Long radio waves, typically operating between 30 kHz and 300 kHz with wavelengths stretching from 1 to 10 kilometers, serve a surprisingly wide range of purposes. Their defining advantage is reach: they follow the curve of the Earth rather than shooting off into the sky, letting them travel up to 2,000 kilometers from a single transmitter and pass through obstacles that block higher-frequency signals.
How Long Radio Waves Travel So Far
Most radio signals travel in straight lines, which means they’re blocked by mountains, buildings, and the horizon itself. Long radio waves behave differently. Their enormous wavelengths allow them to diffract over obstacles like mountain ranges and hug the Earth’s surface, a behavior called ground wave propagation. The signal loses less energy as it travels across the ground compared to higher frequencies, which is why a single longwave transmitter can blanket an entire region without relay towers or satellites.
This ground-hugging ability also means longwave signals pass easily through non-metallic structures like walls and roofs. That property turns out to be critical for one of their most common everyday uses.
Keeping Clocks Accurate
If you own a “radio-controlled” or “atomic” wall clock, it almost certainly sets itself using a longwave signal. Dedicated time signal stations around the world broadcast the exact time on low frequencies, and these signals are strong enough to reach receivers indoors with tiny built-in antennas.
In the United States, a station called WWVB in Fort Collins, Colorado broadcasts continuously at 60 kHz with 50 kilowatts of power. That signal is strong enough during nighttime hours to reach all 50 states. It’s locked to a cesium atomic clock that stays synchronized with Coordinated Universal Time (UTC). The station encodes the time by briefly reducing its signal power once per second: a short dip means a zero, a longer dip means a one, and an even longer dip marks the boundary of each data frame.
Inside a radio-controlled clock, a small 60 kHz crystal acts as a permanently tuned receiver, picking up this binary stream and feeding it to a processor that corrects the clock’s timekeeping. Similar stations operate worldwide: DCF77 in Germany at 77.5 kHz, MSF in the United Kingdom at 60 kHz, JJY in Japan at 40 and 60 kHz, and BPC in China at 68.5 kHz. Together, these stations give billions of consumer clocks and watches a free, reliable time reference that works better indoors than GPS signals do.
Communicating With Submarines
Seawater is nearly opaque to most radio frequencies, but very low frequency (VLF) signals in the 3 to 30 kHz range can penetrate beneath the surface. This makes them one of the only ways to reach a submarine without forcing it to surface or raise an antenna above the waterline. Military organizations, particularly those managing nuclear submarine fleets, maintain massive VLF transmitter networks for exactly this purpose. The signals carry digital messages that provide global coverage and reliable performance even in heavy atmospheric noise.
The tradeoff is bandwidth. These ultra-long wavelengths can only carry very small amounts of data, so messages to submarines are brief, often just coded instructions. But for a submarine trying to stay hidden, receiving even a short message without surfacing is invaluable.
Navigation and GPS Backup
For decades, longwave signals provided the backbone of radio navigation. Non-directional beacons (NDBs), operating in the 200 to 400 kHz range, transmit signals in all directions from a ground station. An aircraft equipped with an automatic direction finder (ADF) picks up the signal and determines which direction it’s coming from, allowing the pilot to fly toward or away from the beacon. These served as primary short-distance navigation aids for much of aviation history.
NDBs are now being phased out in favor of GPS-based navigation. The FAA has been systematically decommissioning them, including a plan to replace 51 of 59 NDBs in Alaska with GPS-based route structures. But that transition has also raised a concern: GPS signals come from satellites and can be jammed or spoofed.
That vulnerability has given longwave navigation a second life. Enhanced LORAN (eLORAN), which evolved from the older Loran-C system, operates at 100 kHz and serves as a ground-based backup to satellite navigation. South Korea has tested differential eLORAN for precision port navigation, and the New York Stock Exchange has tested it as a backup timing source. China is actively building new eLORAN stations in locations like Dunhuang, Korla, and Nagqu, with operations expected to begin in 2026. The combination of eLORAN and satellite navigation has become a widely adopted safety model internationally.
Broadcasting
Longwave AM radio broadcasting still exists, though it has shrunk considerably in the internet age. A handful of stations remain active, mostly in Europe, North Africa, and Central Asia. BBC Radio 4 broadcasts on 198 kHz in the United Kingdom. Polskie Radio Program I uses 225 kHz in Poland. Mongolia’s MNB Radio 1 operates on multiple longwave frequencies (164, 209, and 227 kHz) to cover its vast, sparsely populated territory. Médi 1 broadcasts from Morocco at 171 kHz, and stations in Algeria, Romania, Turkey, Italy, Sweden, and Georgia also remain on the air.
The appeal of longwave broadcasting is simple: a single transmitter can cover an enormous geographic area, including remote regions where FM signals and internet infrastructure don’t reach. Audio quality is lower than FM, but for news, talk radio, and basic programming, it remains a practical solution in places where the alternatives are expensive or nonexistent.
The Cost of Going Long
The same physics that make long radio waves useful also make them expensive to generate. An efficient antenna needs to be a significant fraction of the wavelength it transmits. For a signal at 60 kHz, the wavelength is 5 kilometers, which means practical longwave antennas are massive structures. Military VLF stations use antenna arrays strung between towers that can exceed several hundred feet in height, supported by miles of cable. Even amateur radio operators working at 3.5 MHz (a much higher frequency than true longwave) need towers exceeding 120 feet for serious long-distance work.
This infrastructure requirement is why longwave transmitters tend to be government-operated or tied to national broadcasting services. Building and maintaining them costs far more than a typical FM or cellular tower, which limits longwave to applications where its unique propagation advantages justify the investment.