The reception system of a digital television signal

Preface

Referring to my previous article A useful handbook on digital terrestrial television in which I analyzed the digital terrestrial system, from production to transmission, and then to the reception, with this article I will analyze and describe in detail a reception system. These systems will be considered both for a single unit and for more units in the centralized form. I will start with the description and analysis of various components, then i will discuss the signal distribution, to conclude with the final design and installation.

This discussion is aimed at all professionals, particularly with regard to those who are passionate about DIY (do it yourself) and want to personally engage in the realization or modification of its television system. Unlike the now obsolete analog television system, the new European standard for digital television broadcasts via ground DVBT (Digital Terrestrial VideoBrodcasting) uses a binary system with the transmission of information packages.

This means that the main feature of a digital television signal is that of having the prevalence of quality compared to the intensity.

In practice, if the logic information 1/0 has sufficient quality to be recognized by the decoding system all the way from production to the TV input of user, then the signal is correctly reconstructed and made ​​visible. If, instead, the logic information is particularly deteriorated, then the image can not be processed and therefore you can not see any image. Basically, the TV picture will always be either visible and of good quality or totally absent.

The components of a reception system

In order to obtain a signal of good quality and, above all, constant in time, is of fundamental importance to know the function and the technical characteristics of all the components that are part of a reception system. These components can be divided into three categories:

– Active components. This category includes all those components that allow an increase of the output signal with respect to that applied to the input by means of suitable mechanical devices and / or electronic. The antennas, preamplifiers, amplifiers, power head, are part of this category; – Passive components. This category includes all components whose use in the system introduces a signal loss even if small and negligible. Cable distribution, filters, attenuators, the dividers, the shunts, connectors, sockets are part of this category.   – Accessory components. This category includes all those components that play a role in supporting the active and passive components without affecting the signal. The supports and bracing for the antennas, the conduits and junction boxes for the distribution of the signal, the power supplies are part of this category.

Active components

The antenna is the main component that characterizes a good television system since it must be able to receive only the useful signal to the distribution, strongly attenuating any noise or unwanted signals coming from other directions. In practice, the antenna is a component that amplifies and converts the electromagnetic field radiated by the transmitting into a voltage to be applied to the input connector of the TV. In addition, through appropriate design features, especially mechanics, it is possible to make it directive.

The element that allows this transformation is the dipole, which suitably dimensioned in function of the reception frequency, is connected to the receiver via the coaxial cable. It can be achieved in various forms such as open or folded and must be oriented perpendicularly to the plane of origin of the signal. Figure 1 shows some types of dipoles while figure 2 shows some types of antennas.

Regarding the antenna, you should keep in mind that according to the principle of reciprocity, there are no specific antennas for analogue or digital signals, and in the same way, antennas for only reception or transmission. To make a correct choice, you should refer only to the following features that must be reported by the manufacturer with appropriate documentation (see Figure 3):   – Frequency of use. In function of the reception frequency, can distinguish between the antennas used for single channel reception of only one television channel and the broadband antennas used for the reception of more television channels. With regard to this feature a particular type of antenna is the log periodic which has the particularity of having a very wide frequency band from 45 to 860 MHz. Conversely, however, it presents a low gain and a very large opening angle (greater than 60°). These are characteristics that make it usable only for the reception of signals of strong intensity coming from the same direction and in the total absence of reflections and interferences;  

– gain. It is defined as the ratio between the received power in a given direction and the power received by an isotropic antenna. The gain variation as a function of the direction of arrival of the signal is obtained from the diagrams of radiation provided by the manufacturer. According to this feature, the gain is greater the more the antenna is directive;

– opening angle. It is the angle formed by two directions (left and right with respect to the direction of maximum reception or transmission) corresponding to a decrease of the signal of 3 dB in power, 6 dB in voltage. For example, the maximum signal 80dBμV direction 275 °, 290 ° direction signal 74dBμV, direction 260 ° signal 74dBμV, opening angle of the antenna 290-260 = 30°;

– ratio forward/backward. It is the ratio between the gain measured in the direction of maximum reception and that measured by rotating the antenna by 180 °. It is expressed in dB and is a parameter that depends exclusively on the constructional characteristics of the antenna. In practice, it indicates how the antenna is able to attenuate any noise coming from the opposite direction to that of maximum reception. Along with the opening angle, it describes the degree of directivity of the antenna;

– wind loading stress. Itis the resistance that the antenna presents to the wind, is expressed in kilograms (kg) or Newton (N) and is an indispensable value to determine the size of the support and any bracing systems.

The Headend is the set of all equipment placed between the antenna and the distribution network. Its function is to adapt the signal you want to receive from the TV socket with the type and extent of the distribution network. This can be done using mixers, demixers, filters, converters channel, preamplifiers and integrated amplifiers.

Passive components

The coaxial cable is the element used for the transport of the electrical signal received from the antenna to the input connector of the TV. This is the most important passive component because it must ensure the quality of the signal in time and for its entire length. In practice, the cable is the means of transport of the signal with which the system connects the antenna with all other components, including the input connector on the TV. The coaxial cable consists of the following elements (see Figure 4):

– Inner conductor. Generally, it is made up of annealed copper or tinned copper as well as aluminum and steel can be used. This element is crucial for the attenuation of the cable. In fact, the larger the diameter the lower the attenuation;

– Dielectric. Made of rigid insulating material (usually expanded polyethylene) which ensures a constant ratio between the diameter of the inner conductor and the outer one in order to ensure a constant impedance along the length of the cable;

– Tape. It is made up of copper or aluminum and constitutes the high frequency shielding. In the best cables, it is coupled with a layer of polyester to prevent when the cable is bent, tears or cracks occur on the tape;

– Braid or outer conductor. It is made with copper wires suitably intertwined by means of industrial machinery that use a given number of spools (16 or 24). It is the second most effective shielding against interference at low frequencies. The standard EN 50117 for the coaxial cable used in the frequency range 30 MHz to 3 GHz has introduced “the class screening” identified with the parameter SA (Screening Attenuation) expressed in dB and defined as the ability of the screen to prevent both the irradiation to the outside of electromagnetic fields, both to external electromagnetic fields to disrupt the signal within the cable (see Figure 5);

– Outer sheath. It has the function to protect the cable from external agents such as water, sunlight, chemical agents. It is made ​​of:

• PVC is a soft protective sheath makes the cable flexible and easy to handle. Its vulnerability to all weather conditions makes it suitable only for indoor installations;
• PE is a protective sheath resistant to all weather conditions and is waterproof. It is suitable for outdoor and/or underground installations. Its rigidity also makes it walkable;
• LSZH (Low Smoke Zero Halogen) is a thermoplastic sheath with low emission of smoke and toxic gases particularly suitable for places like hospitals, schools, hotels, shopping malls, etc..

The main features that must be analyzed for the correct choice of a coaxial cable are:

• the attenuation expressed in dB per 100 meters at a temperature of 20 ° C;
• the class of shielding expressed in dB and identified with SA (attenuation of shielding);
• the capacity corresponds to the amount of electric charge that accumulates between the central conductor and the screen in a meter of length. It is expressed in pF per meter and must be as small as possible;
• the impedance that with regard to the television reception, has been standardized to 75Ω;
• the minimum radius of curvature that generally must be equal to or greater than 5 times the outer diameter of the cable. Figures 6 and 7, as an example, show the technical sheets of two coaxial cables in the Fracarro catalog, one suitable for indoors and one for outdoors.

The connector

Although many components are still available with clamp connections (absolutely inadvisable in digital reception), see Figure 8, the use of connectors is of great importance for a proper connection of the cable with the various components of the system. The “F” is the most widely used type of connector. This type is available in the market in two versions:

• screw (see Figure 9), it is very easy to install, economical and reliable;
• compression (crimp), (see Figure 10), it is much more reliable and much more technically valid, however, it is necessary to mount a specific tool.

Figure 11 shows the main types of adapters of this type of connector.

The Divider

It is a component that divides the signal into equal parts keeping unchanged the impedance. It introduces a low-loss between the various outputs but has a low attenuation of separation so that any noise present on the line is slightly attenuated. For these reasons, the divisor is only used to divide equally any distribution lines, especially in large centralized plants condominium. 

Currently on the market, you can find splitters up to 8 outputs with the following features: the insertion loss or division according to the frequency and the number of divisions is so much higher as higher is the number of outputs; the attenuation of separation is a function of the number of divisions of the frequency and typically not more than 25 dB, in the event a line is not used must be terminated with a resistance of 75 Ω in order not to unbalance the division;

The shunt

It is a component that must be used in cascade on a main distribution line and is characterized by an input, an output and some lines derived. Figure 12 shows the diagram of a two-way shunt.

If it is not used, this type of component must have the output connector terminated with a resistance of 75 ohms. The shunt is the component that must be used for the signal distribution to the various outlets in that it allows a separation from the riser so that any interference caused by a single TV is not distributed on the entire installation.

On the market, you can find shunts up to 8 derived outputs. They are characterized by the following parameters in function of the frequency:

• insertion loss or of transition dependent on the number of derivations and generally not more than 6 dB;
• loss of derivation parameter dependent on the manufacturer’s catalog for example that shunts FTE provides two-way junction with losses of 10, 12, 15, 20, 25, 30 dB;
• attenuation of separation between output and derivation in some types can reach up to 45 dB.

Figure 13 and 14 show the technical characteristics of Fracarro splitters and shunts.

Filters

They are components that can be used to pass or block a single frequency or entire bands. With the introduction of the new standard LTE (Long Term Evolution) about networks for mobile devices of 4G new generation, frequencies from 791 MHz to 862, that were previously allocated to UHF channels 61-69, are now reserved for broadcasts LTE.

From 1 January 2014 the telephone repeaters located throughout the national territory and the new phones transmit on these frequencies. When these transmitters will definitely running, all those who live in the immediate vicinity of the transmitters LTE and all those who use home networks LTE, will certainly review the antenna systems by introducing a specific band-stop filter (LTE) in the vicinity of the receiving antenna and / or socket of the TV. This problem can also affect all users that will use LTE phones in the vicinity of TV sets. In this regard, the standard IEC 100-7 provides the use of filters LTE in all television systems. Figure 15 shows the spectrum of the visible band LTE.

Attenuators

These components are quite similar to the filters with the difference that introduce only a certain attenuation value in dB. They are used exclusively to attenuate signals when they are too strong.

Outlets

They are the final components of the system of reception and in most cases it is the point where the cable undergoes twisting and crushing which can greatly impair the quality of the signal. The outlets can be either plain or terminal. In Figure 16 you can see the correct way of disposal of the coaxial cable inside the box containing the TV socket.

The components accessories

The Supports

They concern the supporting structure on which to mount the antenna and depending on the logistic situations they may be of various shapes and sizes. Typically they are made from a metal pole telescopic hot galvanized steel. It is firmly secured to the wall structure through special brackets walled or fixed with bolts. The main task of a good backup is to withstand the stresses of the wind; for this reason, in case of installing multiple antennas, during the design phase of the system you have to calculate the bending moment according to the characteristics of the antennas to be mounted. In addition to this feature, for the realization of a good support you must carefully evaluate also the possibility of free access in total safety in all the operations of installation and maintenance.

The Bracings

They must be used in all those situations where it is not possible to realize the supports which do not provide sufficient guarantees of resistance to wind loads. In practice it is necessary to place a group of braces every two meters of the support. The group should include three bracing placed at 120° hooked to the pole with a special turntable (see Figure 17).

The pipelines and junction boxes

A reception system in a workmanlike requires pipelines and junction boxes dedicated exclusively to the signal distribution. In particular the diameter of the pipelines walled or view must not be less than 25mm in order not to subject the coaxial cable to excessive mechanical stress during installation. In addition, junction boxes must be easily identifiable by a special plate and / or planimetric description. For the purpose of proper installation of the various components (splitters, filters, attenuators, shunts), in compliance with the maximum curvature of the coaxial cables and the maximum number of tubes, it is advisable to install junction boxes not less than the PT6 classification as shown in Table 1.

Power supplies

They are electronic devices that have the task of powering the active components such as preamplifiers and amplifiers and/or any filters or converters. They are mainly used for power components installed on the support and very close to the antenna. In general, they provide a maximum current of about 200 mA and are equipped with self-resetting protection against short-circuit. For the transport of the supply voltage the coaxial cable of descent is used (see figure 18).

The regulations in this regard

The main rule governing the receipt and distribution of television signals is the IEC 100-7. This regulation, along with the variant V1 in July 2013, completely replaces the previous 02/2005 and Appendix A of 05/2006 regulations.

The guide examines the requirements of functionality and safety of facilities for television reception with particular attention to the design, installation and testing. The systems are considered from the antenna to the socket in residential environment and similar.

The main new features of this version are:

• Requirements for the fiber optic distribution, definition of electrical characteristics of the signals received by the antenna in order to optimize the quality of the signals supplied to the outlets of the user;
• Definition of electrical characteristics of the signals distributed within the housing by means of the Home Network Interface in order to permit the design and the construction of the apartment such as to guarantee signals with specified quality;
• New criteria for risk assessment and requirements for protection against lightning;
• Information about the coexistence of plants of digital TV reception with the LTE mobile service. In this regard, the regulations state that every component that integrates both active and passive filter LTE must be provided with the manufacturer’s declaration certifying the compliance to the specifications prescribed by the standard.

The IEC 100-7 in the final part contains a number of recommendations directed mainly to installers, among which the most important are:

• In installations condominium centralized you have to build a compartment or a recess in the immediate vicinity of the antenna, with a power line network coming directly from the general framework, in order to contain the switchboard or the headend with the possibility of future expansions and a number of at least four tubes with a diameter of 40mm from the support antenna;
• You have to implement the system of fixing the antenna pole in such a way that in the future we can easily replace the tube without interfering with masonry work;
• Avoid creating boring easement of passage such as the use of private terraces or distribution ducts that pass through the apartments;
• accomplish the distribution of the signal up to the user point with appropriate piping and junction boxes dedicated exclusively to the distribution of television signals;
• In order to allow interactivity with devices such as computers and TVs of the latest generation, it is advisable to have a phone jack near every television outlet;
• In presence of the shops on the ground floor, it is advisable to arrange for a direct pipe to each compartment or niche in the vicinity of the antenna; 
• It is advisable to prepare a pipeline between the door station and a junction box TV in order to be able to send the images from the video door on televisions;

Ministerial Decree 22/01/2013 “technical regulations relating to installations condominium centralized antenna receivers broadcasting service”;

Radio and digital television, interactive, high-definition TV and 3D, A Practical Guide to User published 01/01/2014 made ​​by the Technical Committee 100 of the CEI in collaboration with RAI;

Directive 2011/65 / EC RoHS (Restriction of Hazardous Substances) on the restriction of use of hazardous substances in electrical and electronic equipment;

CEI 100-140 Guide to the selection and installation of supports antenna for television reception;

CEI 46-13 Cables for radio frequencies. General requirements and tests for individual coaxial cables for use in cable distribution systems;

CEI 64-50 Guide for the building integration of the electrical plants, auxiliary and telephone;

CEI EN 60728-4 Equipment for Cable networks for television signals, sound signals and interactive services. Passive wideband equipment for cable networks with coaxial cables;

EN 50083 Cable distribution systems for television and sound signals;

CEI 81-10 / 1-4 Protection against lightning; and the classification of the set of rules EN62305-1 General principles EN 62305-2 Risk Assessment, EN 62305-3 Physical damage to structures and injury to persons, EN 62305-4 Electrical and electronic structures;

CEI EN 50117 Efficiency of coaxial cables;

CEI 64-8 part relating to the laying of cables, coexistence with other cables;

CEI 81-2 Guide for the verification of the protection measures against lightning;

IEC 60169 Radio-frequency connectors.

Some examples

Example 1: design of a system for single-family detached house on three levels

Step 1: Following the inspection, the following data were collected: the majority of the programs comes from the same direction of 325 ° in the UHF band with an intensity between 88 and 93dBμV measured with antenna Fracarro Sigma 6HD connected to the instrument with 5 meters of cable coaxial Fracarro PAS4016. The installation location of the antenna is reachable and accessible in a convenient and secure. The transmission station is perfectly visible. Zone antenna installation with frequent presence of wind and storms. The client requires a television outlet in any room in the specific kitchen, living room, study, garden gazebo, garage, cottage, 4 bedrooms.

Step 2: choice of the distribution system and components. Analyzed the plan, you decide to divide the system into three main categories:

• Line the night with four sockets, one for each bedroom;
• Line day with four outlets, kitchen, living room, study and outdoor gazebo;
• Rustic line with two sockets for a garage and one for the rustic living room.

Using the following components and is realized Fracarro the diagram of Figure 19:

• # 1 antenna Sigma 6HD
• # 1 telescopic pole PTP4-42 height 3.80 m and diameter 35 to 42 mm for windy areas
• 105 m of coaxial cable PAS4016
• # 1 divider PA3
• # 3 shunts DE2-10
• # 10 terminal sockets SPI00 attenuation 0.5dB
• # 3 load resistors 75Ω CA75F

Step 3. Size distribution and verification of the signal at 470 MHz and, incidentally, to 790 MHz under the following conditions:

1. we calculate the attenuation of the farthest outlet (garage) from the entrance of the divider PA3:

• PA3 insertion loss = 8 dB
• attenuation of 14 m of cable = 2.03 (2.6) dB
• attenuation of DE2-10 derivation = 10 dB
• attenuation of 6 m cable = 0.87 (1.12) dB
• attenuation of SPI00 outlet = 0.5 dB

          Total attenuation of the farthest socket = 8 + 2,03(2,6) + 10 + 0,87(1,12) + 0,5 = 21,4(22,2) dB

1. we calculate the attenuation of the nearest outlet (Room 3) starting from the input of the divider PA3:

• insertion loss PA3 = 8 dB
• attenuation of 6 m cable = 0.87 (1.12) dB
• attenuation of DE4-10 = 10 dB
• attenuation of 4 m cable = 0.58 (0.74) dB
• attenuation of the SPI00 outlet = 0.5 dB

          Total attenuation of the nearest socket = 8 + 0,87(1,12) + 10 + 0,58(0,74) + 0,5 = 19,95(20,36) dB

1. You can easily verify that the difference between the attenuation to the outlet farthest and the nearest is not more than 15 dB, in this case: 21,4(22,2) – 19,95(20,36) = 1,45(1,84)                                                                                            
2. we calculate the signal to all other sockets from divider PA3:

• rustic = 20.82 (21.46)
• gazebo = 21.11 (21.85)
• cuisine = 21.11 (21.98)
• study = 21.11 (21.85)
• lounge = 20.82 (21.48)
• Room1 = 20.24 (20.74)
• Room2 = 20.53 (21.11)
• Room4 = 20.24 (20.74)

1. You can check that the signal at outlets is not less than 55dBuV and not exceeding 80dBuV, in this case:

• signal antenna = 88 ÷ 93 dBuV
• difference of attuenuation of cable connecting antenna (5 m) = 0.7 (0.9) dB
• attenuation distribution = 19.95 (20.36) dB

          Maximum signal at the outlets 93 – 0,7(0,9) – 19.95(20,36) = 72,35(71,74) dBuV

          Minimum signal at the outlets 88 – 0,7(0,9) – 19,95(20,36) = 67,35(66,74) dBuV

Fase 4. Simplified calculation for the evaluation of the risk of electrocution, to apply this simplified procedure is necessary to calculate the following parameters:

– N_d Expressed in number of lightning strikes per year, it is the frequency of direct lightning strike considering the height of the structure without the presence of the antenna, its value is given by

N_d = N_t · C · A · 10^-6

N_t = ground flash density for the area in antenna installation in our case 1.5

C = environmental factor obtained from table G1 CEI 81-10, in our case 0.25

A = collection area to direct strike of the isolated structure, expressed in m² and given by the relation

(L · W) + (6 · H · (L+W)) + (9 · π · H²),

In our case, the structure has length L 18 m, and width W 12 m. H is the height of the structure without antenna 7 m, then A = 2861.4015 m², thus

N_d = 0,0011

–       N_d1 is expressed in number of lightning strikes per year, it is the frequency of direct lightning strike of the structure considering the height of the structure including the antenna. The calculation procedure is the same as Nd considering the value equal to the height of the structure plus 10 meters (7m and 3m for the height of the antenna), consequently

N_d1 = 0,0018

–       N_a is the value of the frequency of lightning strikes tolerable obtained from table G2 of CEI 81-10. In our case class B building, civil housing with fire hazard ordinary

N_a = 0,050.

Because the values ​​of  N_d and N_d1 are less than the value of N_a, the structure with or without antenna is self-protected and does not need any protection from direct lightning strikes. is appropriate, however, especially for the frequent presence of temporal, provide protection of the user sockets surge through the use of SPD class III.

Example 2: design of a system of a six-storey building and 24 residential units

Step 1: Following an inspection, the following data were recorded: all the signals coming from the same direction of 165 ° in the UHF band with intensities between 80 and 85 dBuV detected with antenna FTE model HYDRA45LTE connected to the instrument with 5 meters of coaxial cable Cavel DG113. The installation location of the antenna is reachable and accessible in a convenient and secure way.

The area of ​​antenna installation poses no particular problem weathering. The transmission station is perfectly visible. The client requires three television outlets in each unit housing, specifically one in the living room, one in the master bedroom and one in the kitchen;Step 2: The choice of the distribution system and the components of the system: once analyzed the plan and following the requests of the client you decide to divide the system into two main lines laid in two risers, each serving 12 residential units . You decide to use the following components FTE maximal:

• # 1 antenna model HYDRA45LTE
• # 1 telescopic pole PT2502 2×2 m
• #1 amplifier MA3610
• 600 m of coaxial cable Cavel DG113
• # 1 divider AS2
• # 4 shunts AT230
• # 4 shunts AT225
• # 4 shunts AT220
• # 72 outlets through PP04
• # 2 load resistors AW75F

Step 3. Dimensioning of the distribution, verification of the signal (at 470 MHz and 800 MHz in parentheses) and the execution of the schema of the system with the same procedure described in the previous example. Get the following values​​, see Figure 20:

Input signal AS2 = 115 output level of the switchboard – 0.7 (1) attenuation 6m cabl = 114,3(114) dBuV

Signal at the nearest outlet 114,3(114) – 36(36,8) = 78,3(77,2) dBuV

Signal at the farthest 114,3(114) – 43,8(46,3) = 70,05(67,7) dBuV

Step 4: simplified calculation for the risk assessment of lightning with the same procedure described in the previous example with the following parameters: Nt = 2.5, C = 0.25, the size of the building length 24 m, width 20 m, height without antenna 22 m, antenna height of 25 m. You get the following values:

N_d = 0,019972

N_d1 = 0,02475

N_a = 0,050 Building Class B (residential) with ordinary fire hazard

Since the values ​​of N_d and N_d1 lower than the value of N_a, also in this case the structure with or without antenna is self-protected and does not require any protection from direct lightning strike, because of the insignificance of atmospheric phenomena the protection of user sockets is not deemed necessary with SPD class III.

Some practical tips

During the installation of a television system, the coaxial cable appears to be the most sensitive element. In fact, its electrical characteristics depend predominantly from the geometric structure of the various components. It is therefore of fundamental importance that are not altered during the installation and the assembly phase of the outlet by excessive traction, bending, crushing. Figure 21 shows the proper coupling to the probe traction that must obviously be suitably taped to cover the outer sheath.

Use plug-TV connections with high efficiency and of limited length. Indeed, most of the problems, especially in the domestic environment, are derived from these connections made often in an approximate manner and used in an improper way (see figure 22).

For the purpose of proper installation of the various components (splitters, filters, attenuators, splitters), in compliance with the maximum curvature of the coaxial cables and the maximum number of tubes attested, it is advisable to install junction boxes greater than or equal to the classification PT6 (Table 1 ) whose measurements provide a good margin of operation (see Figure 23).

The header connector is a very delicate operation that must be performed accurately and precisely. The phase of “stripping” must be made with very sharp tools, better if done with proper stripping of the type of cable used see Figure 24, avoiding the crush and impact damage to the screen and dielectric tape but above all we must be very careful the contact between the outer braid and the metal body of the connector. In this regard, once it has been folded on the outer sheath, keep it with the fingers of the hand and with the other screw the connector. Once you have completed screwing, cut off the excess. When you have completed the heading, it is advisable to tape the end of the connector and a piece of cable with self-amalgamating tape. Finally you need to run a light filing around the tip of the center conductor for easy insertion into the female connector, see Figure 25;

In most cases for the connection of the antenna connector with the headend or the entrance of the distribution (typically not exceeding a few tens of meters) cables are used with PVC outer sheath without any protection. This thermoplastic substance is not suitable for outdoor use when subjected to weathering and readily degradable and not fully waterproof. For this connection coaxial cables with a sheath of polyethylene (PE) should be used or you have to protect the connection with a pipe up to the heavy antenna connector.

Very often, especially in the home environment, you make the mistake of using the divider to increase the number of outlets due to their low attenuation. You should remember, however, that these components, because of their low attenuation of separation, must not be used for the leads on the end users. In a television system, unlike an electric system, the values ​​designed can be subjected to huge variations over time (formation of oxide in the connectors, atmospheric corrosion, deterioration of the values ​​of shielding cables of poor quality, infiltration of moisture) if the plant is not properly installed and can degrade quickly.

Law 220 of 13 December 2010 has limited the V-band UHF 790 MHz or up to channel 60, by allocating the channels 61-69 (791 ÷ 862 MHz) to the 4G mobile communication. The IEC 100-7 standard with the V1 has issued special technical specifications which must be met by those filters LTE to be installed immediately and by any other component that integrates the above filter.

According to the above, from 01/01/2014 all new installations both single and centralized, for the correspondence to the “rule of the art”, must be fitted with components with limited frequency band at 790 MHz while those installed before that date shall be equipped with filters LTE approved and fitted with the manufacturer’s test report (see Figure 26).

Even today, unfortunately installations visible in Figure 27 are very frequent. In this regard it should be specified that the support of the antennas without the need to design calculations can be realized up to a maximum length of six meters considered between the upper anchorage point and its top. Exceeded this limit the preparation of a project by a qualified technician regularly is necessary.

In the design or construction of a plant of television reception, the use of an amplifier must be mainly aimed at recovering all the losses of the distribution network and not to the improvement in signal intensity.

If the output signal from the antenna connector is less than 45 dBuV, no amplifier will be able to provide a valid support to distribution, indeed worsen surely receiving. In these cases it is necessary to study a system of combined multiple antennas able to bring the signal to an acceptable level. The best reception of the digital signal depends exclusively on the technical characteristics of the transmitting station, which is to serve a specific catchment area. Very often the signal reception, both in power and in quality, can be significantly different from building to building or between different neighborhoods. Sometimes it is sufficient to move the position of a few meters.

Precisely for these reasons that before making a reception system to make an inspection visual and instrument is of paramount importance (field strength meter or spectrum analyzer, antenna with known characteristics and coaxial cable attenuation note) in the exact spot where it should be placed the receiving antenna, in order to choose the most suitable type to the installation location.

The project documentation is another very important element for the proper testing of the system and especially for future interventions of preventive and corrective maintenance, but especially in the central house systems where the knowledge of the distribution is of fundamental importance for any intervention is in each unit and in the common areas.

Documentation must be composed of at least a brief technical report with the description of the various technical solutions adopted and a list of all the materials used, a diagram with the locations of the pipelines and the location of the junction boxes and all components, a detailed connection diagram.