frequency control on the station’s 5 MHz, 10 MHz, and 15 MHz frequencies was better than 200 parts per billion.
In 1966, the station moved to its current location in Fort Collins, Colorado, only about 80 km away from the NIST laboratories in Boulder, Colorado that house the US standards for time and frequency. The relocation put WWV on the same site as WWVB, a low-frequency (60 kHz) station that transmits nothing but encoded time signals at a scorching 70,000 watts effective radiated power (ERP). WWVB is designed to reach the entire United States for at least part of every day, and if you’ve got a “radio-controlled” clock or watch, chances are it’s listening to WWVB.
Atomically Accurate
The heart of WWV and WWVB operation in Fort Collins centers around the “Screen Room,” a Faraday cage-shielded room housing the station’s cesium frequency standards and time code generators. The three redundant oscillators derive their time and frequency information from the NIST Time Scale, called “UTC(NIST),” maintained at the Boulder NIST lab using a suite of hydrogen maser and cesium oscillators, which in turn are calibrated against a cesium fountain oscillator. The station oscillators are compared to UTC(NIST) every day and corrected as needed. Only one oscillator serves as the station master at a time; a supervisory system monitors the output of each oscillator and automatically promotes one of the backups to master status if anything goes wrong with the time signal.
The station master cesium oscillator is the heartbeat of the entire system. Its 5 MHz signal — actually, at 1 part in 1014, that’s 5.00000000000000 MHz — gets divided down to multiple reference frequency signals that control both time code generators and transmitter carrier frequencies. WWV currently broadcasts on 2.5 MHz, 5.0 MHz, 10.0 MHz, 15.0 MHz, and 20.0 MHz, with an experimental signal at 25.0 MHz; WWVB still operates at 60 kHz.
Audio time signals and voice announcements are generated by the time code generators in the Screen Room. WWV uses a male voice for time announcements while WWVH, which transmits on some of the same frequencies, uses a female voice to avoid confusion. The announcements are concatenated from digitally recorded phrases spoken by professional announcers; WWV currently uses the golden voice of Atlanta’s John Doyle.
Sounds Around The Clock
While the voice announcements on WWV are certainly its biggest draw, there’s so much more going on in these signals. The audio signals are carefully engineered to relay the maximum amount of information in the most flexible way possible, giving users access to all sorts of valuable information. The most obvious component of the audio signal is the constant tick of seconds. Each tick is really a 1,000 Hz sine wave that lasts for five milliseconds — a mere five cycles — which sounds like a tick. The seconds signal sounds every second of each minute, except for the 29th and 59th seconds, and for whenever a leap second is called for. At the top of each minute, the seconds pulse is changed to a 1,5000 Hz tone and extended to 800 ms. For the first sixteen seconds of every minute, you might hear double clicks for certain seconds, which serve as correction indicators between Coordinated Universal Time (UTC) and UT1, a time standard based on the rotation of the Earth. The number of doubled clicks tell you how many tenths of a second UTC and UT1 differ by; if the clicks are doubled from seconds 1 through 8, that means UT1 is ahead of UTC, whiles seconds 9 through 16 indicate that UT1 is lagging.
In addition to the ticks, the audio signal contains an audio tone that changes depending on the minute of the hour. Tones alternate between 500 Hz for the even-numbered minutes and 600 Hz for odd, with a 440 Hz “A440” tone used for the second minute of each hour. Certain other minutes are blocked out as reserved as well, but generally contain the tone normally designated for that minute. The audio tones, which can be used to calibrate audio equipment, are suppressed for one minute during the station identification announcements at the top of the hour and 30 minutes, and are suppressed entirely from 43 to 51 minutes and again for minute 59. The idea behind these blocks of silence is to prevent interference with WWVH’s signal, while the switch to A440 once each hour is meant to be used as a signal by systems that can receive WWV signals but don’t have the equipment to decode the subaudible time signals discussed below.
WWV also devotes several minutes of each hour to special announcements by official government agencies. Each announcement gets a 45-second block. Storm warnings from the National Weather Service are broadcast during minutes 8-11 when needed, with updates on GPS constellation status and geophysical alerts going out on minutes 14, 15, and 18. There’s also an interesting project called the WWV/WWVH Scientific Modulation Working Group, which aims to broadcast special signals once per hour (8 past the hour for WWV, 48 past for WWVH) to study the ionosphere and propagation. The signal is a series of chirps, tone sweeps, and broadband noise developed with the help of Ham Radio Citizen Science Investigation. Watch out — the audio is quite loud.
Automatic Time
In addition to the audible content, WWV sends out a separate coded time signal. The signal is continuously transmitted as a 100 Hz tone that uses binary-coded decimal (BCD) format. Each bit is squeezed into the space after the seconds tick finishes and consists of the 100 Hz tone at two different amplitudes. The length of time the tone stays at the high amplitude indicates whether the bit is a binary one or zero, or a “marker” bit. A full frame of time code data takes 59 seconds to send, with each frame containing fields for hours. minutes, and seconds, plus the day of the year, last two digits of the current year, flags for Day Saving Time and leap years, and the UT1 correction factor and sign. WWVB, whose only business is sending these time signals, has a slightly different frame arrangement, but uses the same encoding scheme.
All things considered, the amount of information jammed into WWV’s audio signal is pretty amazing. It’s also kind of fun to realize that WWV’s signal can consumed on so many different levels, from the casual listener just wanting to know the time to control of automatic systems and calibration of systems ranging from audio frequencies all the way into the lower reaches of the VHF band.
How can a relatively tiny watch or even a clock, pick up a 60KHz RF (?) signal, with wavelength of 5km, a
couple thousand kilometers away? I know they work and it’s a strong signal, but that’s still amazing.
https://www.citizenwatch-global.com/technologies/radiocontrolled/index.html
They do some quite small antennas. I didn’t realise they go quite this small until I went looking because of your question.
Look up Loopstick antenna. It is a coil around a ferrite core. What’s also amazing is that the RX and clock all works on one AA battery for a year or more.
I have a Citizen ECO drive (solar) watch that is over 30 years old and still ticking! It doesn’t have an atomic clock in it though. I also have an ECO drive with atomic clock that is over 5 years old and still ticking. It’s great to never have to set it. Citizen is my favorite watch brand.
You do realize right, that the so called “atomic clock” in the watch isn’t really in the watch, but is in NIST HQ, and controls the watch timing through a VLF radio link? I’m actually just mentioning it for the benefit of others who may not know. But it is still an amazing work of the technical art.
All the time, all the time – WWV – The Tick: https://www.youtube.com/watch?v=9CpsPgXyIm8
Somewhere I have a recording of this; goid to know it’s still on line. I will down load it to my current disaster of a phone. Thanks
I bought a small short wave radio to receive time ticks for calibrating some stuff. You need to get one with single side band (SSB) or it won’t work.
There is also a phone number you can call and get same time ticks. Of course subject to the lags and latency of your phone system but it can potentially be close enough. (303) 499-7111
For a good time call (303) 499-7111. Its been saved in my phonebook for 15 years or more.
This one has a WWV band selection, for example.
https://www.rigpix.com/yaesu/ft101.htm
It’s on 10 MHz, a very clean frequency that’s ideal for easy adjustment of the radio (good to read).
The astronomy people rely on WWV, too, by the way.
https://swling.com/blog/2018/08/astronomers-organizing-to-save-wwv/
It’s an AM signal. Not sure why you would need SSB unless you wanted to hear the carrier itself (to check the accuracy of your radio’s LO).
Why won’t an AM radio work? i guess it depends on what you are trying to accomplish. For the 3 oscillator method you can use an SSB radio, an old- style AM/CW receiver, a Regen radio, or an AM receiver plus a separate signal generator near, but not on, the frequency to be measured. I usually use my station receiver, but i also for field use have an STR-1 Standard Time Receiver to which I have added a BFO and an S meter. It’s a little gold colored box that I can hold in one hand and will receive WWV anywhere in the 48 mainland states on a 3 ft whip, and often will pickup WWVH. It lets me calibrate in the field without lugging around a full size station transceiver.
Certain GPS receivers will output accurate 1pps time ticks also, and are not subject to the vagaries of atmospheric doppler effects. But not all GPS receivers put out an accurately timed 1pps signal, only ones that sre properly controlled by the sats. For more info, see the Time Nuts website, “timenuts.com” IIRC. Also visit QRP Labs site for GPS kits and Pll Kits that will let you build clocks and standards.
I lived about a mile from WWV when I was growing up. Most of the noise in my electronics projects was from that station.
I could know the exact time with a headphone, a diode, and about two feet of wire for an antenna.
“I could know the exact time with a headphone, a diode, and about two feet of wire for an antenna.”
That surely was fun, I loved to build crystal radios, too. 🙂👍
However, there’s much more to get out of a crystal radio if it’s a tuned circuit! 😃
An AM coil made of insulted copper wire (wound on a toilet paper roll) and a metal knob on it (-for selecting the tapping point; it’s being held by a metal bar-) can greatly incrase performance.
The wire surface facing torwards the metal knob must be blank, of course.
Such crystal radios were sold as kits in the 1970s to 1990s, too.
Using a variable capacitor, if available, is even better.
A battery can help to overcome the minimum voltage needed for the glass diode to work, also. An 1,5v battery is enough, since the diode needs 0,3 to 0,7v. The tricky part is to avoid burning the diode. There are schematics which provide tips. A resistor helps reducing current, I vaguely remember.
The battery can be built DIY style, too, so the being independent part is still being provided. A glass of lemon juice and a pencil and a metal coin may do. The voltage is important, rather than the current.
If you like, please have a look at places like “Jogi’s Röhrenbude” (Jogi’s tube shack) or “Welt der alten Radios” (world of old radios). They have schematics for interesting radio projects of all sorts.
Especially the spider web coils are interesting to make.
They have a high Q factor and are excellent for crystal radios. ^^
https://www.jogis-roehrenbude.de/
https://www.welt-der-alten-radios.de/
I thought I’d discovered free power when I replaced the tiny earpiece in my crystal radio set with a grain of wheat bulb and could see the audio. I mean, for some super low power requirement projects, it’s probably a valid option.
In the early 60s, my Dad and built a ‘dual stage’ crystal radio. The first stage received the target station, the second stage was tuned to the strongest station in the area, which was then rectified to power a 1 transistor amplifier which amplified the output of the first stage. I was able to drive a small speaker with it.
That reminds me of an old transceiver circuit where the transmitter was powered by the voice, using a dynamic microphone and rectifying the the signal to provide power for the oscillator. Only a few milliwatts of transmitted power, but still a good demonstration of ingenuity.
Kool; I’ve seen that project around that time in a magazine, Popular Electronics I believe. That idea has always stuck in the back of my head.
A way to increase the power output of the microphone powered transmitter would be to use a crystal mike, which can produce up to 500 mv, as opposed to a few mv from a dynamic mike.
Crystal radios…a great segue! Time to reminisce!
The World Book encyclopedia*** had instructions for building one, the tuner being a toilet paper core wound with enameled wire. The dime-store-type mail-order houses (Hanover House?) sold a little 2″ square unit that actually looked like a tiny radio. Fake speaker grill on the front (it used an earphone); tuner looked like a short antenna, push it out or in to tune; alligator clip to attach to a ground. That was how I learned that the metal finger-stop on a rotary phone was grounded.
Then there was junior high shop class where we got to build one from commercial components; small coil-wound tuner and 1N34 diode. Objective was mostly soldering ability. (Anecdote time: One poor sap understood neither the concept nor the practice of soldering. He failed repeatedly at an assignment that simply required soldering a pigtail, a side tap, and a straight connection using 14 ga wire; a xtal radio was an absolute impossibility for this klutz.)
*** “World Book”; “junior high”; “Hanover House”; “dime store”; “rotary phone”……ok, I think I’ve dated myself sufficiently… :-)
Don’t forget “shop class, ya (fellow) withered old coot; do they even have shop anymore? Our Voc Ed building has been empty for 20 years. And yes, I remember those mail order crystal sets, specifically one that looked like a rocket with the tuning knob for the nose cone.
So how do you “insult” copper wire? What sort of names do you call it, and of what nefarious deeds and failures do you accuse it? Just kidding, I know, auto foul-up has struck again.
Call it CCA, it hates that!
On behalf of copper, thanks, I’ve never been so insulated in my life
Cool that you didn’t need a tunes circuit to pick it up!
I tried to build a crystal radio tuned to pick up WWV at 10MHz a few years back; it unfortunately ended up swamped by a couple of local AM stations here in the Pacific Northwest. That is, unless I attached one of those little Radio Shack audio amplifiers to the output, at which point it would get swamped by a local _FM_ station; I’m still a little confused about the mechanism there.
(About the same time, I got an old DX-160 radio working and picking up WWV at 5, 10, and 15MHz, so at least something could pick it up.)
Back when crystal set radios were mainstram, a lot of development was done on the tuning circuits, with improvements such as loose couplers, double-tuned circuits, and “wavetraps”, which would short out
interfering signals. A little poking around online will hook you into some interesting stuff, as there are people who are fascinated by early technology such as crystal and regenerative radios.
You can also call them to listen in to the WWV broadcast “live”. Obviously there will be more latency from the phone system than speed of light delay through radio, but you can hear what it sounds like. 303-499-7111
I crewed on a yacht from the West Indies to the UK centuries ago. The skipper used WWV on my SW radio to check his chronometer IIRC. Something so very cool about being able to get the exact time like that. I was never late for an appointment after that!
When I worked SW as a kid I got QSL cards from stations around the world and I still have my cards from WWV and WWVH. Yeah no big deal but each card was and is special to me. Listening to radio from around world kept the nights on the farm interesting.
I recall a couple of global nautical charts from decades ago that had some funny curved lines (dashed?) marked with ‘WWV’ followed by what I can only suppose was a time lag (for that region due to distance from WWV tx site) numerical value. Anyone ever seen this or have further info on who/how it was used?
Back in the 1980s the New York Stock Exchange had a WWV receiver in it’s Communications Control Center which supplied time to all the clocks and computers. This was necessary to ensure that all transactions complied with regulations–both government and internal.
I too made good use of WWV and even stopped by for a visit in 1975. They were happy to accommodate visitors and showed me their HP rack mount atomic clocks inside their faraday shielded room. The transmitters were all Colins and they used a Colin’s KWM2 ham transceiver to communicate with their Hawaii station. It was a very nice tour and very friendly people.
But what’s not mentioned in this article is the Canadian time standard CHU Canada. They operated on 7.335 MHz until 2009 and thus could be received on a typical ham receiver tuned to the 40m ham band. The wwv stations are not anywhere near ham bands so their signal wasn’t available on many ham rigs like chu was.
Chu is still transmitting around 7.8 MHz and has a website that describes their format. One interesting feature of their format is the ascii encoding of the time. Here’s what their website says “The warble tone at seconds 31 to 39 allow any computer with a Bell 103 compatible 300 bps modem to receive and decode an accurate source of time. The details on the CHU broadcast codes can be found here.” With the changing landscape of shortwave radio it’s nice to have some dependable stations to use for demonstrations.
Some of the WWV frequencies I see are very close to the edge of at least one ham band and probably within the range of many common shortwave radio receivers. E.G. 12m and 25MHz.
The majority of ham transceivers made in the last 40 years feature high quality general coverage receivers, so stations like CHU may be easily received.
I’m wearing my reliable 20-year-old Casio Waveceptor watch that picks up a time signal from Rugby ( on 600KHz I believe ) here in the UK. Super reliable and has never let me down except for the one time I arrived very late to a hotel one spring at the start of a stressful business trip.
I arrived at 2:00 am in the morning and had to be up at 7:00. I was just checking my watch and thinking I would be able to just about squeeze in 4 1/2 hours sleep when, as I was looking at it, the watch skipped forward a full hour. It was auto-correcting for British Summer Time. That was a shorter night followed by a long days work. :-(
“Casio Waveceptor”
Use mine everyday. LOVE IT!!
Unlike my Timex, it does not lose 15 sec. a day :)
(Well…..it may, but WWVB fixes that!! haha)
I had a Timex (actually it is in my underwear drawer; because the wrist band mounts are broken) that would lose maybe 15 seconds between DST changes.
Here’s a fun science experiment. Feed the WWV audio signal into an oscilloscope. Hook the PPS output of a GPS to the trigger input. You will see the five ticks plotted on the scope, but it won’t start right at zero. You are measuring the speed of light propagation.
For me, this is 8 ms. But one night it was 30 ms. I was confused until I heard a woman’s voice and realized I was getting WWVH instead WWV!
And before someone corrects me, this is best done with an analog radio that has minimum internal latency. I used a TS 530 :)
Actually, the speed of light is fairly constant; I think the offset on the scope trace is the distance the radio wave has travelled, which is why WWVH showed a greater offset, being much farther away.
I’ve heard the ticks and then tick-icks fading in and out then the woman’s voice is heard in the background then the top tone mark and a man’s voice in the foreground following. The tick-icks are light speed delay of Hawaii farther than Colorado to Indiana. Fun to just hear the delay knowing what it is.
I am loving this post. In the 70’s I would sync my Timex to WWV. The next day in grade school, me and a friend (who had sync his watch at home too) would love to watch both our watches second hand clicking in sync. At that point time they only announced the time every 5 minutes so the was a little bit of a pain. For some parts and fun WWV projects Check out https://universal-solder.ca/product-category/atomic-clock-radio-receiver/
I first heard WWV while riding in a car with a couple hams (circa 1975).
I commented that it had to be the boringest job in the world 🌎, to be announcing the time like that.
B^)
In the early 1970s, I was a ham operator, working from our Iowa farm. I frequently pulled up WWV to sync my watch to The One True Time. Then in college, in my electronics class, I designed and built a clock circuit that set itself from WWVB.
After college I moved to Fort Collins, Colorado, and I can see the WWV towers from my living room window. :-)