All about CTCSS and DCS subtones. What are CTCSS and DCS (CDCSS) codes, when is it appropriate to use them, why is it not always heard? Bf 728 ctcss dcs range

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

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 your group’s communication, close the channel to a subtone, setting all radios in the group to the same subtone for reception and transmission. There is a short instruction for BAOFENNG, you will need menu items from 10 to 13. We put the same subtones everywhere CTCSS or DCS and you're done!

What is it for?
There are never ideal communication conditions, especially in big cities where, in addition to you, a large number of groups of correspondents can communicate on the same frequencies. And in order for them not to interfere with each other, using the above-mentioned subtones, you can create your own groups that will only hear the signals of radio stations included in it, and the squelch station will ignore radio stations operating on the same frequency, but not included in this group.

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

By setting 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 at a time when the frequency is free.

Modern stations typically use two coding systems:
- CTCSS system(Continuous Tone-Coded Squelch System) is a noise reduction system coded with a continuous low-frequency signal that is mixed into the speech signal, using frequencies below its range from 67 to 257 Hz. Those. you won't even hear them over your station's speakers.

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 to another station, but this is not Baofeng

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

Below is a table of DCS tones and their correspondences

Video about CTCSS and DCS subtones

In this video you can learn what subtones are, why they are needed and when they should be used and introduced, and when it is better not to use them.

The radio's tone protection and subtone scanning function allow you to negotiate with greater convenience, “filtering out” some of the tonal signals 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 are not “heard” by a third-party radio because they are eliminated from the audio signal before it reaches amplifiers and equipment systems.

CTCSS analog tone table

DCS Digital Code Table

How CTCSS and DCS work

The threshold response of noise suppressors in walkie-talkies can be adjusted - in particular, it can be set so that the device responds only to the least strong desired signals. If they are not there, the noises will be “closed”. You can open and block the noise reduction device with subtones that match in value on both sides. If the radio's scan function in TX mode is activated, they will connect to signals at approximately 20 percent capacity.

The presence of subtones will be detected by the decoder on the receiving side, and a code will open to block the operation of the low-frequency amplifier at the output. The required signal will arrive at the radio station, but outsiders will be filtered out, and those talking will not hear them. For the “chain” to work, it is important to set up uniform subtonal values. Otherwise, one of the subscribers will not hear the second one.

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

The sound amplifier will turn on if both voice and CTCSS/DCS are present in the reception 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 are heard in the equipment;
• If the desired tone frequency is accidentally present in the noise, extraneous signals may break into the conversation when the function is turned on.

When using the function, noise immunity is slightly reduced, which should be kept in mind. For high-quality decoding, you need to “clean” the signals from interference. Another nuance - if CTCSS/DCS are turned on, the radio station spends 0.1-1 second to “identify” them, which slightly slows down the appearance of sound on the receiving radio.

When to apply the function

Subtones are used where:

• there are weak, short-term, but interfering with the conversation - without constant activation of the noise suppressor, “hissing” will not be heard;
• there are interfering radio devices on one of the frequencies, but there are few of them and they are active for a short time - after turning on the function they will not go off 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 repeaters or other automated systems.

Differences between signals

The only difference is the signal shape. CTCSS is an analog tone whose frequency is determined by a grid number. For example, No. 18 operates at 123 Hz. DCS also uses low frequencies, but it also contains a digital code.

CTCSS is a sine wave that is mixed to the required 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 the frequency of the tone per reception. The difference in DCS is 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 professional consultants of the MidlandRus online store.

This device is used to determine the transmission frequency of a portable radio station. Unlike other inexpensive Chinese models, the seller promises that this device also allows you to determine CTCSS frequencies and DCS codes. To be honest, when ordering this device, I seriously doubted that the code detection function 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, portable radio stations of the 70 cm range (at LPD frequencies) are almost always used to coordinate the organizational staff. Usually, organizations 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 have been stolen by people, and you are preparing an important event and need operational communication... To avoid all this, I usually take my personal old Yaesu VX2-R.
But often, organizational radios have no screen, with a channel switch, and only Vasya knows what frequencies and codes are hardwired in, but he didn’t come today, but it’s impossible to get through, since he’s actually in Cambodia, and he forgot all these frequencies and codes a long time ago. Previously, you had to scan the range for a long time and tediously, 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 meter was purchased. I chose this particular model based on two criteria - it is inexpensive and it has the function of detecting CTCSS and DCS codes.

The device arrived from China in 2 weeks, was packaged in a standard yellow bag, five layers of bubble wrap, a cardboard box, in which for some reason lay half the case from an ancient Motorola laptop (Bonus from the Chinese? But very strange), and this piece of plastic was the size almost twice the size of the frequency meter, and weighed almost the same.
The frequency meter itself was packed in a pristine white cardboard box (I didn’t take a photo, but take my word for it - it’s absolutely white, and completely cardboard). There was nothing included in the kit, not even instructions.


The device itself is small, 95x55x23mm, with a very modest antenna sticking out at 7mm on top, a little more than 7cm when unfolded.


At the end there is a power button, which also serves for all other functions.


The screen is a green character-synthesizing LCD indicator, two lines of 8 characters each. In bright light you can see perfectly, in the dark - worse. There is no backlight.
To turn it 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 a signal source nearby. It turns off by itself if you don’t press the button for a minute (regardless of what mode it is currently in). You can also forcefully turn it off by holding the button for 2 seconds.
When turned on, by holding the button you can select the accuracy of frequency determination - 1 kHz, or 0.1 kHz. Honestly, 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 the 0.1 kHz mode it is required to capture the frequency ~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 1 kHz mode.
To begin with, I took the car alarm key fob and brought it to the antenna. Numbers flashed on the screen, and when approaching the antenna, signal level segments appeared on the bottom line. The device responds in a similar way to cellular telephone, Wi-Fi access point, included microwave. The device senses a microwave from about 50 cm, a Wi-Fi access point from 20.

A little theory

A small explanation - all these radio transmitters operate in pulse mode and the numbers that the device shows have only one relation to reality - they are less than the operating frequency of the transmitters. This is completely normal and any frequency meter will behave this way. The reason is the principle of operation. Without going into too much detail, 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 magnetron of the microwave and the key fob and Wi-Fi transmitters manage to turn off and on many times during this time; accordingly, the number of counted oscillations will be less than if the transmitter were working continuously.

If we have a source of constant frequency, then the frequency meter behaves differently. If the frequency does not change within a second, it fixes it, after which it tries to determine the CTCSS code (another second), and then DCS (about 1-3 seconds).
Then it displays a message with the measurement result. In this mode, it no longer responds to signals until you press a button. Then he will say “Reset” and return to the screen with numbers. If you don’t press anything, it will simply turn off after a while.

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

Next, I decided to check the claimed function for determining CTCSS codes. I set up the laptop, press the PTT button, a couple of seconds... It works!


I reset the frequency meter, press it again - and again it’s correct.
I wasn’t too lazy, I went through all 50 CTCSS codes - all are determined correctly, except for two: for some reason the first 67 was always determined as 69.3, and the last 254.1 was sometimes determined as 250.3. All other frequencies were determined almost always correctly, out of about a hundred measurements - twice the device made a mistake by showing the neighboring frequency, which seems quite acceptable to me in this case.
With DCS everything is similar. Except that the definition takes a couple of seconds longer. I didn’t check all the DCS codes (there are more than a hundred of them), but two dozen randomly selected ones were identified correctly. (In addition, the DCS system is digital, with control 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 the car radio from the mezzanine and stuck a piece of wire in place of the antenna... It’s funny, but the frequency meter works and determines the frequency correctly. True, the frequency is not captured, CTCSS and DCS codes are not detected. And once every few seconds, for a split second, the indicator shows strange numbers, but overall it works.

There will be no dismemberment. There are 4 screws on the back, under which there is a battery and the board is visible. But to get to the most interesting part, you need to unsolder the antenna, which I’m not ready for yet. However, there is access to a small trimmer and calibration is possible.

Conclusions.
The device exceeded expectations and, in general, performs all the stated functions. And in general, I like it. I won’t describe the pros and cons, I think that if you need such a device, it’s quite possible to buy it.
The device was purchased with my own money, and at an exchange rate of more than 60 rubles per dollar (

An access control method in radio communication systems based on the presence in the useful 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's receiver will only activate when the specified CTCSS tone it is programmed for appears. It is a standard feature on most modern radio equipment. A more modern access control method is .

The tone coding function is necessary to divide correspondents (users) into groups working on the same radio channel. Only those correspondents who have the same CTCSS code (tone) can listen and transmit within “their” group. For those who are not configured for 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) certain frequency(determined by the CTCSS code), which upon reception is instantly recognized by the CTCSS squelch as “friend” or “foreign”. If the code is “own”, then the radio station turns on for reception and plays the message, if it is “foreign”, 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, you do not hear this subscriber. Moreover, the signals you transmit will be heard only by the subscriber whose radio station tone code matches yours.

CTCSS is also used to more effectively suppress interference in the 40 MHz Low Band.

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

64 CTCSS Tone Code Table

Code table for 39 CTCSS tones

Code table 38 CTCSS tones

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