ARRL Technician Practice Exam 2025 – Complete Prep Guide

The term used to describe the use of a sub-audible tone transmitted with normal voice audio to open the squelch of a receiver is CTCSS, which stands for Continuous Tone-Coded Squelch System. This technology allows operators to communicate on a shared frequency without unintentionally receiving transmissions from other stations that are not using the same sub-audible tone. When a station wants to transmit, it sends the voice audio along with a low-frequency tone that is inaudible to humans but can be detected by the receiver. The receiver is set to "open" or unmute when it detects the specific tone, allowing for clearer communication and minimizing interference from unwanted signals.

In contrast, the other options represent different concepts: DTMF refers to Dual-Tone Multi-Frequency signaling used primarily in telephony, PL Tone typically refers to a private line or another name for CTCSS but is less commonly used in formal contexts, and DSB stands for Double Sideband, which is a modulation method unrelated to the squelch function. The terminology surrounding CTCSS is vital for understanding how operators can effectively manage their communications in crowded radio environments.