Pl Codes Private Line Codes or Ctcss Continuous Tone Coded Squelch System

Squelch Tones 101

Let's talk about Tone, Tone Squelch, CTCSS, PL, Digital Squelch, DCS, DPL or what ever you might have heard about.

CTCSS? DCS? Sub-channels? Yes, Continuous Tone Coded Squelch System. Introduced by Motorola in the early 1960s, as "Private Line" (also known as GE/Ericsson's "Channel Guard", E.F. Johnson's "Call Guard", RCA's "Quiet Channel"), known by many as simply "tone squelch". This is like a mains hum on the modulation, a constant musical note... almost as if someone is standing by you humming as you talk. The receiver can be set to only open its squelch if this tone is received. Any interference would not have the correct tone present, and so the radio would remain quiet. CTCSS was developed into a system with numerous standard tones to choose from, often 38. When CTCSS is used, the audio is filtered out below about 300Hz, so that the only audio frequency energy that ends up being transmitted between 0 and 300Hz is the CTCSS tone itself (almost always any one tone between 67 and 254.1 Hz). The tone is then sometimes called 'sub audible' because it's below the range of THEN audible voice frequencies - but it would be audible if played on full range speakers without the filtering that CTCSS radio receivers also use on receive (we can hear down to 20Hz or so).

Some  Amateur Radio Repeaters are configured, that the tone may not be transmitted only received, this allows the security of the the encode ability of your transceiver. so depending on your manufactures software it may be labeled Tone, or Encode. If the repeater is configured to transmit the same or different tone your setting may be labeled Tone Squelch, TSquelch, or Encode/Decode. The most common tone for or FRC District #5 is 103.5 CTCSS and 411DPL. This helps us from hearing other systems on the same frequency from other Florida Distracts when conditions are rolling. These stations are not "Bleeding Over" that is something completely different. They have the same rights on the frequency that you have.

DCS

DCS (Digital Coded Squelch) is digital data or code word that is transmitted with the voice audio. This data is sub-audible with most of it's energy below 300Hz. However is does have a wide bandwidth from 2 to 300 Hz. Unlike CTCSS (Continuous Tone Coded Squelch System) which uses continuous tones below 300 Hz., DCS uses digital data or code words. Each code word is unique and all code words may be used on the same channel without interference. At the end of the radio transmission and about 1/2 second before the transmitter un-keys, the radio will encode a 134 Hz tone that serves as a turn off code. The FM deviation level of DCS data should be in the range of 500 to 800 Hz.

Unlike CTCSS, DCS signal spectrum occupies considerable more bandwidth. A poor low frequency response in the transmitter or receiver may not seriously distort a single frequency tone signal but may seriously degrade a wide band signal containing multiple frequency components. The distortion risk is especially high if the frequency response delays the wide band frequency components.

DCS is operated at a low baud rate (134.4 bits per second) and because DCS may have extended periods of all ones and zeros almost all components in the transmitter and receiver chain must be coupled down to at lease 2 Hz or lower. This requirement means that certain transmitters and receivers must be modified before they are capable of DCS operation. Phase modulators, in particular, need special consideration because they theoretically are incapable of being directly modulated by dc, unlike direct FM modulation methods. Low frequency response is the primary requirement for DCS systems.

You will find that it is extremely important for the receiver and transmitter to be on frequency to achieve maximum performance of the DCS function. Errors in the transmitter and receiver frequencies show up a the discriminator output as a step function. Because of the long time constant required for the low frequency response, a step function can block the decoder momentarily. With DCS, error correction is necessary. But if too many errors occur, you may experience some blocking out of the decoder. Errors can occur because of unwanted low frequency energy. The DCS decoders can be effected by voice energy that falls below 300 Hz. Some radios do not remove this energy before transmission and can cause voice blocking of the decoder. A sub audio filter that removes this low frequency energy before the audio is re-transmitted is necessary for reliable DCS operation.

Now there are a few systems that use both the DCS and CTCSS on one side or the other and even using both.

CTCSS Encode DCS Decode - DCS Encode CCTCSS Decode - CTCSS/DCS ENCODE CTCSS/DCS Decode.

A video discussing this can be found HERE .

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

This board can be incorperated into older transeivers to use in current repeater operation. Can be istalled in radio chassis or incoperated into the Microphone if space permits.

SS-64
Microminiature CTCSS Encoder

Specifications:

Powered by 5-28 VDC, unregulated @ 6.3 ma.
Low impedance (15K ohms), low distortion adjustable sinewave output, 0 to 2V.
Frequency accuracy +/- .025 Hz maximum over -30° C to +65° C temperature range.
Start-up time less than 10 ms.
Squelch tail elimination of 175 ms reverse phase burst followed by 175 ms of no tone.
Totally immune to RF.

$28.95

Features:

Compatible with all sub-audible CTCSS systems.
Microminiature in size: .66" x 1.08" x .21" high to fit inside most handhelds.
64 tones from 33.0 Hz to 254.1 Hz, crystal controlled for high accuracy and stability.
Mini 6 position Dip Switch to select desired tones.
Multiple tone switching can be easily handled by using diodes and a single pole switch.
Built in Reverse Burst option with Transmit Time-Out Timer.
Full 1 year warranty when returned to the factory for repair.
Immediate 1 day delivery.

SS-64 Instructions  |  Application information

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