CTCSS (Continuous Tone-Coded Squelch System) is a continuous tone coded squelch or friend / foe signal identification system.

The tone coding function is necessary for dividing correspondents (users) into groups working on one radio channel. Only those correspondents who have the same CTCSS code (tone) can listen and broadcast within "their" group. For those who are not tuned to the required CTCSS code, these transmissions will be suppressed as unnecessary noise and nothing will be heard.

Continuous Tone-Coded Squelch System (CTCSS) is an access control method in radio communication systems based on the presence in the wanted signal of sound tones of a certain frequency that lie outside the modulation frequency range (out of earshot) at frequencies below 300 Hz.

During transmission, a subtone signal (below 300 Hz) of a certain frequency (determined by the CTCSS code) is sent, which, upon reception, is instantly recognized by the CTCSS squelch as "friend" or "alien". If the code is "your", then the radio station turns on for reception and reproduces the message, if "stranger", then it does not turn on and the correspondent does not hear anything.

The radio station's receiver is activated only when the specified CTCSS tone appears, for which it is programmed. CTCSS is standard on most modern radio equipment.

The number of CTCSS codes (tones) stitched into a radio station is different: from a dozen in the simplest models, it can reach 50. In radio stations, it is typically 38, in radio amateurs - 39.

Typically, frequencies below the speech signal range of 67 to 257 Hz are used.

In practice, this can be used like this (provided that the other radio channels are busy for some reason or not usable):

If one group of people must perform one type of work, the second another, etc., and they should not interfere with each other;
- some of the radios are tuned to one CTCSS code, some to another, etc .;
- the chief can manage different groups by switching the code.

CTCSS is used to organize many independent and practically non-interfering groups of subscribers on the same frequency. Practically not interfering - because only one subscriber of any of the groups can transmit something at a time, while only subscribers of the group that the transmitting subscriber belongs to will receive his message.

Different vendors refer to CTCSS differently. For example Motorola designates CTCSS as PL(Private Line - Private line), GE`s / Ericsson as CG(Channel Guard), and Kenwood as QT(Quiet Talk - Quiet conversation).

In practice, when communicating between different types of radio stations, it is better to coordinate not the subtone number, but its frequency, according to the operating instructions.

The best choice of frequencies will be not too low (due to the increase in the tone detection time) and not too high (due to conflicts with the speech signal in the cheapest models of radio stations) frequency values ​​- optimally somewhere from 120 to 200 Hz; at the same time, frequencies that are multiples of the frequency of the alternating current network (for Russia - 50 Hz) should be avoided - that is, adjacent to 100, 150 and 200 Hz.

The BAOFENG UV-5R radio station, like the vast majority of modern stations, has support CTCSS and DCS subtones or, more simply, the system of identification of friend / foe.

How to set subtone on BAOFENG UV-5R
You can set the subtone for reception and transmission through the station menu. To prevent extraneous conversations from getting into the communication of your group, close the channel to a subtone by setting the same subtone for reception and transmission for all radios in the group. There is a brief instruction for BAOFENNG, you need menu items 10 to 13. We put the same subtones everywhere CTCSS or DCS and you're done!

What is it for?
Ideal communication conditions never exist, especially in large cities where, besides you, a large number of groups of correspondents can communicate on the same frequencies. And so that they do not interfere with each other using the aforementioned subtones, you can create your own groups that will only hear the signals of radio stations entering it, and radio stations operating on the same frequency, but not included in this group, will be ignored by the station squelch.

This is especially true when working on channels of the range of which there are only eight, and there can be several dozen correspondents within the reception area of ​​the station of your group.

Having set the same subtones for transmission and reception on the radio stations of your group, you will hear only those stations that are included in the group, provided that the transmission is carried out when the frequency is free.

In modern stations, as a rule, two coding systems are used:
- CTCSS system(Continuous Tone-Coded Squelch System) is a noise reduction system encoded with a continuous low frequency signal that is mixed into the speech signal, for this, frequencies below its range from 67 to 257 Hz are used. Those. you will not even hear them in the dynamics of your station.

Not all stations indicate the real frequency of the subtone, but its number is displayed, below you will find a table by which you can determine which subtone is tuned in to another station, but this is not Baofeng

subtone frequency	1 of 38 codes	1 of 39 codes	1 of 43 codes	1 of 48 codes	1 of 50 codes
62.5	1
64.7	2
67.0	1	1	1	3	1
69.3	2	2	4	2
71.9	2	3	3	5	3
74.4	3	4	4	6	4
77.0	4	5	5	7	5
79.7	5	6	6	8	6
82.5	6	7	7	7
85.4	7	8	8	10	8
88.5	8	9	9	11	9
91.5	9	10	10	12	10
94.8	10	11	11	13	11
97.4	11	12	12	14	12
100.0	12	13	13	15	13
103.5	13	14	14	16	14
107.2	14	15	15	17	15
110.9	15	16	16	18	16
114.8	16	17	17	19	17
118.8	17	18	18	20	18
123.0	18	19	19	21	19
127.3	19	20	20	22	20
131.8	20	21	21	23	21
136.5	21	22	22	24	22
141.3	22	23	23	25	23
146.2	23	24	24	26	24
151.4	24	25	25	27	25
156.7	25	26	26	28	26
159.8	27	29	27
162.2	26	27	30	28
165.5	28	29
167.9	27	28	31	30
171.3	29	31
173.8	28	29	32	32
177.3	30	33
179.9	29	30	31	33	34
183.5	32	34	35
186.2	30	31	33	35	36
189.9	34	36	37
192.8	31	32	35	37	38
196.6	36	38	39
199.5	39	40
203.5	32	33	37	40	41
206.5	41	42
210.7	33	34	38	42	43
218.1	34	35	39	43	44
225.7	35	36	40	44	45
229.1	45	46
233.6	36	37	41	46	47
241.8	37	38	42	47	48
250.3	38	39	43	48	49
254.1	50

- DCS system(Digital Coded Squelch) is a digital selective call system. DCS is a 23-bit code sent continuously at 134.3 bits per second. This system, as a rule, is an attribute of more modern stations, is more reliable, providing better communication quality.

Below is a table of DCS tones and their correspondence

Direct DCS	Inverse DCS
23	047 i
25	244 i
26	464 i
31	627 i
32	051 i
36	172 i
43	445 i
47	023 i
51	032 i
53	452 i
54	413 i
65	271 i
71	306 i
72	245 i
73	506 i
74	174 i
114	712 i
115	152 i
116	754 i
122	225 i
125	365 i
131	364 i
132	546 i
134	223 i
143	412 i
145	274 i
152	115 i
155	731 i
156	265 i
162	503 i
165	251 i
172	036 i
174	074 i
205	263 i
212	356 i
223	134 i
225	122 i
226	411 i
243	351 i
244	025 i
245	072 i
246	523 i
251	165 i
252	462 i
255	446 i
261	732 i
263	205 i
265	156 i
266	454 i
271	065 i
274	145 i
306	071 i
311	664 i
315	423 i
325	526 i
331	465 i
332	455 i
343	532 i
346	612 i
351	243 i
356	212 i
364	131 i
365	125 i
371	734 i
411	226 i
412	143 i
413	054 i
423	315 i
431	723 i
432	516 i
445	043 i
446	255 i
452	053 i
454	266 i
455	332 i
462	252 i
464	026 i
465	331 i
466	662 i
503	162 i
506	073 i
516	432 i
523	246 i
526	325 i
532	343 i
546	132 i
565	703 i
606	631 i
612	346 i
624	632 i
627	031 i
631	606 i
632	624 i
654	743 i
662	466 i
664	311 i
703	565 i
712	114 i
723	431 i
731	155 i
732	261 i
734	371 i
743	654 i
754	116 i

Video about CTCSS and DCS subtones

In this video, you can find out what subtones are, why they are needed and when to use and enter them, and when it is better not to use them.

Tone protection of the radio and the function of scanning subtones allows you to negotiate with great convenience, "filtering" part of the tones from the air. To implement the principle, special CTCSS and DCS codes are used with a frequency in the range of 33-254 Hz. They refer to specific tones that a third-party radio cannot "hear" because they are removed from the audio signal before it reaches amplifiers and equipment systems.

CTCSS Analog Tone Table

DCS Numeric Code Table

How CTCSS and DCS work

The threshold operation of the noise suppressors in the radios can be adjusted - in particular, it can be set so that the device responds only to the least strong required signals. If they are not there, the noise will "close". You can open, block the noise canceling device with subtones that match the value on both sides. If the scan function of the walkie-talkie in TX mode is activated, they will connect to the signals at about 20 percent volume.

The presence of subtones will be determined by the decoder on the receiving side, and the code for blocking the operation of the LF amplifier at the output will open. The desired signal will go to the radio station, and third-party ones will be filtered, and the people who are talking will not hear them. For the circuit to work, it is important to set up uniform subtone values. Otherwise, one of the subscribers will not hear the second.

The convenience of CTCSS and DCS is that interference can be avoided with them - for coded receivers, the noise canceling device does not open and the speakers do not turn on. However, the confidentiality of the conversation is not ensured - it can be heard by people with a walkie-talkie on which the tones decoder is disabled.

The sound amplifier will turn on if both voice and CTCSS / DCS are present in the receive signal. The system works like this:

• if CTCSS is not activated, all signals are heard in the radio;
• if CTCSS is activated, those transmitting the same signal can be heard in the equipment;
• if the desired tone frequency is accidentally present in the noise, when the function is turned on, extraneous signals can break through into the conversation.

When using the function, the noise immunity is slightly reduced, which should be remembered. For high-quality decoding, you need to "clean" signals from interference. One more nuance - if CTCSS / DCS are turned on, the radio station spends 0.1-1 second on their "identification", which slightly slows down the appearance of sound on the receiving radio.

When the function is applied

Subton is used where:

• there are weak, short-term, but interfering with the conversation, interference - without constant activation of the squelch, the “hiss” will not be heard;
• on one of the frequencies there are interfering radio devices, but there are few of them and they are active for a short time - after turning on the function, they will not leave the air, but the receiving and transmitting sides will not hear them and will not be distracted;
• it is necessary to exclude the transmission of interference - in repeater or other automated systems.

Differences between signals

The only difference is the waveform. CTCSS is an analogue tone whose frequency is determined by a grid number. For example, # 18 runs at 123 Hz. DCS also uses low frequencies, but it also contains a digital code.

CTCSS is a sine wave that is downmixed to the desired signals during transmission. DCS is a "rectangle" formed from different digital sets. The sound is also not the same, but the difference is insignificant. CTCSS codes differ in receive tone frequency. Differences in DCS are the sequence of zeros and ones that form it.

You can learn more about the useful functionality of radio stations and choosing the most suitable model from the professional consultants of the MidlandRus online store.

In this article, we will talk about some of the features of portable civilian radios. Namely, we will talk about the CTCSS and DCS subtones. Not all users understand what these tones are and a very large percentage of unknowing people mistakenly assume that by entering a subtone they will be able to encode their channel and protect themselves from extraneous curiosity. So I'll tell you that everything is exactly the opposite. You will not protect yourself from strangers in this way, and even more ... you will limit yourself in receiving information, therefore, by turning on the subtones, you will no longer be able to hear people who operate on the same frequency and who do not have a subtone turned on.

Now let's take a closer look. The subtones are analog CTCSS and digital DCS. How it works? If we enable this function, then the radio station begins to mix a signal of a certain frequency from 67 Hz to 254.1 Hz to our conversation if it is an analog CTCSS subtone, or a certain digital code if we choose a digital DCS subtone. What happens on the back of the radio station in which this function is connected? The radio station constantly monitors the broadcast, and as soon as a signal appears with an admixed subtone, exactly the one that we entered, the radio station electronics begins to give us the transmitted signal into the speaker, having previously cut out the same subtone from the useful signal.

In theory, everything works out very well. It turns out that many channels can be made at one frequency. But in fact, there are many negative points in such situations. Firstly, if you work at some kind of long distance, then you run the risk of greatly reducing the communication range. In a normal situation, you would hear at least some kind of signal, you could make out the speech and understand what they want from you. But by turning on the subtone, the walkie-talkie may not highlight the very code in a weak signal and simply will not open. It turns out that from the fact that you could at least hear something, you really will not hear absolutely nothing. This is the first moment. The second negative point can be illustrated with the following example. The two groups operate on the same frequency, but with different subtones. In one group, a person transmits a signal, walkie-talkies open at this frequency and at the same moment a member of another group begins to go on the air. The radio is already open with us for this frequency, the signals are mixed, so to speak, unexplored phenomena and processes occur, and we again get a zero result.

But there is still one positive point. Imagine a situation where a group of people is working somewhere within a city at a short distance. Those who often use radio stations could not help but notice that very often all sorts of interference breaks into the air. So in such a situation, it makes sense to enable the use of subtones, Thus, we will protect ourselves from extraneous noise.

Almost all radios allow analogue CTCSS tones, and there are quite a few radios with DCS Digital tones. Take a radio station for example , . For little money, they have all the above functionality and allow you to enter 50 analog and 210 digital subtones. You can see the frequencies that correspond to the subtone numbers in this table:

There are also radio stations with a different number of tones, namely 38, 39, 43, 48, 50. You can determine the correspondence of frequencies and subtone numbers in the following table:

And now, at the end of our conversation, I will still express my opinion. As for me, it is better to try to change the frequency to a free one, and if nothing comes of it, then resort to the help of subtones.

What is CTCSS and DCS (CDCSS)

In simple terms: CTCSS and DCS are such "special" sounds mixed with the sounds of the radio operator's voice and transmitted along with him on the air.
CTCSS or DCS sound is not heard on another radio station just because it is simply removed from the audio signal before the audio signal enters the amplifier and then into the radio station's sound system.
CTCSS signals are a tone with a frequency of 33 hertz to 254.1 hertz, depending on the CTCSS number, for example, 18 tones in a 38-tone grid is a tone with a frequency of 123 hertz.
DCS signals are also low frequency signals, but they contain a digital code.

How CTCSS and DCS Works

It's simple - on the transmitting side, a special CTCSS or DCS signal is mixed (mixed) with the signal from the microphone, about 20% of the signal from the microphone, then all this is broadcast by the radio station.
On the receiving side, the sound amplifier is turned on only if a specified CTCSS or DCS is detected in the received signal, in addition to voice.
By turning on CTCSS or DCS, you simply will not hear signals that do not contain CTCSS or DCS, but they will remain on the air.

The CTCSS and DCS trick
Consider the situation when you, your Friend, are Thekaloid.
You communicate with a Friend, and Thekaloid tells you obscene language, interrupting your Friend, and sometimes just taunts you and the Friend.
You and Friend, turn on CTCSS and stop hearing Thekaloid, everything seems to be fine, if not for a couple but:
- You are still on the same channel;
- The fecaloid has not disappeared anywhere from this channel.
What it is fraught with - the Friend wants to inform you that a bear attacked him, Thekaloid turns on simultaneously with your Friend and, mixing with his signal, "clogs" (makes it illegible), as a result, you hear neither Thekaloid nor the Friend.
And that's not all bad.
In order for the radio station, receiving the signal, to be able to determine whether the transmitted signal contains the required CTCSS or DCS, it takes a short time, besides, the signal must be sufficiently clear of interference for the determination (decoding) to be successful.
That is, including CTCSS or DCS, you need to remember that, albeit a little, the noise immunity of communication decreases.

When is CTCSS and DCS appropriate?

1) Where there are a lot of not strong or short-term, but annoying interference.
It's unpleasant when a radio station constantly opens its noise suppressor from interference, and it constantly buzzes for nothing. Enabling DCS or CTCSS will help. Interference does not contain a DCS or CTCSS tone and, accordingly, when it occurs, the radio will not be in vain.
2) Where there are interfering stations on the same frequency, but there are few of them.
If there are few interfering stations, they do not transmit for a long time, and you are ready to accept the fact that you can lose some part of the messages of "your" stations, then it is quite justified to turn on CTCSS or DCS. You will not be distracted by the negotiations of the interfering countries, but you need to remember that the interfering stations have not gone anywhere, you are still on the same channel with them, you just do not hear them now, although they will be able to hear you by turning off CTCSS and DCS.
3) In automatic systems such as repeaters.
In order not to broadcast noise in vain.

304 channels out of 8 - myth or reality?

It is a myth.
It is impossible to make 304 channels out of 8 real channels (frequencies) without using the most complex digital methods (to which neither CTCSS nor DCS apply) by multiplying each channel by 38 CTCSS tones.
If you think of a channel (frequency) as a highway, then CTCSS can be thought of as "just close your eyes". If you close your eyes to some objects and cars on the road, instead of one road your personal "sub-road" will not appear, where there are no other cars and lampposts, you will simply cease to see those already existing on the road, with all the ensuing consequences.

Answers to some popular questions about CTCSS and DCS

If I have not turned on CTCSS, but my friend has turned on, who will hear whom?
You will hear your friend, but your friend will not hear you.
A radio station that does not have CTCSS enabled hears everyone.
A radio station on which CTCSS is enabled hears only those transmitting the same CTCSS.

How does one CTCSS code differ from another?
CTCSS codes differ in the frequency of the tone that is mixed with the wanted signal for transmission and that is expected in the received signal.

How does one DCS differ from another?
They differ in the sequence of 0 and 1 of which the tone signal is generated.

Why sometimes, even with CTCSS or DCS turned on, sometimes some signals break through?
Because, for example, in noise, the desired tone frequencies may be present, which are similar to the CTCSS or DCS that you turned on.

Why is it not immediately audible when CTCSS is on, you press on one radio station to transmit and the sound in another appears only after a few fractions of a second?
The receiving station with CTCSS or DCS enabled takes some time to recognize the CTCSS or DCS in the transmitted signal. Depending on the radio model, this identification may take approximately 0.1 to 1 second.

Is it possible to calculate CTCSS or DCS by receiving a signal from the air?
Yes, you can. And it's very easy.
There are radio stations on the market, and household ones, not expensive ones, which already have a built-in CTCSS or DCS decoder.
If you slightly modify any radio station - take the signal before the filter that removes the low-frequency CTCSS or DCS tone and feed it to the line input of the computer sound card, you can see the mixed CTCSS or DCS tone in the sound editor, and for CTCSS you can immediately measure its frequency.
In addition, from the modified station, you can simply, into a computer, record a signal that contains CTCSS, then "cut off" all frequencies above 300 hertz with filters and get a finished track, overlaying (mixing) with which the desired sound signal and transmitting it to the air, connecting directly to the radio station modulator, immediately open the "closed" CTCSS receiver, with DCS it is a little more difficult, but everything is also very simple.

CTCSS code table (frequencies of CTCSS codes and correspondence of frequencies to CTCSS numbers)

subtone frequency	1 of 38 codes	1 of 39 codes	1 of 43 codes	1 of 48 codes	1 of 50 codes
62.5				1
64.7				2
67.0	1	1	1	3	1
69.3		2	2	4	2
71.9	2	3	3	5	3
74.4	3	4	4	6	4
77.0	4	5	5	7	5
79.7	5	6	6	8	6
82.5	6	7	7		7
85.4	7	8	8	10	8
88.5	8	9	9	11	9
91.5	9	10	10	12	10
94.8	10	11	11	13	11
97.4	11	12	12	14	12
100.0	12	13	13	15	13
103.5	13	14	14	16	14
107.2	14	15	15	17	15
110.9	15	16	16	18	16
114.8	16	17	17	19	17
118.8	17	18	18	20	18
123.0	18	19	19	21	19
127.3	19	20	20	22	20
131.8	20	21	21	23	21
136.5	21	22	22	24	22
141.3	22	23	23	25	23
146.2	23	24	24	26	24
151.4	24	25	25	27	25
156.7	25	26	26	28	26
159.8			27	29	27
162.2	26	27		30	28
165.5			28		29
167.9	27	28		31	30
171.3			29		31
173.8	28	29		32	32
177.3			30		33
179.9	29	30	31	33	34
183.5			32	34	35
186.2	30	31	33	35	36
189.9			34	36	37
192.8	31	32	35	37	38
196.6			36	38	39
199.5				39	40
203.5	32	33	37	40	41
206.5				41	42
210.7	33	34	38	42	43
218.1	34	35	39	43	44
225.7	35	36	40	44	45
229.1				45	46
233.6	36	37	41	46	47
241.8	37	38	42	47	48
250.3	38	39	43	48	49
254.1					50

DCS Codes Table and Their Correspondence to Inverse DCS Codes

Why is this table?
For example, in Yaesu FT-857 there is DCS code 125, however, in Baofeng UV-3R all transmission codes are inverted, with the letter I, respectively, to transmit a code similar to DCS code 125 to Yaesu in Baofeng, you must set the code 365I.

Direct DCS	Inverse DCS
023	047 i
025	244 i
026	464 i
031	627 i
032	051 i
036	172 i
043	445 i
047	023 i
051	032 i
053	452 i
054	413 i
065	271 i
071	306 i
072	245 i
073	506 i
074	174 i
114	712 i
115	152 i
116	754 i
122	225 i
125	365 i
131	364 i
132	546 i
134	223 i
143	412 i
145	274 i
152	115 i
155	731 i
156	265 i
162	503 i
165	251 i
172	036 i
174	074 i
205	263 i
212	356 i
223	134 i
225	122 i
226	411 i
243	351 i
244	025 i
245	072 i
246	523 i
251	165 i
252	462 i
255	446 i
261	732 i
263	205 i
265	156 i
266	454 i
271	065 i
274	145 i
306	071 i
311	664 i
315	423 i
325	526 i
331	465 i
332	455 i
343	532 i
346	612 i
351	243 i
356	212 i
364	131 i
365	125 i
371	734 i
411	226 i
412	143 i
413	054 i
423	315 i
431	723 i
432	516 i
445	043 i
446	255 i
452	053 i
454	266 i
455	332 i
462	252 i
464	026 i
465	331 i
466	662 i
503	162 i
506	073 i
516	432 i
523	246 i
526	325 i
532	343 i
546	132 i
565	703 i
606	631 i
612	346 i
624	632 i
627	031 i
631	606 i
632	624 i
654	743 i
662	466 i
664	311 i
703	565 i
712	114 i
723	431 i
731	155 i
732	261 i
734	371 i
743	654 i
754	116 i