Definition
A VHF radio channel arrangement in which adjacent communication frequencies are separated by 25 kilohertz (0.025 MHz). Within the aviation VHF voice band (118.000–136.975 MHz), this spacing yields 760 usable channels, expressed in increments such as 118.000, 118.025, 118.050, and so on.
Plain English
It means each radio channel sits 25 kilohertz away from the next one. Tuning steps go up by 0.025, like 118.000, 118.025, 118.050.
Context Anchor
Seen when reading about aircraft communication radios and when tuning or checking which frequencies a radio can select.
Derivation
Hertz (Hz) is the unit for cycles per second, named after physicist Heinrich Hertz. Kilo- means thousand, so 25 kHz is 25,000 cycles per second. 'Spacing' here simply means the gap between one channel and the next on the dial.
Why Pilots Care
Provides enough distinct channels for ATC, flight service, and air-to-air use without interference.
Intuition Check
“Spacing” does not mean physical distance between radios or antennas here. It means the frequency gap between one usable radio channel and the next.
Example Sentence 1
His older comm radio used 25 kHz spacing, so he couldn't tune the 8.33 kHz frequency the European controller assigned.
Example Sentence 2
Older aircraft radios limited to 50 kHz spacing could not access the additional channels now available with 25 kHz spacing.