Definition
A second, ready-to-use VOR ground transmitter that automatically takes over signal transmission if the primary transmitter fails or is taken out of service for maintenance. While the standby is on the air, the station's identification is replaced by a continuous tone or by the word 'TEST' in Morse code, indicating the signal should not be used for navigation.
Plain English
A backup transmitter at a VOR ground station that switches on when the main one goes down. While it's running, the station stops sending its normal Morse code identifier so pilots know not to navigate by it.
Context Anchor
Seen in discussions of VOR ground-station equipment and how the station maintains reliable navigation service.
Derivation
Standby' comes from the nautical and military sense of being ready to act on short notice -- on hand, but not currently in use. A standby transmitter is exactly that: installed, powered, and waiting to take over.
Why Pilots Care
Maintains continuous navigation guidance so a pilot does not lose the VOR signal during a transmitter failure.
Intuition Check
Do not read “standby” as simply “inactive” or “unimportant.” Here it means backup equipment kept ready to take over when the main transmitter cannot do the job.
Example Sentence 1
When the pilot tuned the VOR and heard a continuous tone instead of the Morse identifier, she realized the standby transmitter was in use and selected a different navaid.
Example Sentence 2
Before departure the pilot confirmed that both the primary and standby transmitters at the VOR were operational.