In the function and features column of the walkie-talkie product introduction, you can always see English terms such as CTCSS, CDCSS, DCS, DTCS, QT, DQT, PL, TPL and DPL, or the Chinese names are sub-audio, digital sub-audio, etc. Audio, private line, digital private line, sub-audio codec, digital sub-audio codec, etc., although the names are different, all indicate that the machine has the function of sub-audio signaling format, but each manufacturer has a different name.

Sub-audio signaling is divided into two types, one is called sub-audio and the other is called digital sub-audio. The English name of sub-audio signaling is Continuous Tone Controlled Squelch System? which means continuous single tone coding squelch system. It is a coding recognition signaling technology that adds a single tone frequency (67-250.3HZ) lower than the voice frequency to the audio signal and transmits it together. Because its single tone frequency is lower than the voice frequency of 300HZ, it is called For sub-audio technology. Kenwood uses QT as the abbreviation of sub-audio, while Motorola calls this technology the PL signaling standard. PL (Private Line Codes) means private line coding, referred to as private line for short. The essence of PL signaling is CTCSS sub-audio signaling. Motorola only uses the function of private confidential line to represent this technology.

The English name of digital sub-audio (Coutinus Digital Controlled Squelech System), its Chinese meaning is Continuous Digital Coding Squelech System, referred to as DCS or DTCS. DQT also stands for Digital Sub-Audio, while Motorola calls it DPL (Digital Private Line). Digital sub-audio has the same function as sub-audio, the difference is that it is transmitted together with the audio signal in a digital encoding method. CTCSS and DCS both belong to international signaling standards. The frequency range of CTCSS is from 67.0HZ-250.3HZ***. There are 38 standard codes. Each code from 01 to 38 has a corresponding frequency. For example, the corresponding frequency of code 01 is 67.0HZ. The code of Motorola PL private line is expressed in English and numbers. For example, if the frequency is 67HZ, the English code is "XZ". In addition to the standard codes, there are also some non-standard sub-audio codes. Each manufacturer selects audio frequencies below 300HZ according to different situations. For example: Motorola's GP88 walkie-talkie has 40 groups of codes, Marantz's HX290 and Icom's IC-V8 have 50 groups of codes, Kenwood's TK-K2AT? It is 37 sets of standard codes + 97.4M non-standard codes. DCS digital sub-audio generally has 104 groups of codes, but there are a few models with more. For example, the DCS code of the IC-V8 machine is 104×2 groups.

The purpose of using sub-audio technology in the design of walkie-talkies is to avoid mutual interference between different users and avoid listening to irrelevant calls and interference signals. Because it can prevent voice and signaling interference from other users on the same channel, it is also called Tone Lock. When the transmitter of the walkie-talkie sends a voice signal, the transmitter continuously sends out a sub-audio continuous signal, which is modulated and transmitted on the same channel. When the receiver receives the carrier signal and the sub-audio signal, it performs mediation. The sub-audio signal is input to the CPU through filter shaping for decoding, and is compared and identified with the preset CTCSS (DCS) code of the machine to determine whether to turn on the squelch circuit. Only when the sub-audio code is the same, the audio output of the squelch circuit can be turned on. Sound is emitted through the speakers. Therefore, it can prevent useless voice and other signaling interference from other users in the private channel. So it can be said that it is a signaling identification system that improves the communication network's ability to resist external interference and solves the problem of non-network users accessing the network through sub-audio (digital sub-audio) signaling encoding and decoding. At the same time, CTCSS (DCS) has a selective calling function. It uses continuous single tone coding (digital coding) to carry out selective calling, and it is always carried out simultaneously with the transmission of voice signals. It is currently the most effective selective calling method. The main caller only needs to press PTT to make a group call or all call, and there is no need to press the button to hang up after the intercom call is over. It is much simpler, more convenient and faster than manually coded selective calling (DTMF) through telephone interconnection.

The technical index requirements of CTCSS (DCS) are relatively high and should comply with the standards of the Electronics Industry Association (EIA). Generally, the sub-audio frequency stability error is required to be less than ±1%. The standard sub-audio single tone deviation is: 0.5KHZ ±20%, the standard voice tone deviation: 3KHZ, the maximum frequency deviation: 5KHZ; single tone squelch sensitivity: in the receiver It can work reliably when the output signal-to-noise ratio is 8db. Some technologies of DCS and CTCSS are similar. Digital sub-audio coding is a binary signal that changes DC according to the sub-audio rate. The biggest difference between it and CTCSS is that it can automatically send out a 134HZ tone after each transmission as a "closing code" (a way to suppress noise tailing) ). DCS has faster encoding and decoding speed and lower bit error rate than CTCSS. At the same time, its group code reaches 104, allowing it to have more users in the same channel. Obviously DCS is more advanced than CTCSS, and of course it is more technically difficult. Among domestic aircraft, not many DCS technologies are mature enough to pass the test.

Sub-audio (digital sub-audio) technology has been widely used in walkie-talkie design, thereby improving the overall level of walkie-talkies.