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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.

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.

Contents

Standard CTCSS Tones

Tone Motorola Code RELM Code Wolfsburg Code Tone Motorola Code Wolfsburg Code RELM Code
None None 000 0 167.9 6Z 33 027
67.0 XZ 001 1 173.8 6A 34 028
71.9 XA 002 2 179.9 6B 35 029
74.4 WA 003 3 186.2 7Z 36 030
77.0 XB 004 4 192.8 7A 37 031
79.7 WB 005 5 203.5 M1 38 032
82.5 YZ 006 6 210.7 M2 none 033
85.4 YA 007 7 218.1 M3 none 034
88.5 YB 008 8 225.7 M4 none 035
91.5 ZZ 009 11 233.6 none none 036
94.8 ZA 010 12 241.8 none none 037
97.4 ZB 011 13 250.3 none none 038
100.0 1Z 012 14 69.4 WZ none 039
103.5 1A 013 15 159.8 none none 040
107.2 1B 014 16 165.5 none none 041
110.9 2Z 015 17 171.3 none none 042
114.8 2A 016 18 177.3 none none 043
118.8 2B 017 21 183.5 none none 044
123.0 3Z 018 22 189.9 none none 045
127.3 3A 019 23 196.6 none none 046
131.8 3B 020 24 199.5 none none 047
136.5 4Z 021 25 206.5 8Z none 048
141.3 4A 022 26 229.1 9Z none 049
146.2 4B 023 27 254.1 0Z none 050
151.4 5Z 024 28 150.0 none none See Note
156.7 5A 025 31
162.2 5B 026 32


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.

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