Deep Dive: T2B02
The correct answer is D: CTCSS. CTCSS (Continuous Tone-Coded Squelch System) is a sub-audible tone (typically below 300 Hz) that's transmitted along with normal voice audio to open the squelch of a receiver. This allows repeaters and receivers to only respond to signals that include the correct CTCSS tone. CTCSS tones are inaudible to human ears but are detected by the receiver's squelch circuit. When a repeater is configured with CTCSS, it only retransmits signals that include the correct tone. This helps filter out interference and unwanted signals. Common CTCSS tones range from 67.0 Hz to 254.1 Hz, with 100.0 Hz, 103.5 Hz, and 107.2 Hz being very common.
Why Other Answers Are Wrong
Option A: Incorrect. Carrier squelch opens the squelch based on signal strength, not a sub-audible tone. It doesn't use tones at all. Option B: Incorrect. Tone burst is a brief audible tone used for repeater access, not a continuous sub-audible tone. Option C: Incorrect. DTMF (Dual-Tone Multi-Frequency) uses pairs of audible tones for signaling, not a single sub-audible tone.
Exam Tip
Sub-audible tone = CTCSS. Remember: CTCSS uses a continuous sub-audible tone (below 300 Hz) that you can't hear but the receiver detects to open squelch.
Memory Aid
**S**ub-**A**udible **T**one = **C**TCSS (think 'SAT = CTCSS')
Real-World Example
Your local repeater requires a CTCSS tone of 100.0 Hz. You program your radio to transmit this tone along with your voice. When you transmit, the repeater detects the 100.0 Hz tone (which you can't hear) and opens its squelch to retransmit your signal. Without the correct CTCSS tone, the repeater won't respond, even if your signal is strong enough.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T2B
Reference: FCC Part 97.205
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T2B topic.