What is sub audio?
The English abbreviation is CTCSS (Continuous Tone Controlled Squelch System), which is a technology that adds frequencies below the audio frequency to the audio signal and transmits it together. Because its frequency is below the standard audio frequency, it is called sub audio.
There are two types of sub-tones: transmitting sub-tones and receiving sub-tones. In order to be able to relay, they use transmit sub-tones so that the relay can be turned on. The relay itself uses "receiving sub-tone", and signals without sub-tone are rejected.
How to receive and transmit sub-audio?
Take the instant messaging D9000 car station as an example, press the function key on the panel, then press the right menu key, turn to find the sub-audio setting option, and press the knob to set.
What are the benefits of setting up sub-audio?
The initial use of sub-audio is to provide a directional noise suppression capability. If two people want to communicate on a frequency that is often used by people and only want to hear each other, the two people can set the same transmit sub-tone. And set the machine to only accept signals that contain the subtone in the sound. So for these two people, their machines will only sound normally when they receive a signal containing that subtone, and the machine will remain quiet after receiving other signals. In this way, relatively speaking, both people only heard the sound they wanted to hear, which played a directional noise suppression effect. For other people who have no settings, the conversation between these two people will be accepted and played normally, and it is not that other people can't hear it.
In addition, the sub-audio can also be used with a repeater. The repeater will always monitor a certain frequency when it is working, and forward the signal of that frequency to another frequency. If there is no sub-audio system for selection, the The relay station will forward all signals on this frequency, regardless of whether it is a valid voice signal. In other words, the existence of the sub-audio system greatly reduces the probability of false triggering of the repeater.