CTCSS is generally divided into CTCSS and DCS. So what is CTCSS? In radio communication, CTCSS is used to reduce the interference of oneself to receive calls from other customers.

    What is CTCSS? The full name of analog subtone CTCSS is Continuous Tone-Coded Squelch System, a technique for attached frequencies below the audio frequency (67Hz-257Hz) that are transmitted together in an audio signal. When CTCSS is enabled, the station will attach the CTCSS signal to the normal audio signal and transmit it together. The frequency of the CTCSS is not recognized by the human ear, but the repeater can recognize it. This allows the repeater to accept only the audio signal with a CTCSS signal and not the signal without a CTCSS, thus preventing interference. In addition to the fact that the transmitting subtone of the two way radio must be the same as the receiving CTCSS of the trunk when connecting to the trunk, the subtone has other functions. In fact, when it comes to relaying, it may not be easy for beginners to understand, but let's go straight to direct mode here. In direct mode, two interphones are directly connected without trunks. At the same time, CTCSS (DCS) has the function of selecting calls, using continuous single audio encoding (digital encoding) to select calls, and always simultaneously with the transmission of voice signals is the most effective way to select calls. As long as the main call press PTT, it can make a group call or a all call. When the intercom call is over, there is no need to press a button to hang up. It is much simpler, more convenient and faster than DTMF. 

    CTCSS in repeater stations Subaudio is commonly used in relay communication and subaudio packet communication. As the main equipment of long-distance communication - base station, its receiving frequency is easily subject to some interference, such as harmonic interference, illegal users outside the network interference and so on. In order to ensure the normal operation of radio communication, it is necessary to set a threshold for the receiving frequency of the base station to intercept useless signals, such as the above mentioned subaudio threshold.  What is   DCS? CTCSS is an analog system.A supplier developed what became the digital coded squelch (DCS) system, also known as the digital Private Line (DPL). The generic name is CDCSS (Continuous Numerically coded Squelch System). CTCSS and DCS are also known by other names, including CDCSS, P, and DPL, but the formal terms are CTCSS and DCS. They both have the same function and work in a similar way.

    Despite the CTCSS, it can actually be heard, especially if the subtone is set at the high limit (around 250Hz), or if the low frequency response of the receiver is better. Therefore, when we set the CTCSS, we try to set it as low as possible to avoid unnecessary interference. Another subtone is DCS(Digital Coded Squelch), which is a CDCSS. It has 104 subpoints and is more advanced. It is coded digitally before speech and before the end of transmission. This subtone can only be transmitted and received at the same time (for example: it cannot be set to transmit but not receive). Misunderstanding: When transmitting subtone, the receiver can only receive it if it is set to subtone reception. In fact, the opposite is true.