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Very High Frequency (VHF) radio is installed in many aircraft for both communication and navigation purposes. The VHF radio used for voice communication is called VHF COM, and functions as a transmitter and a receiver. Most planes have an additional VHF radio for navigation, called VHF NAV. The VHF NAV radio acts only as a receiver and is used to deliver information from ground-based transmitters to the pilot.

VHF transmissions can be disrupted or blocked by mountain ranges or other large objects. As elevation increases (as the plane rises above major obstructions) the range of the VHF signals increases accordingly:

• Below 5,000 feet, the signal range extends up to 60 nautical miles
• Between 5,000 to 10,000 feet, the signal range extends up to 90 nautical miles

Automatic relay equipment on the ground and on satellites can improve the range of VHF frequencies. A squelch control may also be added to the VHF radio to electronically filter out interference. By adjusting the squelch, pilots can fine-tune the reception to remove background noise and static.