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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.

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.

Contents

Standard CTCSS Tones

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

Related Links

  • CTCSS Technical Overview
  • For the current ETSI Standard TS 103 236 Continuous Tone Controlled Signalling System (CTCSS) and Digitally Coded Squelch Signalling (DCSS) document click on the Standards tab on this page.

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