WWV: the time signal from Fort Collins on 10 MHz

What you hear

Tune to 10000 kHz in AM and the first thing you notice is the tick: a short click every second, dry and metronomic. In the last seconds of every minute a male voice says "At the tone, fourteen hours twenty-five minutes, Coordinated Universal Time", and then a longer tone marks the minute exactly. Between the announcements there is usually a steady audio note, 500 Hz in one minute and 600 Hz in the next, and a few minutes of every hour are left silent apart from the ticks. Two ticks per minute are dropped on purpose, the 29th and the 59th.

The minutes are not all alike. The start of the hour gets a longer, higher tone. In minute 18 the station reads the geophysical alert: solar flux, geomagnetic activity, the state of the ionosphere, worth a listen if you care about propagation. Other fixed minutes carry marine storm warnings for the Atlantic and the Pacific and a short report on the health of GPS. Under the audio runs a slow binary time code on a 100 Hz subcarrier, inaudible but visible on a waterfall.

Who transmits and why

WWV belongs to NIST, the National Institute of Standards and Technology, and transmits from a field north of Fort Collins, Colorado, its home since 1966. The callsign is far older, one of the oldest still in use in the United States. The purpose is plain: put the national standard of time and frequency on the air so that anyone with a receiver can set a clock or check an oscillator by it. Before satellite timing was everywhere, laboratories and broadcasters zero-beat their equipment against this carrier.

The same programme goes out at once on 2500, 5000, 10000, 15000 and 20000 kHz, so that at least one frequency gets through at any hour; 10 MHz is the all-rounder, usable across North America by day and far beyond it after dark. WWV has a sister, WWVH on Kauai in Hawaii, on the same frequencies except 20 MHz, with a female voice that announces a few seconds before the Fort Collins male voice. Where both are heard you get two announcements in a row.

When and where to listen

From anywhere in the United States or Canada, 10 MHz WWV is a sure thing, heard like a local station. From Europe it is a catch rather than a given: the best chance comes from late evening until a few hours after European dawn, when the Atlantic path is dark, and 10 or 15 MHz are the frequencies to try. The frequency is shared with other time stations: BPM in China sits on exactly 10000 kHz as well, and from a receiver in Asia or eastern Europe the voice at night may be Chinese rather than English, sometimes both, with the two sets of ticks slightly out of step.

AM is the natural mode, because the signal is ordinary amplitude modulation with a full carrier. If noise or another station sits on top, switching to USB or LSB picks one sideband and often cleans things up, and a narrow CW filter on the carrier itself shows how steady the frequency really is.

In ShackDeck

Station catalogue → Time signals → WWV 10 MHz. The program chooses a public receiver that covers 10 MHz and hears the station, tunes it to 10000 kHz in AM and shows the waterfall: the carrier is a bright line, the ticks a row of dots beside it. You need no receiver, antenna or account of your own. The catalogue also lists WWV on 15 MHz for the day and on 5 MHz for the night.