Presented calculation of the amplification system cellular communications will confirm the correct selection of equipment and 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. Signal level at the location where it will be or has already been installed external antenna. 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 base station to a 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 characteristics (in our case, the 900SXB has Ku = 60 dB). We get at the amplifier output: -54 +60 = +6 dBm.
4. In the cable from the repeater to internal antenna at 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.

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.

1. Installation of an external antenna.

The first step is installation external antenna. The antenna is installed using fasteners (a swivel bracket or a mast) on the external wall of the building or on the roof, depending on the location.
The specialist determines the direction in which the antenna will be directed, since the incoming signal from different operators communication should be the same, or the signal of any particular operator should prevail if the goal was to improve the quality cellular signal only one operator.

2. Preparation and crimping of the cable.

At the ends of the prepared cable, you need to put on N-type connectors and crimp them (or prepare the cable in advance and solder the connector if it does not involve crimping). We recommend protecting the connector with heat shrink or tape, as it can oxidize over time, causing erratic operation and interference. Next, we connect our cable to the external antenna and move on to the next step.

3. Cable laying.

Everyone knows that when laying a cable, it is very important that the distance from the repeater to the external antenna should be minimal, since with a long cable there will be large signal losses (the amplitude of the incoming signal should be maximum). We choose a place for laying the cable, taking into account all the recommendations, lay it and proceed to repeater installation(cell phone booster).

4. Installation of a cellular signal amplifier.

The installation location of the repeater is selected based on the minimum length of the cable and so that it is not located in a visible place. This can be either an attic, if it is a private house, or the repeater is hidden above the ceiling, if it is an office building. But you need to make sure that the installation location complies with the permitted climatic conditions in the repeater’s passport.

5. Connecting an external antenna to the amplifier.

There are two connectors on the cellular repeater body. We will need a connector, which is designated by the letters BS - this is the amplifier input. We connect our cable from the external antenna, making sure that the connector is screwed in tightly and all the way.

6. Installation of the internal antenna.

Depending on the situation and the area of ​​the object, internal antennas maybe several.
If several antennas will be used, then it is necessary to install a signal splitter that will divide the power for each antenna. Next, you need to crimp the cable with connectors, as was done in the beginning, and connect it to the signal splitter and to the internal antennas. Signal splitter connect in a similar way to the second, free output of the amplifier. If only one internal antenna was used, it is connected directly to the repeater.

Poor cellular reception is a very common problem. Many people encounter it both at their summer cottages or in country houses, and in their own apartment within the city or village. Weak signal telephone number or its complete absence is primarily related to the remoteness of the base station of your mobile operator, building density or terrain.

If you are faced with this problem and high-quality reception is a vital necessity for you, you need to install a cellular communication amplifier. More precisely, you need a cellular communication amplification system in which such an amplifier is one of the devices. In general, the described system consists of the following “links”: a GSM repeater, an external antenna for receiving a cellular signal, power dividers, a connecting cable and the connectors necessary for connection.

Of course, choose similar system and, what’s more, installing it and properly configuring it can only be done by a specialist. However, so that you can get on the “right path”, we will try to understand a little about modern cellular signal boosters and which ones are better to choose.

Selecting a mobile signal booster

Before deciding and choosing the right GSM communication amplifier, you should understand the main technical characteristics of these systems:

• Cellular standardGSM mainly divided into two main bands: GSM 900 and GSM 1800 MHz. Base stations (cell towers) in the 900 MHz range have a greater range, but fewer channels (the ability to talk to several subscribers simultaneously) than at 1800 MHz. Therefore, 900 MHz base stations are more often used in the region, and 1800 MHz base stations are used within the city. Therefore, for a summer residence or country house It’s better to stick to the GSM 900 standard.
• Gain factor (GC) of the GSM signal amplifier is another important parameter for choosing a system, because it directly affects the level of network reception provided. Simply put, if your mobile phone has poor reception indoors, but outdoor reception is almost at the maximum level, then an amplifier with a gain of 70-75 dB is quite suitable for you. If your cellular reception is uncertain even in the area near your house, then you should take a closer look at a cellular amplification system with a coefficient of 75-90 dB. It is better not to purchase a cellular repeater with a gain of less than 65 dB at all, because... he is unlikely to cope with the task you set.
• Repeater output power mobile communication amplification systems. This parameter affects how much area of ​​the room your GSM signal amplification system can “cover” with reliable reception. For example, a cellular network amplifier with a power of 100 mW is capable of providing reliable reception to an area of ​​up to 200 sq.m, and a cellular repeater with a power of 320 mW can cope with a room of up to 800 sq.m. However, there is no direct relationship between the power of the repeater and the area of ​​your premises, but only the concept of correlation. A variety of factors can influence how GSM repeaters provide reliable reception to a specific area of ​​a room. For example, the level of the input signal from the cell tower, the length of the cable from the external antenna to the amplifier, the control unit, as well as the proper installation of all equipment as a whole.

At the moment, among repeaters for a country house, office, cottage or cottage, the most popular models are Picocell 900 SXL and Picocell 900 SXM.

• Picocell 900 SXL operates in the GSM 900 band. The gain of this system is 80 dB, and the output power of the repeater is 320 mW. The 900 SXL amplification system is intended for indoor installation only.
• Picocell 900 SXM has the same parameters as its younger brother Picocell 900SXL, however, this system is equipped with a cold and moisture resistant housing with an IP66 protection rating. This device is optimal in cases where it is not possible to lay the cable indoors and cellular amplifier GSM with its entire structure must be installed outdoors.

Choosing a quality external antenna

An external antenna is required to receive a signal from your cellular operator's base station. It is mounted on an ethereal mast installed on the roof of the building. It should be borne in mind that an external cellular antenna is constantly exposed to a variety of external factors (rain, snow, wind, etc.), so when choosing its model, you should pay special attention to reliability and durability. A fairly good option is the model AL-900-11, because it is made of a solid sheet of metal coated with enamel paint, which will reliably protect it from oxidation, corrosion and destruction.

Selecting Suitable Internal Antennas

The choice of these devices is directly related to what stage of construction your house or cottage is at. If the interior decoration of the room has not yet been carried out and you still have the opportunity to install an internal cellular antenna behind suspended ceilings, then it is worth purchasing a network of antennas with a fairly low gain. Thanks to this solution, you will have a uniform cellular signal coverage area. The preferred quantity is the ratio of one antenna for every 100 sq.m. area. Among these antenna models, I would like to recommend AP-800/2500-7/9ID. These antennas support all currently modern communication standards: GSM900, DCS1800 and even UMTS 2100 (3G).

If you need to provide a high-quality mobile signal inside a living space, and, at the same time, not disturb its interior, you should take a closer look at one antenna with a high gain. Such antennas, if possible, are installed in invisible places. Interesting models RAO-11GL-60 or RAO-14GL-70, which have a gain of 11 and 14 dB. This fairly high gain makes it possible to achieve the network coverage you need using one antenna.

Selecting cables and connectors for the system

All amplification system devices GSM networks are connected to each other by a coaxial radio frequency cable with a characteristic impedance of 50 Ohms. For a cottage or dacha, the best cable brands in terms of price and quality are 5D-FB or 8D-FB. The difference between them is the thickness of the central core and, therefore, the level of residual attenuation during the passage of the signal (5V-FB = 0.2 dB/m; 8V-FB = 0.13 dB/m at a frequency of 900 MHz). Taking into account the fact that modern cellular communication standards are increasingly using frequency range in gigahertz, it’s worth choosing an 8D-FB cable, because it is more promising.

The 5D-FB cable uses N-111/5D connectors, and the 8D-FB cable uses N-111/8D connectors.

Selecting Cellular Network Power Dividers

The power divider is designed to branch cables into a certain number of internal antennas. The most reliable and widespread models are Picocoupler And DirectionalCoupler. Picocoupler brand devices are designed to distribute the cellular signal evenly throughout the room with a different number of outputs for connecting antennas. DirectionalCoupler models are used to distribute the network signal unevenly.

As a result, if you have correctly selected all the devices, bought a cellular signal amplifier, installed and configured it, the general diagram and principle of operation of your system will look like this:

Keep in mind that when choosing a cellular signal booster system for an office, cottage or country house, you need to take into account specifications all its individual devices. At the same time, it is extremely important to select a high-quality GSM network repeater, ensure its correct operation (compatibility) with other devices and meet all the necessary requirements for ensuring high-quality and uninterrupted communication of the GSM and UMTS (3G) networks.

Compliance with required standards

When installing a GSM or 3G mobile communication amplifier, you should be aware that its poor-quality installation or configuration can have the opposite effect, and your system, as a result, instead of increasing signal reception from the BS, will, on the contrary, reduce it.

Moreover, any of the cellular operators - MTS, Beeline, MegaFon and others - have all the technical capabilities to detect the presence of interference for high-quality reception and distribution of radio waves from their base stations. Using special measuring equipment, engineers will determine the location of interference in the form of an incorrectly installed GSM amplifier.

After this, the owner of such a system will be warned about the need to reinstall, correct settings, or completely replace all equipment. If this warning is ignored, mobile operator has the right to file a complaint Radionadzor, which has all the powers to bring the unscrupulous owner of a GSM cellular network amplifier to administrative liability.

Keep in mind that any cellular signal booster, even if installed in the most competent manner, creates interference that interferes with the base station signal. However, there are certain standards, and if you do not exceed their maximum value, you should not have problems. However, for this it is important not only to skillfully install all the elements of equipment, but also to be able to configure it correctly.

Therefore, if you do not have the necessary knowledge on setting up GSM repeaters and installing them, it is better not to try to make a GSM signal amplifier with your own hands, but to use the services of specialists, of whom we now have more than enough.

Confident reception!