VHF — Very High Frequency

The VHF Band in Aviation

Very High Frequency covers the radio spectrum from 30 to 300 MHz, but civil aviation uses a specific slice of it — 118.000 to 136.975 MHz — for essentially all air-ground voice communication: pilots talking to ground control, tower, departure, approach and en-route ATC sectors, plus company operations frequencies and the emergency frequency 121.5 MHz. Every phase of a flight uses a different assigned VHF frequency, handed off from one controller to the next as the aircraft moves through different sectors of airspace.

Why VHF Was Chosen

VHF radio propagates largely by line of sight rather than bouncing off the ionosphere the way HF (High Frequency) does, which makes it far less prone to the long-distance interference and unpredictable propagation that plague HF communication. For air traffic control, where clarity and immediacy matter more than extreme range, that trade-off — shorter range in exchange for a clean, reliable signal — is exactly right. It's also why VHF isn't used for the very long transoceanic and polar routes where no ground station is within line of sight; those routes still rely on HF or satellite datalink instead.

Channel Spacing and Frequency Congestion

As air traffic grew, the number of aircraft trying to share a limited VHF band became a real bottleneck. Traditionally, VHF aviation channels were spaced 25 kHz apart; to fit more usable frequencies into the same band, many regions — Europe in particular — have progressively mandated 8.33 kHz channel spacing, tripling the number of available channels within the same 118–137 MHz range. This is a purely regulatory and equipment response to congestion, not a change to how VHF itself works physically.

VHF's Role Beyond Voice

VHF isn't only used for voice. ACARS (Aircraft Communications Addressing and Reporting System) and VDL (VHF Data Link) use the same band to carry digital messages between aircraft and airline operations centers or air traffic systems — automated position reports, weather requests, maintenance data, and datalink clearances that don't require a pilot to speak on the radio at all.

The Practical Limitation of VHF

Because VHF depends on line of sight, its range is fundamentally limited by the transmitter's altitude and the curvature of the earth — a ground station typically reaches an aircraft cruising at altitude out to roughly 200 nautical miles or more, but that range collapses sharply for aircraft on the ground or at low altitude, especially with terrain in the way. This is precisely why VHF ATC coverage requires a dense network of ground stations along busy air routes, rather than a handful of very powerful transmitters.