WWV is a clock for 59 minutes and an experiment for one
2026-07-24 · EA5IYR
WWV has been on the air since 1920, which makes it the longest continuously broadcasting radio station in the world. It transmits from Fort Collins, Colorado on 2.5, 5, 10, 15 and 20 MHz, and what it broadcasts is the time: ticks every second, tones, and a voice announcement every minute.
That sounds like the least interesting signal on shortwave. It is one of the most useful. Why a time station is a propagation instrument
Every other signal you receive has two unknowns: what the transmitter did, and what the path did to it. You cannot separate them.
WWV removes the first unknown entirely. Its frequency is exact by definition. Its timing is exact by definition. Its power is published and constant — 10 kW on 5, 10 and 15 MHz, 2.5 kW on 2.5 and 20 MHz.
So everything that is different about the signal when it reaches you was done by the ionosphere. Whether 20 MHz is audible tells you whether the band is open. Comparing 5 against 15 tells you where the usable frequency ceiling currently sits. Doing that at the same time each day, over months, tracks the solar cycle from your own back garden. Minute 8
Since November 2021, WWV has carried an experimental signal during the eighth minute of each hour, run jointly with HamSCI, a community of amateur radio operators doing ionospheric research.
The point is to give researchers — and anyone else — a precisely known waveform, transmitted at a precisely known instant, so that distortions in what arrives can be measured rather than guessed at. It turns a national time service into a shared scientific reference that thousands of receivers can observe simultaneously.
It is a genuinely unusual arrangement: a government metrology institute donating one minute in sixty to distributed volunteer science. It nearly did not survive
In 2019 a federal budget proposal would have eliminated funding for WWV, along with its sister stations WWVH in Hawaii and WWVB, the low-frequency station that sets radio-controlled clocks across North America.
The proposal drew sustained objections from the amateur radio community and from people who pointed out how much infrastructure quietly assumes those signals exist. Funding survived, and the stations are still transmitting. It is worth remembering that this was a decision somebody made, not a law of nature. What to do with it
Park a receiver on 10 MHz. Note whether you hear it, and how strongly, at the same hour each day. Then try 15 and 20 MHz.
Within a couple of weeks you will have a record of your own path to Colorado, and a much better instinct for when to bother looking for weak signals elsewhere — the kind of instinct that makes chasing a numbers station a matter of timing rather than luck.
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Sources: NIST — WWV, IEEE Spectrum — federal radio stations in danger of shutdown, ARRL — concern over WWV/WWVH shutdown proposal.