If you decide to strengthen the cellular signal at your dacha or in your apartment on your own, then to get a positive result, we recommend avoiding mistakes that are often made by people with insufficient experience or knowledge in this area. SotSignal specialists have prepared an article for you that will help you minimize your risk negative consequences when installing and connecting equipment.

1. Error when choosing an amplifier

The “amplifier” refers to the main unit of the system, which is also called a repeater or repeater. It is in the housing of this equipment that a key process occurs that ensures signal amplification. Also, for the system to operate, appropriate peripheral equipment is required, namely:

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

To correctly select all 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 ​​​​the room and its configuration.

You will receive a set of numerical values ​​that must be interpreted correctly. 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 no signal at all. The basic idea is this: the worse the signal level, the more powerful amplifier you will need.

But there are many nuances here:

• at different operators for the same frequency ranges there can be completely different results. In practice, this is easily detected when one operator works stably, but the other does not.
• Measurement results at different points on the same object, as well as indoors and outdoors, can vary significantly.
• a good signal on the GSM900 or GSM1800 frequencies does not guarantee communication without interference and interruptions in the presence of 3G and 4G LTE frequencies with unsatisfactory readings. Radio protocols modern smartphones automatically switch to higher order 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 must be comparable to the number of internal antennas, the length of the cable and the total area of ​​the signal amplification. The more antennas, the more diffuse and weak signal will spread indoors.

The number and type of internal antennas will depend on the area of ​​the room you need to cover with communications.

Depending on the initial reception conditions, the presence of ceilings and the area of ​​the room, the choice in favor of a certain equipment model can differ fundamentally! That is why, before drawing up a commercial proposal, SotSignal specialists always visit the site with special measuring equipment, conduct an inspection and assume that the parts of the system are located at a distance from each other during installation.

2. Incorrect installation of external antenna

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

Some donor antennas can be conveniently directed almost 360 degrees when mounted on a bracket. In the future, this helps to quickly redirect the antenna when the network configuration changes in the area.

3. Incorrect installation of internal antennas

At self-installation amplification systems cellular signal you need to provide isolation between the internal antennas and the external antenna. Otherwise, a so-called loopback will occur, when the external antenna takes the signal from the internal one, and not from the base station mobile operator. That is, the same signal is amplified many times in a circle and the system stops working.

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

4. Using the wrong cable

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

Please note that the shorter the cable length, the lower the potential signal power loss. If long cable runs are required, 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 breakdown or failure of the repeater cellular communications. Besides, incorrect connection may 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 using special equipment it will not be difficult to do this. After which the guilty party will incur penalties and compensation for damages.

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

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

Initial data

First we need to determine the initial data:

1. Frequency range in which we receive the signal
2. The signal level in the place where the external antenna will be or has already been 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 “Service functions of phones”.

It's even easier for Android smartphones. There are many for them free applications in order to find out the input signal level of the received station, as well as other useful information, such as Network Code (MNC), Base Station Number (BSIC), Cell ID and more.

We have got it at our disposal samsung smartphone GT-S5250.

	We dial the code *#9999*0# and immediately get to 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, we also enter “1”, thereby selecting “Basic Mode Information”.

And we get all the necessary information and even unnecessary information. IN this phone A Megafon SIM card was 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- standard mobile communications, in which the phone is currently working;
• BSIC: 19- code of the BS from which this moment a signal is received;
• BcchFrq: 102- the number of the Base Station channel on which communication is currently taking place; for more information about the channels and their distribution by operator, read the article “The principle of operation of cellular communications”. Indeed, channel 102 in St. Petersburg is used by Megafon and is in the GSM 900 band;
• RSSI: -63- received signal level in dBm;
• RxLev: 47- the level of the same signal, but in other conventional units, the higher its value, the better the signal.

So let’s assume that the signal level was measured at the location where the external antenna was installed, and the signal needs to be amplified in a small basement room with an area of ​​40 m². We will carry out the calculation for the DownLink direction (signal from the base station to the mobile phone).

Selected equipment

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

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

The calculation method is as follows:

1. We measured the signal level with the phone at the point where the external antenna was pre-installed: -63 dBm. The antenna gain is 11 dB, respectively, at the antenna output we have a signal of -63 + 11 = -52 dBm.
2. Every cable has its own RF characteristics. For example, for our 5D-FB cable, 19.7 dB is lost at 100 meters at 900 MHz (see technical specifications). The higher the signal frequency, the greater the cable loss. Accordingly, at 10 meters about 2 dB will be lost. Thus, a signal of -52 -2 = -54 dB arrives at the repeater input.
3. We look at the repeater gain in its technical specifications(in our case, the 900SXB has Ku = 60 dB). We get at the amplifier output: -54 +60 = +6 dBm.
4. In a cable from the repeater to the internal antenna over a length of 5 meters, the loss will be approximately 1 dB.
   Thus, the signal +6 -1 = +5 dBm arrives at the input of the internal antenna.
5. The gain of the AP-800/2700-7/9 ID antenna at a frequency of 900 MHz is Ku=7 dB. Thus, the antenna will emit 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 carry out complex mathematical calculations of signal attenuation in space, based on experimental data it has been established that if the signal level in mW is multiplied by a factor of 4 for the 900 MHz range (for the 1800 MHz range - by a factor of 3), then it is possible obtain the approximate coverage area in m². If there are walls and partitions, the area may be significantly smaller.

Is it necessary to purchase an expensive gadget when you can get by with a device assembled from improvised materials?

Those who have at least First level knowledge in the field of cellular communications will be able to cope on their own. To do this, you need components and tools, as well as a diagram of the device.

And you can collect simple amplifier cellular communications on your own. What is required for this will be discussed below.

Antennas for amplifying cellular communications

They are among the most simple devices, allowing you to achieve a high-quality signal at any object.

There are two main groups of antennas:

1. External;
2. Internal.

The former are usually installed on the roof of a building and are capable of providing coverage over large areas. The antenna transmits the signal received from the base station through a cable to the amplifier. This guarantees good communication quality even in areas where it was previously impossible.

What elements does the signal amplification system consist of?

It is possible to ensure reliable communication in places that are difficult to reach for a radio signal, but this will require special equipment. Collected in unified system various devices allow you to achieve High Quality signal and forget forever about its sudden disappearance. It is often called a cellular booster. However, in reality it is a complex consisting of the following elements:

• A repeater or two-way amplifier, which is an intermediate link;
• External and internal antennas that pick up the station signal and distribute it indoors;
• Power divider or wire splitter;
• N-connectors;
• Coaxial cable with a resistance of 50 Ohms.

All devices included in the system are divided into two groups:

1. Active;
2. Passive.

The first includes devices that require a connection to a power source to operate - this is a repeater, connectors. Antennas, divider and cable are called passive. Each system is designed for a specific object and therefore may have a different number of amplifiers and internal antennas. The best option is considered to be one that uses a cable of minimal length, since every extra meter is a loss in signal quality. This must be taken into account when assembling a cellular signal amplifier with your own hands.

Since all the elements are interconnected, it is recommended to install the equipment before finishing, so as not to spoil the interior.

Repeater operating principle

Equipment of this class is in some way a repeater. It processes received signals and sends them to the base station tower if it is an outgoing call. When a subscriber is dialed, the repeater performs the same function, only the connection is made with the user’s gadget.

Let's watch the video, the simplest way boost the signal:

Signal reception and transmission is carried out by antennas. The simplest signal amplifier cellular network can be assembled with your own hands. The outdoor antenna receives or sends it to the station, and the indoor antenna is responsible for expanding the coverage area indoors.

How to make a cellular booster with your own hands

Using such a device allows you to achieve high-quality communication in almost any corner of the facility. A repeater is especially necessary in areas with poor signal or where there is no signal. The advantages of using the system include the following:

1. Strengthening the signal in places where there are frequent interruptions in mobile communications;
2. Removing interference;
3. Increased message clarity;
4. Reduced radiation levels;
5. Longer phone battery life.

But since such equipment is not cheap, many decide to make it themselves.

Let's watch the video, the stages of making it yourself:

In order to assemble a cellular communication amplifier on your own, you will need components that need to be connected into a single system. How to do this will be discussed further.

What is needed for assembly

If you decide to make the simplest device, namely an antenna, then you will need:

• Wire, but not copper (length 30-40 cm);
• Connection block;
• Cable (up to 10 m);
• Fasteners (for mounting connecting blocks);
• Polymer pipe (20 cm);
• Plastic.

Since during the work you will have to connect individual elements, it is worth having electrical tape on hand. After all the components have been found and prepared, you can begin assembling the cellular signal amplifier with your own hands.

A piece of wire must be bent in the middle by 90°, so that the end result is a rhombus. To do this, retreat 9 cm from the center in both directions. Then, at the mark, the wire is again bent to the same angle. As a result of the manipulations performed, you get a rhombus. The ends are bent inward and a block is connected to them. Install it so that future connections can be made through it. To do this, cut along one side of the polymer pipe and make a hole on the opposite side.

Watch the video and make an amplifier from cans:

After the antenna assembly stage has been completed, we begin to connect the coaxial cable. At one of its ends, the outer insulation is removed and the outer and inner conductors are connected to the contacts of the connecting block. As a result, the cable becomes an extension of the antenna.

After this, all that remains is to install the device on the roof of the house or attach it to a pole and point it towards the base station of the cellular operator. The last step in making a simple amplifier with my own hands is to connect the other end of the cable to a plastic plate. And you can start testing.

If everything was done correctly, then as soon as you bring mobile phone to the amplifier, the signal indicator will increase by 2 or 3 divisions.

Selecting a repeater installation location

But it’s not enough just to assemble a cellular communication amplifier, you also need to install it correctly. The efficiency of such equipment is directly dependent on its location, as well as the antennas included in the system. Therefore, before proceeding with installation, you must make sure that the signal level is sufficient. The easiest way to find out is by making a call from your phone where you plan to install the antenna. You can also determine the signal level by the indicator on the gadget’s display.

Antenna installation

But besides this, there are other restrictions. For example, the place to install the amplifier should not be closer than a meter to heating appliances.

After planning the location of all components, begin laying the coaxial cable. But before turning on the repeater, you need to make sure that all connectors are intact and clean. Do not turn on the device if it is not connected to an external antenna, as it may be damaged. If you need to disconnect the RF cables, be sure to turn off the power.

There are also restrictions in temperature conditions. If for an external antenna it ranges from -40 to +50°C, then for the repeater itself it is limited only to positive temperatures. In addition, the repeater can only be installed in a heated room.

We must remember! An incorrectly assembled system can emit interference, which affects the operation of nearby stations. Therefore, you should not install it without examining the site and determining the location for all the blocks.

Amplifier settings

In order to obtain a stable and sufficiently strong communication signal at a specific facility, it is necessary to correctly perform all commissioning work. They consist of quality adjustment voice messages and eliminating self-excitation of the device.

We watch the video, what to do if the signal is bad, we look at the solutions:

The first thing to start with is to make sure that all connections are intact. The power adapter and antennas are connected to the high-frequency connectors. If power surges frequently occur in the network, then it is necessary to use a surge protector.

The next step is to adjust the gain. It must be at least 15 dB. The repeater can be configured manually or automatic control. In the first case, adjustment is carried out using the potentiometer knob and changing the position of the external and internal antennas.

Automatic tuning involves setting the gain level so that maximum output power is obtained. In this case, the device will independently adapt to the traffic of the operator’s base station.

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 radio receiver amplifiers with a large dynamic range of changes in the input signal, 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 the overload of the last stages of the receiver. In automatic radar target tracking systems, overloading the receiver cascades leads to distortion of amplitude modulation, a decrease in gain and failure of tracking. In frequency stabilization systems, overloading cascades causes a change in the slope of the discrimination characteristic, which sharply reduces the quality of system operation.

According to the principle of construction, AGC systems 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 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.

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

Rice. 2.2  Block diagram of an open-loop inertial

AGC systems

The timing system (Fig. 2.3) contains a control voltage generation device (VAG), the operation of which is synchronized in time by an external pulse.

Rice. 2.3  Block diagram of an open-loop temporary AGC system (a)

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

In practice, inertial AGC systems with feedback are most widespread (Fig. 2.5). They are divided into continuous and pulsed systems. All of the above systems can be delayed or undelayed.

Rice. 2.4 Structural diagrams of continuous AGC systems

with feedback (a) - non-amplified with combined detection, (b) – non-amplified with separate detection

The operating principle of the AGC system is as follows. Input voltage U in( t) is fed to the input of an amplifier with adjustable gain. The output voltage from the amplifier is supplied to the detector input, then the detected signal is summed with the delay voltage U h. Total voltage U c is amplified by a direct current amplifier (DCA) and fed to a low pass filter (LPF), the LPF generates the control voltage U y, changing 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 – gain at control voltage equal to zero;

 – slope of the adjustment characteristic.

Rice. 2.5  Functional diagram of the enhanced delayed system

AGC with feedback

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

To prevent a decrease in the output signal level at small input influences and ensure 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 d – detector transmission coefficient.

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

AGC system output voltage

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

(2.0)

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

at u d< u h;

at u d  u z, (2.0)

Where k upt – gain factor of the UPT.

Rice. 2.6  Block diagram of the AGC system

with feedback

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

Rice. 2.7  Amplitude characteristics of the AGC system

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