Question T2B02
From subelement T2 - T2B
What term describes the use of a sub-audible tone transmitted along with normal voice audio to open the squelch of a receiver?
Why is this correct?
CTCSS (Continuous Tone-Coded Squelch System) is correct because it specifically describes sub-audible tones transmitted continuously with voice audio to open receiver squelch. Carrier squelch opens on any signal presence, tone burst is a brief signal for repeater access, and DTMF uses audible tone pairs for commands rather than sub-audible squelch control.
Memory tip
Remember the key distinction: sub-audible means you can't hear it during normal operation. CTCSS runs continuously underneath your voice, while DTMF produces audible beeps you actually hear. This pattern appears in many repeater access questions.
Learn more
CTCSS operates as a continuous 'permission slip' that rides along with your transmission at frequencies below normal hearing range (67-254 Hz). This sub-audible tone must match the repeater's programmed tone exactly, or your signal won't activate the repeater's receiver circuitry. Understanding this concept is essential for practical repeater operation, as most repeaters use CTCSS or DCS to prevent interference from distant stations and unauthorized access.
Think about it
Why do you think repeaters require sub-audible access tones rather than just responding to any strong signal on their input frequency?