Continuous Tone Coded
Squelch System (CTCSS)




Continuous Tone Coded Squelch System (CTCSS) is a feature in most conventional analog radios, using sub-audible tones to allow multiple groups of users to communicate on the same frequency (channel) without receiving radio traffic from each other; and to improve radio operation in high RF noise, interference and congested areas. The feature transmits a tone between 67 Hz to 254 Hz (below human hearing range) along with the voice traffic. The receiving radio may be programmed to only respond to signals transmitting the desired tone frequency.

Digital Coded Squelch (DCS) is a digital form of CTCSS. A third type of squelch system, called Selective Calling (SelCall) is used in some business radios, but is not used in Ham radios. Note that none of these squelch systems are used in digital radios.

CTCSS is also known by a number of other terms which are registered trademarks of individual manufacturers. Among them are Private Line (PL), owned by Motorola; Channel Guard (CG), owned by GE/Ericsson/Harris; and Quiet Tone (QT), owned by Kenwood.

Some Family Radio Service (FRS) radio manufacturers use other terms for CTCSS, including Privacy Code and Sub-Channel.

Below are tables of the tone frequencies used for CTCSS and the codes used for DCS.


CTCSS Tone Frequencies (Hz)
67.0
69.3
71.9
74.4
77.0
79.7
82.5
85.4
88.5
91.5
94.8
97.4
100.0
103.5
107.2
110.9
114.8
118.8
123.0
127.3
131.8
136.5
141.3
146.2
151.4
156.7
159.8
162.2
165.5
167.9
171.3
173.8
177.3
179.9
183.5
186.2
189.9
192.8
196.6
199.5
 203.5 206.5
210.7
218.1
225.7
229.1 233.6
241.8
250.3
254.1



DCS Codes
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
654
662
664
703
712
723
731
732
734
743
754