Radio beginners often ask questions about CTCSS (Continuous Tone Controlled Squelch System) , thinking that they are vague and difficult to grasp. So today we will talk about what CTCSS is.

CTCSS is a technology that adds frequencies lower than the audio frequency (67Hz-254.1Hz) to the audio signal and transmits it together. The purpose is to check whether the signal is legal and whether to respond to the signal.

There is no need for CTCSS when two handheld walkie talkies are communicating directly with each other in a low interference, good environment. But for repeaters, CTCSS becomes very important: repeaters are often powerful, deployed at high altitudes and have a wide coverage area.

To make it easier for the repeater to decide which signals to relay, we can do so by means of CTCSS.

In fact, FRS(Family Radio Service）radios can be set to receive CTCSS, just like repeaters. If you set the receive CTCSS to 88.5, your radio will indicate that it is receiving even if someone else is transmitting on the same frequency, but you will not hear any signal. This is because the CTCSS is not correct. So, if you are connected to someone on a direct frequency and there is an interfering signal next to you, consider setting both transmit and receive CTCSS together. This way, when you are not connected, you can avoid the noise from the radio's unrelated signal.