A method of access control in radio communication systems based on the presence in the wanted signal of audio tones of a certain frequency that lie outside the modulation frequency range outside the audible range at frequencies below 300 Hz. The radio station's receiver is activated only when the specified CTCSS tone appears, for which it is programmed. It is a standard feature in most modern radio equipment. More modern method access control -.

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.
When transmitting, a subtone signal is sent (below 300 Hz) a certain frequency(determined by the CTCSS code), which, upon reception, is instantly recognized by the CTCSS squelch as "friend" or "alien". If the code is "own", 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.

In other words, when you receive a signal from a subscriber whose code is different from the one set on your radio station, you do not hear this subscriber. Moreover, the signals you transmit will be heard only by the subscriber whose radio station tone code matches your code.

CTCSS is also used for more effective suppression of interference in the 40 MHz range (Low Band).

Note: Motorola refers to CTCSS as "Private Line (PL)" and GE / Ericsson as "Channel Guard (CG)".

64 Tone CTCSS Code Table

№	Frequency Hz)	№	Frequency Hz)	№	Frequency Hz)	№	Frequency Hz)
1	33.0	17	71.9	33	123.0	49	183.5
2	35.4	18	74.4	34	127.3	50	186.2
3	36.6	19	77.0	35	131.8	51	189.9
4	37.9	20	79.7	36	136.5	52	192.8
5	39.6	21	82.5	37	141.3	53	196.6
6	44.4	22	85.4	38	146.2	54	199.5
7	47.5	23	88.5	39	151.4	55	203.5
8	49.2	24	91.5	40	156.7	56	206.5
9	51.2	25	94.8	41	159.8	57	210.7
10	53.0	26	97.4	42	162.2	58	218.1
11	54.9	27	100.0	43	165.5	59	225.7
12	56.8	28	103.5	44	167.9	60	229.1
13	58.8	29	107.2	45	171.3	61	233.6
14	63.0	30	110.9	46	173.8	62	241.8
15	67.0	31	114.8	47	177.3	63	250.3
16	69.4	32	118.8	48	179.9	64	254.1

Code table 39 CTCSS tones

№	Frequency Hz)	№	Frequency Hz)	№	Frequency Hz)	№	Frequency Hz)
1	67.0	11	94.8	21	131.8	31	186.2
2	69.3	12	97.4	22	136.5	32	192.8
3	71.9	13	100.0	23	141.3	33	203.5
4	74.4	14	103.5	24	146.2	34	210.7
5	77.0	15	107.2	25	151.4	35	218.1
6	79.7	16	110.9	26	156.7	36	225.7
7	82.5	17	114.8	27	162.2	37	233.6
8	85.4	18	118.8	28	167.9	38	241.8
9	88.5	19	123.0	29	173.8	39	250.3
10	91.5	20	127.3	30	179.9

38 CTCSS tone code table

№	Frequency Hz)	№	Frequency Hz)	№	Frequency Hz)	№	Frequency Hz)
1	67.0	11	97.4	21	136.5	31	192.8
2	71.9	12	100.0	22	141.3	32	203.5
3	74.4	13	103.5	23	146.2	33	210.7
4	77.0	14	107.2	24	151.4	34	218.1
5	79.7	15	110.9	25	156.7	35	225.7
6	82.5	16	114.8	26	162.2	36	233.6
7	85.4	17	118.8	27	167.9	37	241.8
8	88.5	18	123.0	28	173.8	38	250.3
9	91.5	19	127.3	29	179.9
10	94.8	20	131.8	30	186.2

Related articles.

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. Thus, you will not protect yourself from strangers, 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 select a digital subtone DCS. What happens on the back side 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 a 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 radio 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 for 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 when a group of people works somewhere within the city for short distance... Those who use radio stations often 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 of 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.

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

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.

When transmitting, a subtone signal (below 300 Hz) of a certain frequency (determined by the CTCSS code) is sent, which, when received, is instantly recognized by the CTCSS squelch as "friend" or "alien". If the code is "own", 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 boss 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), 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 frequency 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.

This device is used to determine the transmission frequency of the portable radio station. Unlike other inexpensive Chinese models, the seller promises that this device also allows you to define CTCSS frequencies and DCS codes. To be honest, when ordering this device, I strongly doubted that the function of determining the codes would work. However ... Details under the cut.

From time to time, I have to participate in all sorts of public events and festivals, sometimes as one of the organizers, sometimes as a volunteer.
At such events, to coordinate the organizational staff, portable radio stations are almost always used, with a range of 70 cm (on LPD frequencies). Orgs usually have a couple of dozen radio stations of the same type at their disposal. Some of them have already died, some are still charging, and the rest were taken away by the people, and you are preparing an important event and need prompt communication ... To avoid all this, I usually take my personal old Yaesu VX2-R.
But often, org's walkie-talkies without a screen, with a channel switch, and what frequencies and security codes are there, only Vasya knows, who has not arrived today, and you cannot get through, since he is generally in Cambodia, and he has long forgotten all these frequencies and codes. Previously, you had to scan the range for a long and dreary time, then select the CTCSS code (of which there are half a hundred), or even the DCS code, of which there are even more.
To avoid all this completely unnecessary fuss, this frequency counter was purchased. I chose this particular model for two criteria - it is inexpensive and it claims the function of determining the CTCSS and DCS codes.

The device arrived from China in 2 weeks, it was packed in a standard yellow bag, heels of layers of pimples, a cardboard box, in which for some reason there was a half of the case from an ancient Motorola portable (Bonus from a Chinese? But very strange), and this piece of plastic is in size almost twice the frequency meter, and weighed almost the same.
The frequency meter itself was packed in a virgin white cardboard box (I didn't take a picture, but take my word for it - it is absolutely white, and completely cardboard). There was nothing in the kit, not even instructions.

The device itself is small, 95x55x23mm, on top of a 7mm pimp of a very modest antenna sticks out, in the unfolded state a little more than 7 cm.

The power button is located at the end, it also serves for all other functions.

The screen is a green LED-synthesizing LED indicator, two lines of 8 characters each. It can be seen perfectly in bright light, worse in dusk. There is no backlight.
To turn on, you need to press the button for about 1 second.
The device will say AUTO 1k, after which it will show 000.000, unless of course there is no signal source nearby. It turns off by itself if you do not press the button for a minute (regardless of which mode it is currently in). You can also forcibly turn off by holding the button for 2 seconds.
When turned on, holding down the button, you can select the frequency determination accuracy - 1 kHz, or 0.1 kHz. To be honest, for me the 0.1 kHz mode is useless, because firstly, the channel pitch is precisely known (it is 25 or 12.5 kHz) and such accuracy is simply excessive, and secondly, in 0.1 kHz mode, frequency capture is required ~ 3 seconds versus 1 s. in 1kHz mode. In addition, the error of the frequency meter itself is unknown.

Further, I carried out all measurements in the 1 kHz mode.
To begin with, I took the key fob from the car alarm and held it to the antenna. The numbers ran on the screen, and when approaching the antenna, segments of the signal level appeared on the bottom line. The device responds in the same way to cellular telephone, Wi-Fi hotspot, microwave included. The device smells the microwave from about 50 cm, the Wi-Fi access point - from 20.

A bit of theory

A little explanation - all these radio transmitters operate in a pulsed mode and the numbers shown by the device have only one relation to reality - they are less than the frequency of the transmitters. This is completely normal and any frequency counter will behave this way. The reason is in the principle of work. Without going into the jungle, the frequency meter simply counts the number of oscillations of the electromagnetic field over a certain period of time (in this case, it seems to me, about a tenth of a second). Both the microwave magnetron and the key fob and wifi transmitters have time to turn off and on many times during this time, respectively, the number of counted oscillations will be less than if the transmitter worked continuously.

If we have a constant frequency source, then the frequency counter behaves differently. If the frequency does not change within a second, it fixes it, and then tries to determine the CTCSS code (another second), and then DCS (somewhere 1-3 seconds).
Then it displays an inscription with the measurement result. In this mode, it no longer responds to signals until you press the button. Then he will say "Reset" and return to the screen with numbers. If you do not press anything, it will simply turn off after a while.

So, let's check the range first. I used my VX2R, which outputs about 1 W at 433 MHz, and 1.5 W at 145. In the room, the frequency is stable at 433 MHz from somewhere from 4 meters, at 145 - from about 1.5-2 ... For such power, it is quite enough, as it seems to me.

Next, I decided to check the declared function of determining CTCSS codes. I set up the portable, press the PTT, a couple of seconds ... It works!

I reset the frequency counter, press it again - and again it is correct.
I was not lazy, I went through all 50 CTCSS codes - all are determined correctly, except for two: the first 67 for some reason was always defined as 69.3, and the last 254.1 - sometimes as 250.3. All other frequencies were almost always determined correctly, out of about a hundred measurements - the device was mistaken twice showing the adjacent frequency, which seems to me to be quite acceptable in this case.
DCS is the same. Unless the definition takes a couple of seconds longer. I did not check all the DCS codes (there are more than a hundred of them), however, two dozen randomly selected ones were identified correctly. (In addition, DCS is digital, with check codes, a situation similar to errors in CTCSS is unlikely).

Well, one more check. The frequency range is stated to be 50-2400 MHz. I took out a car sibishka from the mezzanine, stuck a piece of wire instead of the antenna ... It's funny, but the frequency counter works and determines the frequency correctly. True, the frequency is not captured, the CTCSS, DCS codes are not determined. And once every few seconds, for a split second, the indicator shows strange numbers, but in general it works the same.

There will be no dismemberment. Behind there are 4 screws, under which the battery is located and the board is visible. But in order to get to the most interesting thing, you need to unsolder the antenna, which I'm not ready for yet. However, there is access to a fine trimmer, calibration is possible.

Conclusions.
The device has exceeded expectations, and, in general, fulfills all the declared functions. And in general - I like it. I will not describe the pros and cons, I think that if you need such a device, it is quite possible to take it.
The device was bought for my own money, and at a rate of more than 60 rubles per dollar W (

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 sound signal goes to the amplifier and then to sound system radio stations.
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 audio 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 there is you, your Friend, and there is a Fekaloid.
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 is it fraught with - a 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 do not hear either Thekaloid or Friend.
And that's not all bad.
In order for the radio station, receiving the signal, to be able to determine whether the required CTCSS or DCS is in the transmitted signal, 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 slightly, the noise immunity of communication decreases.

When is it appropriate to use CTCSS and DCS

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 work 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 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 can hear you by turning off CTCSS and DCS.
3) B automatic systems, for example, repeaters.
In order not to broadcast noise in vain.

304 channels out of 8 - myth or reality?

It is a myth.
From 8 real channels (frequencies) without using the most complex digital methods (to which neither CTCSS nor DCS apply), it is impossible to make 304 channels 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 simply will no longer see existing ones 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 a 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 radio 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 tone of CTCSS or DCS and feed it to the line input sound card computer, in the sound editor you can see the mixed tone of CTCSS or DCS, and for CTCSS you can immediately measure its frequency.
In addition, from a 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 code 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