1) Airband

The VHF radio spectrum used for civil aviation is called Airband, or Aircraft band.

2) The Lower Band

The lower part of the band, from 108.000-117.950 MHz, is split into 200 channels, spaced 50 kHz apart, which is used for NAVAIDs.

3) ILS and VOR

108.000-112.000 MHz is used for ILS and terminal VORs, and 112.000-117.950 MHz used for low and high VORs.

4) The Upper Band

The upper part of the band, from 118.000-136.975 MHz, is split into 760 channels, spaced 25 kHz apart, for voice communication.

5) Transmitting in AM

Your VHF radio uses amplitude modulation, so you’re actually transmitting to ATC in AM, similar to the AM radio in your car.

6) Overriding Signals

AM transmissions allow stronger stations to override weaker ones. This means ATC can talk over a transmitting aircraft, or an aircraft with a stuck mike.

7) Capture Effect

Additionally, AM doesn’t suffer from the capture effect found in FM. Capture effect is the complete suppression of the weaker signal. When an FM radio receives signals are nearly equal in strength, or are fading independently, the receiver may switch from one to the other. This means that a nearby aircraft could inadvertently override ATC.

8) Transmission Range

A typical transmission range of an aircraft flying at 4,500 feet is about 100 miles. At 35,000 feet, it’s about 200 miles.

9) Bending Signals

VHF radio range is slightly better than line-of-sight, because the radio waves are weakly bent back toward Earth by the atmosphere. Just because you can’t see the tower or RCC you’re transmitting to, doesn’t mean you can’t reach it.