Tucked among the broadcasters and hams on the radio spectrum is a small family of stations that broadcast something stranger than music or news: they broadcast time itself, and a perfectly steady frequency to go with it. Their product isn't a program — it's precision. For a century these stations have given mariners a chronometer check, engineers a calibration reference, and, more recently, the wall clock in your kitchen the means to set itself twice a year without a stepladder. This page lists the standard-frequency and time-signal stations of the world, past and present, with the American trio — WWV, WWVH, and WWVB — at its center. It's a companion to the U.S. shortwave broadcasters page.
Noncommercial hobby compilation, gathered from public sources including NIST. Corrections welcome — chris@n6jet.com.
What a time station actually does
Is it AM? How the time stations modulate
The American stations — WWV, WWVH, WWVB
WWV: the oldest voice on the air
A time-and-frequency station is built around an atomic clock, and everything it sends is locked to that clock. The carrier wave itself is a standard frequency — tune a 10 MHz receiver to WWV and you have a 10 MHz reference good to a fraction of a part per billion, accurate enough to calibrate a lab oscillator. Onto that carrier the station layers the time: a tick every second, a tone at the minute, a spoken announcement of the hour, and a digital time code that a small chip can decode to set a clock automatically.
There are two broad families. The shortwave (HF) stations — WWV, WWVH, CHU, BPM, RWM — can be heard across oceans, and for generations they were how a ship checked its chronometer or a ham calibrated a rig. The longwave (LF) stations — WWVB at 60 kHz, DCF77 at 77.5 kHz, MSF, JJY — don't travel as far but punch through walls, which is exactly what a self-setting “atomic” alarm clock on a nightstand needs. The earliest of all were a U.S. Navy experiment: the Naval Observatory was already sending wireless time signals as a navigation aid by about 1904, two decades before broadcasting as we know it began.
Mostly AM — but with a clear split between the two families, and a reminder that the steady carrier itself was always the real product.
The shortwave stations are AM you can simply listen to. WWV and WWVH use ordinary double-sideband, full-carrier amplitude modulation, exactly like an AM broadcast station — which is why you can tune 5 or 10 MHz in AM mode and just hear them. On WWV every second brings a tick that is literally five cycles of a 1000 Hz tone, about 5 ms long; WWVH sends its tick at 1200 Hz so the two can be told apart on their shared frequencies. A longer 800 ms tone marks the top of each minute, a 1500 Hz pulse marks the hour, and steady 500 Hz and 600 Hz reference tones alternate through the hour, with a man's voice (WWV) or a woman's (WWVH) reading UTC. The ticks and markers run at full modulation while the tones and voice sit lower, so the on-time tick always punches through. The digital time code rides underneath all of it as a low-level 100 Hz subcarrier — an extra tone you barely notice, but a clock chip reads it one bit per second.
The longwave clock-setters are amplitude-keyed, with no voice at all. WWVB on 60 kHz carries no program; it sends one bit per second by dropping its carrier power 17 dB at the start of each second and restoring it 0.2, 0.5, or 0.8 second later to mean a zero, a one, or a position marker. That is amplitude modulation in the on/off sense, but fed to a speaker it would be clicks and hum, not something to listen to — only a receiver chip decodes it. Since 2012 WWVB has layered a second, phase-modulated code on top for tougher reception. Germany's DCF77 works the same way and adds a phase-shift-keyed code that gives its signal a distinctive “noisy” hiss.
And a few are just Morse. Russia's RWM and its relatives send interrupted-carrier markers and Morse identification — straight on/off keying, no AM envelope at all. In every case, the point to remember is that the rock-steady carrier frequency is the standard; the AM, the keying, or the Morse is only the wrapper that carries the time.
All three are operated by the National Institute of Standards and Technology (NIST), with their clocks and frequencies maintained by the Time and Frequency Division in Boulder, Colorado. WWV and WWVH share the same shortwave frequencies and are told apart by voice — a man on WWV, a woman on WWVH.
| Call | Location | Band & frequencies | Notes |
|---|---|---|---|
| WWV | Fort Collins, CO | HF — 2.5, 5, 10, 15, 20 MHz | The flagship, on the air since 1920 — the world's longest continuously operating radio station. Male voice; seconds ticks, minute tones, spoken UTC, a digital time code, and hourly geophysical and GPS-status announcements. |
| WWVH | Kekaha, Kauai, HI | HF — 2.5, 5, 10, 15 MHz | The Pacific sister station, on the air since 1948. Female voice, so listeners who hear both can tell them apart on the shared frequencies. |
| WWVB | Fort Collins, CO | LF — 60 kHz | No voice at all — just a 60 kHz carrier and a time code. This is the signal that sets tens of millions of radio-controlled “atomic” clocks across North America. On the air since 1963; now 70 kW ERP. |
WWV began transmitting in 1920 and has been running ever since, which makes it the world's longest continuously operating radio station — older than the entertainment broadcasters whose band it sits above. It started in Washington, D.C., moved to a series of suburban Maryland sites in 1931, and settled at its present home near Fort Collins, Colorado, in 1966. By 1923 it was already sending standard-frequency signals to the public so that the booming new radio industry could calibrate its gear; since 1945 it has carried official U.S. time, maintained jointly by NIST and the U.S. Naval Observatory.
A few favorite footnotes: in 1958 WWV's 20 MHz signal was used to track the dying Sputnik 1 by meteor-scatter, after the satellite's own electronics failed. Since 2021 WWV and WWVH have carried a deliberately odd burst of tones, chirps, and noise once an hour — a joint experiment with the ham-radio HamSCI project to study the ionosphere. And you can still simply phone the time: WWV answers at (303) 499-7111.
WWV once carried a sixth shortwave frequency, too. 25 MHz was a regular part of its lineup until NIST dropped both the 20 and 25 MHz outlets in 1977; 20 MHz returned the next year, but 25 stayed dark for 37 years. Then in 2014 a listener's emailed request prompted WWV's lead engineer to switch it back on — “for old times' sake,” on an experimental basis — and it has lived on intermittently ever since at low power, useful mainly as a propagation beacon for the 10- and 12-meter bands. It was never restored to the official continuous lineup, which is why the table above lists 2.5 through 20 MHz and stops there.
It came close to ending. NIST's 2019 federal budget request proposed defunding and shutting down all three stations; hams, mariners, and clock-watchers objected loudly, Congress preserved the money, and WWV, WWVH, and WWVB stayed on the air — where they remain today.
A selection of the standard-frequency and time-signal stations still operating outside the United States. As in America, the shortwave stations reach far while the longwave ones quietly set Europe's and Asia's radio clocks.
| Call | Location | Band & frequency | Operator / notes |
|---|---|---|---|
| DCF77 | Mainflingen, Germany | LF — 77.5 kHz | Run by Germany's national physics lab (PTB) since 1959; sets most of Central Europe's radio clocks, and now also carries civil-protection alerts and weather data. |
| MSF | Anthorn, England | LF — 60 kHz | “Time from NPL,” the British time code; moved here in 2007 from its historic home at Rugby. |
| JJY | Fukushima & Kyushu, Japan | LF — 40 & 60 kHz | Two NICT longwave stations between them cover all of Japan, conveniently on the same 40/60 kHz pair used by clock chips elsewhere. |
| BPM | Pucheng, China | HF — 2.5, 5, 10, 15 MHz | China's National Time Service Center shortwave signal (with longwave sister BPC on 68.5 kHz). |
| RWM | Moscow, Russia | HF — 4996, 9996, 14996 kHz | A continuous Morse-and-markers standard-frequency signal; Russia also runs longwave RBU and other regional outlets. |
| ALS162 | Allouis, France | LF — 162 kHz | France's time code rides the old France Inter longwave transmitter; the radio programming ended in 2016, but the time-and-frequency signal kept running. |
Others still on the air at various times include YVTO (Caracas, Venezuela, 5 MHz), HLA (Daejeon, South Korea), ATA (New Delhi, India), LOL (Buenos Aires, Argentina), and BSF (Taiwan).
Japan's time station deserves more than a single line, because for most of its life JJY was a shortwave broadcaster every bit as familiar across the Pacific as WWV. It went on the air on January 30, 1940, which made it the world's second national standard-frequency station, behind only WWV. It began on shortwave, radiating frequency references on 4, 7, 9, and 13 MHz; spoken and Morse time signals were added in 1948, and after a wartime pause the station was back in public service by 1946.
By the late 1950s JJY had settled onto the same international standard set that WWV used — 2.5, 5, 8, 10, and 15 MHz — with Morse and a Japanese woman's voice announcing the time before every tenth minute (“JJY JJY 1630 JST”). That 8 MHz channel was something of a JJY signature; most of the world's time stations skipped it. The 2.5 and 15 MHz outlets closed in 1996, leaving 5, 8, and 10 MHz at the end.
Then, like Japan's clocks, JJY moved down in frequency. An experimental longwave transmitter, JG2AS, had been running at 40 kHz since 1966, and in 1997 the lab judged that longwave was steadier, less interference-prone, and far more useful for the radio-controlled clocks then spreading nationwide. The first official LF station opened on Mount Otakadoya (40 kHz) in June 1999; the shortwave service signed off for good on March 31, 2001; and a second LF transmitter on Mount Hagane (60 kHz) came on that October. Those two longwave stations — listed in the table above — are the JJY that sets Japan's clocks today.
Time and frequency stations — and a couple of navigation systems used for timing — that have left the air. Several were retired as satellite navigation (GPS) made a steady terrestrial reference seem less essential, though jamming and indoor reception keep the old stations relevant. The newest loss is Canada's CHU, switched off on June 22, 2026.
| Call / system | Location | Band | Story & fate |
|---|---|---|---|
| CHU | Ottawa, Canada | HF — 3330, 7850, 14670 kHz | Canada's official time signal for more than a century, and the shortwave neighbor North Americans knew best after WWV — bilingual English/French voice on a reduced-carrier single-sideband signal. The National Research Council switched off the transmitters on June 22, 2026 as a budget measure; official Canadian time now goes out only by telephone, web clock, and network time protocol. |
| WWVL | Fort Collins, CO | VLF — 20 kHz | NIST's experimental very-low-frequency station, 1963–1972. Its antenna didn't go to waste — it was later rebuilt into part of WWVB's array. |
| MSF (Rugby) | Rugby, England | LF — 60 kHz | The famous British transmitting site, home of MSF and the giant VLF station GBR. The time service moved to Anthorn in 2007 and the historic Rugby masts came down. |
| HBG | Prangins, Switzerland | LF — 75 kHz | Switzerland's time signal, switched off at the end of 2011 once DCF77 and others covered the same listeners. |
| OMA | Liblice, Czechoslovakia | LF — 50 kHz | A long-running Central European standard-frequency station, closed in 1995. |
| VNG | Llandilo, Australia | HF | Australia's standard time and frequency service, shut down at the end of 2002. |
| JJY (HF) | Japan | HF — 2.5, 5, 8, 10, 15 MHz | Japan's original shortwave time service (1940–2001), the world's second national time station after WWV. The 2.5 and 15 MHz channels closed in 1996; the remaining 5, 8, and 10 MHz signed off on March 31, 2001 when the longwave JJY stations took over — see the feature above. |
| Omega | worldwide (8 stations) | VLF — ~10–14 kHz | A global VLF navigation network whose ultra-stable signals were also used for timing; shut down in 1997 as GPS took over. |
| Loran-C | U.S. & worldwide | LF — 100 kHz | The pulsed navigation system that doubled as a precise frequency reference; the U.S. chains were shut down in 2010, again in GPS's favor. |
Back to the broadcasters: Shortwave from America: U.S. International Broadcast Stations, Past and Present · AM Broadcast Band trivia.
Sources: the NIST Time and Frequency Division (WWV, WWVH, WWVB pages), Wikipedia, the National Research Council of Canada, Germany's PTB, the UK's NPL, and standard amateur-radio time-and-frequency references. Compiled by N6JET as a noncommercial hobby reference. Questions or corrections? Email chris@n6jet.com.