Digital Coded Squelch

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Digital coded squelch (DCS) ( English for "digital coded squelch ") is a selective call, the formation of user groups on a common carrier frequency in the radio possible. The functional principle is identical to that of CTCSS , but the technical implementation is fundamentally different.

DCS signals

The identifiers of the individual DCS codes are:

023 025 026 031 032 036 043 047 051 053
054 065 071 072 073 074 114 115 116 122
125 131 132 134 143 145 152 155 156 162
165 172 174 205 212 223 225 226 243 244
245 246 251 252 255 261 263 265 266 271
274 306 311 315 325 331 332 343 346 351
356 364 365 371 411 412 413 423 431 432
445 446 452 454 455 462 464 465 466 503
506 516 523 526 532 546 565 606 612 624
627 631 632 645 654 662 664 703 712 723
731 732 734 743 754

Simplified functional description

Example radio

For the duration of each transmission, the transmitted voice is backed up by one of 52 possible identifiers in the form of a digital data stream. Unlike the conventional squelch, which switches on the receiver's loudspeaker when each signal is received , when DCS is used, it is only activated if the data stream is recognized with one of the 52 possible identifiers specified in advance. In this way, the recipient only receives those messages that have been provided with the identifier expected by a sender. The data stream transmitted simultaneously with the voice is made inaudible to the user in the receiver. Since the corresponding signal lies outside the audio frequency range used for speech transmission, it can be filtered out simply and effectively.

In this way, individual devices could in principle also be addressed by using the identifier expected from them when they are sent. In fact, however, much simpler and more flexible systems with larger address spaces, i.e. a larger number of individually addressable radio devices, such as 5-tone call , DTMF and the technologies MODAT , MDC-1200 and Quik Call are available.

Practical use

In practice there are two areas of application for DCS:

Avoidance of background noises

The loudspeaker is only switched on when a desired transmission is received and no longer due to interference signals such as overreach or radiation from electrical devices. Once the receiver's loudspeaker has been switched on by an ongoing, desired transmission or transmission with the expected DCS identifier, it is of course not protected as such against further interruptions or disturbances.

Creation of user groups

If, for example, a road construction company and a taxi company in a big city necessarily share the same radio frequency, because the number of users across the city simply means that there is not a separate frequency for each company, they will hardly be interested in the other’s messages. If the two companies now use a different DCS ID, the radio devices of the taxi drivers remain silent when additional material is ordered on the construction site.

However, DCS is only suitable for blocking out unwanted transmissions. If, for example, the taxi company transmits on the common frequency, this is occupied and a simultaneous transmission by another participant would cause disruptions - regardless of whether it is a different taxi driver with the same or the contractor with a different DCS ID acts. However, since the radio devices of the other participant remain mute, the only visual indicator that can be seen is whether the common frequency is free, i.e. whether he would not disturb his co-users. For this reason, with high-quality radio devices there is usually the option of using technical means to prevent transmissions when the frequency is already occupied (usually called “busy channel lockout” / BCLO).

No protection against unauthorized eavesdropping

When using digital coded squelch , there is absolutely no protection against eavesdropping , since signals are only suppressed at all when the DCS is activated on the receiver. If the listener deactivates this function on his radio, all transmissions will be received on the set frequency - regardless of whether they are provided with a DCS identifier or not. The same effect is achieved if the receiving device simply does not support the DCS function. In the application there is the fact that the transmit button (PTT) has to be pressed a little longer (approx. 0.5 seconds) until the group devices open the signal for the receiver. Unlike in the uncoded process, where you can speak immediately after pressing a button.

Alternative names

The method was described in 1994 in the British telecommunications standard MPT 1381 under the name Digital Coded Squelch .

However, it is known by various manufacturers of radio sets under different names:

  • Digital Private Line (DPL) is a trademark of Motorola .
  • Digital Tone Code Squelch (DTCS) is the name used by ICOM .
  • Digital Channel Guard (DCG) is the name of the technology at General Electric .
  • Digital Quiet Talk (DQT) at Kenwood

See also

Individual evidence

  1. ↑ Markus Zubler: Tables of the CTCSS, DCS, Common ID. In: freeradionetwork.ch. Retrieved June 17, 2011 .
  2. ↑ MPT 1381 CODE OF PRACTICE Digitally Coded Squelch Signaling (DCSS) system for use in the Land Mobile Services. (PDF; 44 kB) In: Ofcom's official website . 1996, accessed June 17, 2011 .