Home User Tutorial Understanding Sub-Audio Signaling in Two-Way Radios

Understanding Sub-Audio Signaling in Two-Way Radios

by Chen, Robin

When using walkie-talkies, do you often have questions like, what is Sub-audio and what functions does it have? This blog will help you understand it.

The English term for sub-audio signaling is Continuous Tone Controlled Squelch System (CTCSS), which means a continuous single-tone coded squelch system. It’s a technology that encodes recognition signals by adding a single-frequency tone (ranging from 67 to 250.3Hz) below the audio frequency in the audio signal. It’s called sub-audio because its single frequency is below the 300Hz audio frequency.

Digital sub-audio, known as Continuous Digital Controlled Squelch System (CDCSS), stands for a continuous digital coded squelch system.

What is the sub-audio function in two-way radios?

1. Prevent unauthorized users from accessing the channel.
2. It has strong anti-interference capabilities, particularly effective in relay communication systems to protect the relay station from interference signals.
3. Enables frequency reuse in localized areas, improving frequency utilization and enabling frequency sharing.
4. It allows for selective calling of different groups, broadcasting, and other calling functions, making it practical and easy to use.

Sub-audio signaling involves both transmitting and receiving sub-audio.

Generally, to access a relay station, transmission it is used to open the relay. The relay station itself uses “receiving sub-audio,” rejecting signals without it. Incoming signals to the relay station may or may not carry it.

Similarly, for reception, to exclude unwanted signals, receiving it can add. This way, two (or several) radios can use agreed-upon it to eliminate external interference signals.

Retevis has many digital radios and analog radios, I prefer RT29 because it has a DMR version RT29D, allowing you to have both experiences.

Related Blog: Retevis RT29D: Get an upgraded DMR experience (twowayradiocommunity.com)

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