Continuous-Tone-Coded-Squelch-System

Continuous Tone-Coded Squelch System

The Continuous Tone Coded Squelch System, commonly referred to as CTCSS, has been in used in the land mobile radio arena from the late 1960’s. It is known by a number of different trade names such as Private Line® (PL) by Motorola, Channel Guard® (CG) by General Electric and generically as tone squelch.

It is a use of sub-audible tones that are transmitted along with the speech portion of the transmission which allows more than one agency (or fleet) to use the same radio frequency without causing undue interference to another agency on the that frequency. Receivers for agency XYZ are set to only open their audio squelch when the proper sub-audible frequency tone is part of the transmission.

Today the sharing of frequencies by agencies is less common than it once was, CTCSS is more commonly used by repeater systems to prevent noise or interference from causing the repeater squawk obnoxiously, and by receivers as an extra measure of squelch (for instance, to prevent engine noise from breaking squelch).

The land mobile industry started with some 38 sub-audible frequencies this has increased over the years to the more generally accepted 50. There is no generic standard tone number assignment or code letter to go with a particular tone; however, below is a chart of the commonly accepted 50 tones used at this time.

In addition to the standard tones, some manufacturers have made available additional tone frequencies specific to their own products, but not available to products from other manufacturers.

Standard CTCSS Tones

CTCCS
Tone
Motorola
Code
RELM
Code
Wolfsburg
Code
NoneNone0000
67.0XZ0011
69.4WZ039none
71.9XA0022
74.4WA0033
77.0XB0044
79.7WB0055
82.5YZ0066
85.4YA0077
88.5YB0088
91.5ZZ00911
94.8ZA01012
97.4ZB01113
100.01Z01214
103.51A01315
107.21B01416
110.92Z01517
114.82A01618
118.82B01721
123.03Z01822
127.33A01923
131.83B02024
136.54Z02125
141.34A02226
146.24B02327
150.0noneSee Notenone
CTCCS
Tone
Motorola
Code
RELM
Code
Wolfsburg
Code
151.45Z02428
156.75A02531
159.8none040none
162.25B02632
165.5none041none
167.96Z02733
171.3none042none
173.86A02834
177.3none043none
179.96B02935
183.5none044none
186.27Z03036
189.9none045none
192.87A03137
196.6none046none
199.5none047none
203.5M103238
206.58Z048none
210.7M2033none
218.1M3034none
225.7M4035none
229.19Z049none
233.6none036none
241.8none037none
250.3none038none
254.10Z050none
  • Note: 150.0 is the standard tone used by military radios in the 30-88 MHz band.

Non-Standard CTCSS Tones (Kenwood)

105.4
109.1
129.6
134.2
138.9
143.8
148.8
150.0
159.5
165.1
165.5
170.9
171.3
176.9
183.1
189.5
198.2
213.8
221.3
237.1
245.5

Sound Card Decoding Programs

These programs will display the a detected CTCSS tone when connected to the audio output of a radio receiver.

Leave a Reply

Your email address will not be published. Required fields are marked *

*