Cellular signal booster selection.

Automatic gain control (AGC) systems are widely used in radio receivers for various purposes. AGC systems are designed to stabilize the signal level at the output of amplifiers of radio receivers with a large dynamic range of input signal changes, reaching, for example, 70-100 dB in radar receivers. With such a change in the input signal level, in the absence of an AGC system, the normal operation of the receiving devices is disrupted, which manifests itself in overloading the last stages of the receiver. In systems of automatic target tracking of a radar, overloading the receiver stages leads to distortion of amplitude modulation, to a decrease in the gain and to a breakdown in tracking. In frequency stabilization systems, cascade overload causes a change in the slope of the discrimination characteristic, which sharply reduces the quality of the system.

According to the principle of constructing AGC systems, they are divided into three main types: open-loop, or without feedback (Fig. 2.2, 2.3); closed, or with feedback (Fig. 2.4); combined. There are single and multi-loop AGC systems with continuous and digital adjustment. AGC without feedback provides a high constancy of the amplitude of the output signal when the input signal changes over a wide range, however, the controlled value depends on the stability of the parameters of the AGC circuit.

An open-loop inertial AGC system (Fig. 2.2) incorporates an adjustable amplifier (U), an AGC system amplifier (UAGC), an AGC detector (DAGC) to obtain a control action and a low-pass filter (LPF) that eliminates the modulation frequency component to avoid demodulation AM radio signal.

Rice. 2.2 - Structural diagram of an open inertial

AGC systems

The time system (Fig. 2.3) contains a control voltage generation device (VARU), whose operation is synchronized in time by an external pulse.

Rice. 2.3 - Structural diagram of the open-loop time AGC system (а)

and a timing diagram explaining the principle of its operation (b)

In practice, the most widely used are inertial AGC systems with feedback (Fig. 2.5). They are divided into systems of continuous and pulse action. All of these systems can be delayed or non-delayed.

Rice. 2.4 - Structural diagrams of continuous AGC systems

with feedback (a) - not amplified with combined detection, (b) - not amplified with separate detection

The principle of operation of the AGC system is as follows. Input voltage U in ( t) is fed to the input of a variable gain amplifier. The output voltage from the amplifier is fed to the input of the detector, then the detected signal is added to the delay voltage U h. Total voltage U c is amplified by a DC amplifier (UPT) and fed to a low-pass filter (LPF), the LPF generates a control voltage U y, which changes the gain. The dependence of the amplifier gain on the control voltage is called the control characteristic, it can be approximated by a linear dependence

, (2.0)

where k 0 is the gain at the control voltage equal to zero;

 is the slope of the control characteristic.

Rice. 2.5 - Functional diagram of the enhanced delayed delay system

AGC with feedback

The effect of stabilizing the output voltage level U out ( t) is achieved due to the fact that with an increase in the level U out ( t) increases and the control voltage U y, under the action of which, in accordance with expression (2.1), the gain of the amplifier decreases, which leads to a decrease in the input signal level.

To prevent a decrease in the output signal level at small input influences and to ensure the operation of the AGC system from a certain level, a delay voltage is applied to the system U h. As a result, the control voltage will appear only when the voltage at the output of the amplitude detector exceeds the delay voltage U h.

, if
, (2.0)

, if
,

where K e is the detector transfer coefficient.

The low-pass filter in the feedback circuit of the AGC systems is designed to transmit the control voltage with the frequencies of the change in the level of the AGC output voltage. In this case, the LPF must be inertial with respect to the frequencies of the useful modulation, otherwise the useful signal will be demodulated.

AGC output voltage

Equations (2.2)–(2.3) correspond to the block diagram of the AGC system (Fig. 2.6). In this scheme, a nonlinear link (NC) is described by the dependence

(2.0)

In the steady state (at a constant voltage level at the input of the AGC system) from (2.2)–(2.4) follow:

at u d< u h;

at u e  u h, (2.0)

where k upt is the amplification factor of the UPT.

Rice. 2.6 - Structural diagram of the AGC system

with feedback

Equation (2.5) defines the control characteristic of the AGC system with feedback.

Rice. 2.7 - Amplitude characteristics of the AGC system

The amplitude characteristics of the closed AGC system (Fig. 2.7.) are presented for the cases: 1 - without the AGC system, 2 - simple AGC, 3 - delayed AGC, 4 - enhanced and delayed AGC.

The cellular communication amplification system is designed to ensure reliable reception of GSM signals for subscribers of MTS, BeeLine, Megafon networks in the Customer's country house.

The reasons for the unstable operation of cellular communications at the facility are:

1. The presence of a dense forest around the village.
2. Thick exterior brick walls of the house.
3. Remoteness from base stations of cellular communication.

To ensure reliable reception of cellular communications in the house, it is necessary to inspect the object for the level of cellular signal in various parts of the house before carrying out construction (repair) work.

It is very important that this survey, and the subsequent design and installation of the system, be carried out by specialists, since for this they have the necessary equipment, skills and experience, as well. also, the knowledge of how much this level will fall in the house after finishing finishing work in the house.

Even if the signal in the house on the 1st and higher floors is more or less tolerable, then on the basement, as a rule, it is completely absent and measures are needed to broadcast the cellular signal to this floor.

It should be borne in mind that finishing work significantly dampens the signal and it is necessary to foresee this moment during the design of the system.

Typically, the system consists of:

An external antenna (external antennas) deployed outside the building in the zone of at least some signal reception from a cellular base station.
- Signal repeater(s), which receives the signal from an external antenna, amplifies it and sends it to the internal antennas installed in the house.
- Internal antennas that communicate with users' cell phones and provide traffic to the cellular base station.

Attention:
1. Repeaters, internal antennas are installed in the house secretly, their installation sites must be serviced. Also, they are connected by high quality cables. Therefore, the system must be carefully designed before finishing work in the house.
2. There is a misconception that cellular amplification systems are harmful to health due to supposedly emitting radio signals that are amplified by this system.

In fact, it is not exactly the opposite.

The fact is that when the level of a cellular signal corresponds to an acceptable level, it has the same effect on a person as on a city street, in a city apartment, office building, etc., and, precisely, does not bring any harm .

If, however, the level of cellular communication is low or completely absent, then your cell phones begin to emit a strong signal to search for a base station (have you noticed how quickly a cell phone is discharged when there is no cellular signal?). Thus, it is the absence of a signal in any area that causes an increased radiation of the radio signal by the telephone. But this does not mean anything, because. So far, the negative impact of cellular radio signals on humans has not been proven.

If you decide to amplify the cellular signal in the country, or in the apartment on your own, then in order to get a positive result, we recommend avoiding the mistakes that people with insufficient experience or knowledge in this field often make. SotSignal specialists have prepared an article for you that will help you minimize the risk of negative consequences when installing and connecting equipment.

1. Error when choosing an amplifier

"Amplifier" refers to the main unit of the system, which is also called a repeater or repeater. It is in the case of this equipment that the key process takes place, providing signal amplification. Also, the system requires appropriate peripheral equipment, namely:

External (donor) antenna;
- internal (service) antenna;
- conductive cable.

In order to correctly select all the elements of the system, it is very important to determine the frequency range of your operator, as well as take into account the area of \u200b\u200bthe room and its configuration.

You will receive a set of numerical values that must be correctly interpreted. In simple terms, a value of -65 ... -75 dB will mean a good signal level in this range. Readings from -95 to 110 dB indicate poor reception up to the complete absence of a signal. The basic idea is this: the worse the signal level, the more powerful amplifier you will need.

But there are many nuances here:

different operators on the same frequency bands can have completely different results. In practice, this is easily detected when one operator is stable and the other is not.
measurement results at different points on the same object, as well as inside and outside the room, can vary significantly.
a good signal on GSM900 or GSM1800 frequencies does not guarantee communication without interference and interruptions in the presence of 3G and 4G LTE frequencies with unsatisfactory readings. The protocols of the radio modules of modern smartphones automatically switch to higher frequencies without analyzing their stability. In this case, when choosing equipment, you will have to “work” with 3G and LTE bands.
the power of the amplifier should be comparable to the number of internal antennas, the length of the cable and the total signal amplification area. The more antennas, the more scattered and weaker the signal will propagate indoors.

The number and type of indoor antennas will depend on the size of the room you need to cover.

Depending on the initial reception conditions, the presence of ceilings and the area of the room, the choice in favor of a particular model of equipment can differ fundamentally! That is why, before preparing a commercial offer, SotSignal specialists always go to the site with special measuring equipment, conduct an inspection and assume the remoteness of the system parts from each other during installation.

2. Incorrect installation of the external antenna

In order for the amplification of the cellular signal in the apartment and in the country house to work as efficiently as possible, it is important to correctly determine the installation location of the external antenna, where the signal from the operator's base station will be the best and most confident, with minimal natural obstacles in its path. When amplifying the signal of two or three operators at once, it is necessary to select a point from which access to several corresponding communication towers is opened at once.

You can diagnose the direction of the signal using your mobile phone: in the place and direction where the signal level on the phone will be the highest and most stable, install and securely fix the external antenna.

Some donor antennas steer comfortably through almost 360 degrees when mounted on a bracket. In the long term, this helps to quickly redirect the antenna when the network configuration changes in the field.

3. Incorrect installation of internal antennas

If you are installing a cellular signal booster system yourself, you need to provide isolation between the internal antennas and the external antenna. Otherwise, the so-called loopback will occur when the external antenna receives a signal from the internal, and not from the base station of the cellular operator. That is, the same signal is repeatedly amplified in a circle and the system stops working.

Do not install antennas in close proximity to each other, in metal and mirror boxes that shield the signal.

4. Using the wrong cable

Choose a high-quality high-frequency cable based on the input impedance of the antennas and amplifier (50 ohms is standard). Thus, you will get the least signal attenuation from the base station.

It should be noted that the shorter the cable length, the lower the potential loss of signal power. If you need to run a long cable run, you will need an additional linear amplifier to ensure optimal system performance.

5. Incorrect connection of system devices

At this stage, you need to carefully check the connection sequence of all devices, as well as the reliability of the connections in order to avoid breakage or failure of the cellular repeater. In addition, an incorrect connection can cause interference and interruptions in communication not only in your premises, but also negatively affect the quality of communication of other users. If the system is installed and connected by you incorrectly, and other subscribers decide to find the culprit, then with the help of special equipment it will not be difficult to do this. After that, the guilty party will incur penalties and compensation for damages.

Amplification means are designed for prompt transmission of speech information, notification of a large crowd of people and signaling.

The sources of speech information can be directly employees, and technical means, such as tape recorders or radios.

Designed to convey information, both to employees of the internal affairs bodies, and to transfer information to citizens, individual offenders, etc.

The block diagram of speech amplification means is shown in fig. 6.1.

Rice. 6.1. Structural diagram of speech amplification means
SU - signaling device; M - tape recorder; Pr - receiver

Any means of amplifying sound consists of a microphone, an amplifier powered by a power source and a loudspeaker. The amplifier may contain a line input to which external sources of speech information are connected, for example, devices for recording or storing speech information (tape recorders, MP3 players, voice recorders, CD players, etc.) or radio receivers.

The microphone converts acoustic vibrations into electrical vibrations proportional to them, i.e. is an acoustoelectric transducer. However, the resulting electrical oscillations are very low-power, small in level and are approximately 1-100 mV. In order to reproduce sound with the required power level, it is necessary to increase the power of weak electrical oscillations and increase the level to 10 V.

This task is performed by a power amplifier, which is an electronic (semiconductor) circuit. Amplifiers use the ability of active elements (transistors, microcircuits) to change some of their parameters and, ultimately, to amplify signals.

An amplifier is an electronic device that increases the power of electrical signals by consuming DC power. source of power. The power source can be a battery (accumulator battery) or a secondary power source that converts the mains voltage (alternating voltage 220 V) into a constant of the required rating.

Amplifier Specifications:

amplified frequency range;

gain;

supply voltage;

power.

The classification of speech amplification means is shown in fig. 6.2.

Rice. 6.2. Classification of speech amplification means

Stationary amplification means are installed in halls, rooms, open spaces and cannot be moved. They are used to ensure daily activities, to inform the relevant units and individual employees of the internal affairs bodies, during formations, meetings, and conferences. Structurally, they consist of permanently installed speakers, microphones, and an amplifier spaced apart in space. There are certain features in the organization of sounding of open spaces and premises.

Sounding the premises is one of the most difficult tasks in practical terms. The sound quality is determined by the volume and intelligibility of speech. Loudness depends on the degree to which the level of the useful sound signal exceeds the level of the existing background noise, speech intelligibility depends on many factors, including the quality of sound reproducing equipment, the acoustic properties of the room, the location of sound reproducing devices, and much more.

Loudness and intelligibility are interconnected due to the following circumstances: the sound field in the room consists of two components - the sound emitted by the sound-reproducing equipment (direct sound) and reflected from the enclosing surfaces (diffuse sound). The ratio of diffuse sound to direct sound is called the acoustic ratio of the room. For normal intelligibility, the acoustic ratio should have some optimal value: at a low acoustic ratio, when the magnitude of the direct sound exceeds the diffuse level, speech becomes abrupt, while at a high one, speech or music becomes unintelligible, turning into cacophony. Thus, for each room there is its own optimal power and layout of sound reproducing devices.

The specifics of open space sounding is that large areas have to be sounded, and the distances between sound sources are significant: if the speaker placement is incorrectly chosen, echo can occur (both in open spaces and in large rooms). Secondly, the propagation of sound waves in open spaces depends on climatic factors and the state of the atmosphere (dustiness, presence of fog, etc.). Thirdly, acoustic interference is always present in open spaces.

Also, when designing sound systems for open spaces, it is important to take into account the level of sound pressure that loudspeakers create at the border of the sounding zone and beyond. If there are residential areas, hospitals, etc. nearby, then the people located there may be disturbed by the sound transmission designed for the main area. Therefore, the level of the sound field outside the sounded zone should not exceed the specified sanitary standards, provided that the rated power is supplied to the sound system.

An example of a stationary amplification system is shown in fig. 6.3.

The GROM public address system is designed to equip premises and open areas where a public address system is required. The system provides speech broadcasting, the possibility of giving sound signals in emergency cases ("Alarm"), feedback. Food is carried out from a network in 220B.

The difference between portable means of speech amplification and stationary ones is that the elements of the system, which may coincide with stationary ones, however, they are not permanently installed, but can be transferred or transported and deployed in a new place.

Rice. 6.3. Public address system "Thunder"

Portable means of amplifying speech are installed on a car base with the help of special mounts. As a rule, such systems are powered by the vehicle's on-board network. Structurally, the loudspeaker amplifier and microphone are separated in space. The loudspeaker is mounted on the car roof with the help of special fasteners. The amplifier is located in the cabin and has an external microphone, combined in one housing with the control unit. The representatives of this group are various signal-loud-speaking devices (SGU).

SGU must be equipped with all special vehicles of the internal affairs bodies. A distinctive feature of the SGU is the presence of light signal beacons, which make it possible to give, in addition to sound (“siren”), light signals. Sound signals are given from a moving car when providing priority passage, chasing another car, escorting convoys of vehicles, etc.

In addition to special sound signals, the SGU allows you to broadcast information through a microphone, for example, various commands and instructions to drivers of moving vehicles and pedestrians. Cars equipped with SGU can also be used when carrying out activities to ensure public order in crowded places, since their output power is an order of magnitude higher than electric megaphones. Using car radios (by connecting them to the SGU) and forming a radio channel, it is possible, for example, from a staff car to simultaneously broadcast the necessary information to several points within a stable radio link. It is also possible to act during operations to capture armed criminals who are in any shelter in order to negotiate with them or divert their attention.

SGU "Ermak" is shown in fig. 6.4.

Rice. 6.4. SSU "Ermak"
a) light-acoustic block; b) LEDs; c) BARS power unit and 4-button microphone with control function

To supply light signals to the Ermak SSU, an LED installation is used: 2 blocks of 16 LEDs. A distinctive feature of the use of LEDs is low power consumption and high brightness of the flash, which is clearly visible from different angles of view due to the special arrangement of the LEDs. The amplification system provides a sound pressure of 120 dB. Sound and light operating modes of the ERMAK SSU are controlled entirely from a four-button microphone. Light indication allows informing the crew of the patrol car about the selected mode. The loudspeaker is structurally placed in the light-acoustic block. This arrangement, in comparison with a similar loudspeaker under the hood, provides more opportunities when working with a microphone and increases the perception of the required information by road users.

Wearable devices are powered by batteries or accumulators, have small dimensions, the amplifier is usually combined with the loudspeaker horn. The microphone is either remote, connected to the amplifier with a short conductor, or located in the same housing with the amplifier. The representative of this group are electromegaphones.

The electric megaphone consists of a microphone insensitive to acoustic interference, an amplifier of low-frequency electrical oscillations and a horn loudspeaker with a handle that allows you to hold it in your hand.

Powerful electric megaphones are equipped with a carrying strap. The microphone (usually located at the end of the electromegaphone) is positioned so that it has the least sensitivity from the side of the loudspeaker (in the direction of sound emission), in order to prevent the occurrence of positive feedback, leading to self-excitation of the amplifier and the publication of a piercing characteristic squeak. With an extension cable, the microphone can be moved away from the loudspeaker for some distance (for example, when the loudspeaker is carried on a shoulder strap or mounted on a car roof). As a rule, electric megaphones have the ability to record both from batteries and from an external power source, such as a car's on-board network. Some provide the ability to give sound signals, such as a "whistle" or "siren".

Electromegaphone EM-15 is shown in fig. 6.5.

Rice. 6.5. Electromegaphone EM-15

Electromegaphone EM-15 is designed to give voice messages and signal "Siren" in open space and in large enclosed spaces. It is used in open space (stadium, square, etc.) at a distance of up to 1000 m in the direction of the wind and with a side wind of up to 5 m / s and in large enclosed spaces. It is a functional analogue of the EM-12 electromegaphone. It is characterized by high speech intelligibility and low power consumption. The duration of continuous operation is at least 10 hours. On the body of the electric megaphone there is a Siren button, as well as sockets for connecting a microphone and an external power source to the electric megaphone. For ease of use, the microphone is made remote, which allows you to use it at a distance of up to 1.5 m from the electric megaphone, or rigidly mount it on the cover.

Sound amplification means by employees of internal affairs bodies are used:

When ensuring public order during public events;

When exercising traffic supervision, ensuring priority passage of special vehicles, promoting traffic rules;

In the event of mass riots;

When detaining armed criminals, the fight against terrorism.

Requirements for voice messages transmitted using speech amplification tools:

Strict observance of the rules of articulation, providing a clear, unhurried pronunciation of each word, in a voice of medium volume;

If it is necessary to repeatedly repeat the bottom and the same text, it is advisable to record it and then reproduce it using sound recording equipment;

Inadmissibility of arbitrary editing of spoken texts. Standard texts should be prepared for specific typical situations.

When addressing a driver who violates the rules of the road, you should clearly state the type and state number of the vehicle he drives, his subsequent actions, etc.

It is necessary to carefully prepare texts that could be used in the arrest of criminals, especially armed ones. Part of the texts should be designed to ensure the safety of citizens who accidentally found themselves in a danger zone, the other part - to stop the actions of criminals. When detaining an armed criminal, it is sometimes necessary to invite relatives or friends to contact him. In such cases, it is advisable to help them in drafting the text of the appeal, while focusing on the prepared options. Even more options should be prepared to protect public order during mass events.

When using speech amplification tools, it is necessary to take into account weather conditions (wind, rain, snowfall, fog), which affect the quality and range of sound propagation. For best sound amplification performance on a ground vehicle, the horn loudspeaker should be mounted on a turntable, as the vehicle itself cannot always be oriented so that the longitudinal axis of the loudspeaker coincides with the desired direction of sound propagation. It should also be remembered that the higher the loudspeaker is installed, the farther and more clearly the broadcast information will be heard.

The presented calculation of the cellular communication amplification system will confirm the correctness of the selection of equipment and the installation of cellular signal amplifiers.

For example, let's take the simplest case of a mobile voice amplification system.

Initial data

First we need to define the initial data:

The frequency range in which we receive the signal
The signal strength at the location where the external antenna will be or already installed. To measure the signal level, we need a simple phone, namely the Netmonitor service function.

Phone service functions

You can read about what code you need to dial on your phone model in the article “Phone service functions”.

For Android smartphones, it's even easier. For them, there are many free applications to find out the input signal level of the received station, as well as a sea of other useful information, such as network code (MNC), Base Station Number (BSIC), cell ID and much more.

We got a smartphone Samsung GT-S5250.

	We dial the code * # 9999 * 0 # and immediately get into the phone menu service.
	Press "Back" several times in a row until the phone returns to the main menu.
	Select the first item "Debug Screen", enter "1" on the virtual keyboard that appears.
	Next, also enter "1", thereby selecting "Basic Mode Information".

And we get all the necessary information and even superfluous. This phone has a Megafon SIM card installed.

RPLMN: 250-02
250 - country code (250 - Russia, 255 - Ukraine, 257 - Belarus);
02 - network code (01 - MTS, 02 - Megafon, 99 - Beeline, 20 - Tele2);
GSM 900- the mobile communication standard in which the phone is currently working;
BSIC: 19- code of the BS from which the signal is currently being received;
BcchFrq: 102- the number of the channel of the Base Station on which communication is currently carried out, for more information about the channels and their distribution by operators, see the article “The principle of operation of cellular communications”. Indeed, channel 102 in St. Petersburg is used by MegaFon and it is in the GSM 900 range;
RSSI: -63- received signal level in dBm;
RxLev: 47- the level of the signal itself, but in other conventional units, the larger its value, the better the signal.

And so, let's assume that the signal level was measured at the installation site of the external antenna, and it is necessary to amplify the signal in a small basement with an area of 40 m². We will carry out the calculation for the DownLink direction (the signal from the base station to the mobile phone).

Selected equipment

AL-900-11 external antenna, directional, "wave channel" type, gain Ku=11 dB	PicoCell 900 SXB repeater with 60 dB gain and output power up to P=10 mW	AP-800/2700-7/9 ID internal panel antenna with 900 MHz gain - Ku=60 dB	with a short length of strong attenuation of the signal, it will not introduce

The scheme of the mobile communication amplification system will be as follows:

The calculation method is as follows:

We measured the signal level with the phone at the pre-installation point of the external antenna: -63 dBm. The antenna gain is 11 dB, respectively, at the antenna output we have a signal of -63 + 11 = -52 dBm.
Every cable has its own RF characteristics. For example, our 5D-FB cable loses 19.7 dB at 100 meters at 900 MHz (see specifications). The higher the frequency of the signal, the greater the loss in the cable. Accordingly, about 2 dB will be lost at 10 meters. Thus, a signal -52 -2 = -54 dB comes to the input of the repeater.
We look at the gain of the repeater in its technical characteristics (in our case, 900SXB has Ku = 60 dB). We get at the output of the amplifier: -54 +60 = +6 dBm.
In the cable from the repeater to the internal antenna, the loss will be approximately 1dB over a length of 5 meters.
Thus, a signal +6 -1 = +5 dBm comes to the input of the internal antenna.
Antenna gain AP-800/2700-7/9 ID at a frequency of 900 MHz Ku=7 dB. Thus, the antenna will radiate a signal with a level of +5 +7= + 12 dBm.

In order to convert the signal level from dBm to mW, we use the formula: P[mW] =10^(0.1* P[dBm]). In our case: P[mW] =10^(0.1*12)=15.8 mW.

In order to estimate the coverage area and not to carry out complex mathematical calculations of signal attenuation in space, on the basis of experimental data it was found that if the signal level in mW is multiplied by a factor of 4 for the 900 MHz band (for the 1800 MHz band - by a factor of 3), then you can get the approximate coverage area in m². In the presence of walls and partitions, the area may be significantly smaller.