Basic elements in an installation of telecommunications
- In order to be able to communicate in the distance two points, we needed a series elements with major or minor complexity, but with technical details that we must very consider to have the best possible system. We will see each one of the elements, that they are:
- Cables of copper and fiber
- Duplexores and Diplexores
- Distributors and mixers
Electrical systems in stations of radio communications
- System in charge to receive the signal to transmit, to treat it and to feed the element in charge to transmit it (antenna). In the scheme of the right, one has omitted the blocks of filters. One of the audio system of (to filter the exit of the study) and another one would have to be added when coming out before feeding the antenna. The basic elements are
- Signal of audio of the studies. In this case, we have taken a transmitter from A.M. where a social gathering is being transmitted, music, etc. The exit must be treated so that the possible thing contains “a clean” signal but. It is obtained with systems of filters, and, by all means, with elements suitable translators (good cable microphones, systems, electronics of low noise, etc.
- Oscillator. A sine frequency given by the transmitter is generated. She is not always the same, since each transmitter of A.M. has hers. For example, we have National Radio of Spain in Madrid has a frequency of 585 Khz
- Once produced the carrying signal, one goes to an amplifier.
- The carrying signal and the signal of audio (of the study) go through the modulator so that, in this case, the signal of the carrier is modulated, agreed to the amplitude of the signal of the study
The resulting signal enters a radio frequency amplifier and this one feeds antena/li>
An important advance in the receivers was the incorporation of the receiving heterodyning.
To heterodyne (to obtain a frequency from the mixture of other two) has the intention to mix frequencies and to obtain one third signal with useful results in the stages following of the receiver
We show the basic scheme of this element
- Once the signal arrives at destiny, we have it signal that takes the antenna is given to the receiver, made up of a series of block that we detailed.
- Block of amplifier of the signal. The signal usually arrives with little power, thus is necessary component east.
- Local oscillator. According to he is the type of modulation, is necessary to create a sine signal of a certain frequency. This signal we are going it to enter next to the signal that comes from the antenna amplifier, to the mixer.
- Mixer. This component is going to us to create a signal of an intermediate frequency F3, giving rise to 2 F3 frequencies, that come to add and to reduce F2 and F1 (to see image).
- The filter of intermediate frequency has a narrow bandwidth but (reduced), giving rise to a greater selectivity of the set. The signal leaves list this block to be demodulated. It is a filter of high selectivity in frequency.
- The demodulador applies the appropriate technique (FM, A.M., etc) to obtain the signal that contains the information
Baseband amplifier. Once we have the demodulated signal, it is necessary to amplify it and to filter it for the power stage.
We can at greater length extend in the part inferior of the page (Receiving superheterodyne) 3º
- In this section we talked about to what half we are going to use “to lead the signal” from the origin to the destiny. That way can be guided or not be guided. In first we included to copper cables and fiber cables. In not guided, we spoke of the electromagnetic waves, that do not need any type of support to transmit themselves (they can travel in the emptiness) Within cables, the properties to which we will pay attention will be:
- Reliability of the cable
- Facility of the installation
- Speed of data transmission (Kbit/s)
- Bandwidth (whichever channels we can happen)
- Price of the cable
Space between repeaters in great facilities
3,1 copper Cables.
Within them, we mainly have cables of pairs and the coaxial one. For it, we already reviewed the sight within the page cable types of data and optical fiber (along with the material who we have in the book)
3,2 Coaxial cable.
It is constituted basically by an internal copper cable, a dielectric material, it enmeshes of copper and a cover that protects it. One of the most important aspects is the impedance of the cable, that depends on factors as the distance that exists between the inner cable and it enmeshes. For that reason it is very important that too much does not bend in order not to modify this parameter.
- The impedance comes as:
- Zo is the impedance of the cable, that does not depend on the length.
- εr is called the relative permeability of the dielectric and depends on the type of material (solid polythene, expanded polythene, etc)
- Of it is the diameter of the outer cable
I gave is the diameter of the inner cable
- To emphasize we have:
- In the real cases where the cable load with generators or receivers, whose impedance he is equal to the impedance characteristic of the cable, the impedance of this one remains constant.
- Zo of the cable is independent of the length of the same. This seems peculiar because it seems that to but cable but impedance, but we must consider that this consideration becomes for an ideal cable, with resistance of null copper.
- Also, and for a line without lost, the impedance is constant independent of the frequency.
- In an adapted good line in impedances, reflections of signals will not take place
When a cable with an equal impedance to the impedance of the load is connected, the energy transfer between cable and load is maximum
No, it is not a cable, IT IS the CABLE. With this, we want to emphasize the importance that has this element within a set, which apparently they are but important that the same cable. It is very important that all the blocks that are connected to the cable have identical impedances to which has the same cable so that reflected waves do not exist and the yield of the set is maximum.
The majority of cables has an impedance of 50 or 75 Ohms. We leave an image of the electrical equivalent of the coaxial one
If we compared it with the twisted pair, we have, generally to day of today (in this always we must mark dates, end of the 2017)
- Other characteristics are:
- It is possible to be used to cover majors distances.
- As a result of the previous thing, the sections between stations (repeating) can have major distances.
- Thanks to his screening, he is less susceptible to interferences.
It offers major frequency of work and major speed of transmission.
For example, we have the broadband coaxial cable, that normally is used for the shipment of the cable TV signal, can get to have 100km of distance. If we make it work to 300 Mhz, Mbps gets to have 150 speeds of.
3,3 optical fiber Cable
- A this transmission medium are very used in telecommunications and systems of data networks, that are made of a very fine thread of material transparency, (material plastics or of glass) and through which they pass the pulses of light (data aque are wanted to transmit). That beam of light is confined within the fiber, propagating by the interior with an suitable angle of reflection, inferior to the angle limit of total reflection, that can be calculated by the equation of Snell. We see it in the following illustration
the luminous source can be generated by laser or a diode LED. At the moment it is the means by more advanced cable and with greater bet in the sector of the telecos, given the advantages that we are going to enumerate
- High bandwidth (of the order of the GHz).
Small size of the fiber (not only of complete cable)
- Relative flexibility, with radii of curvature on the rank of 3 to 7 cm. This is an advantage in the facilities. One is due to look at the characteristics of the manufacturer to take the real value. A approximate rule is to take the measurement from the diameter external of the Cable and multiplied 20 times, that is to say, Rc = 20 xs Dc (where Dc is the external Diameter of the cable).
- Great lightness. Km is 9 times less heavy than the corresponding one in copper
- Total Immunity against electromagnetic disturbances. Neither the storms, nor the startings of motors are going to disturb the transit of data by the fiber
- High security. In case of electrical signals by a driver, the taking of a sample to look around what is transmitted by that network is hardly detectable. In case of the fiber, that intrusion supposes a weakening of the luminance energy in reception, which serves as alarm. If we want confidentiality, optical fiber
- It does not generate interferences.
- The attenuation is very small and independent of the frequency of the beam. This supposes that we can cover long distances before using some active element (amplifying laser)
- Ample margin of operating temperature
- Immune to the corrosion.
Thanks to the use of the technique of the reflectometría, we can locate the cuts of the cable. In the sea, there are thousands of km of fiber. This allows to solve problems very quickly, in case some “fish is hooked to facebook”.
We will now see two videos on fiber.
1º Taken care of the optical fiber
2º reflectómetro optician (OTDR)
It is possible to be produced changes in the attenuation. because the hydrogen molecules get to spread in silicon fibers.
- But everything has its disadvantages
- Fragility of fibers (breakage by impacts)
- More expensive transmitters and receivers.
- In order to unite fibers it is necessary special equipment (fusionadoras) and technicians preparations in these tasks.
- They are not possible to be used to feed intermediate repeaters, since the fiber is not driver. The energy must be provided by separated drivers.
- In many cases we must make several processes of electrical-optical conversion.
- The conventional optical fiber cannot transmit high powers.
Windows of transmission of the optical fiber:
They are called thus to the wavelengths (λ) of the light that use the emitters. To them usually it is called windows and come represented in the figure following
Activity. In the previous graph, it explains because frequency 1450 is not used nm.
Activity. Because window in connections of great distance is but advantageous to use 3º
Something that we must know within the fibers is the MODAL DISPERSION that is a characteristic of they have fibers multiway and that cause that the bandwidth is limited, since the different ways from light cross different ways within the optical fiber. We leave an illustration of this effect, where we can see how, as a example, a white light of entrance (whose main components are the blue one, green and red) has three ways (one by each color) arriving the blue light before the rest. The red light, by the trajectory that takes, arrives later that the rest. This problem is solved using fibers with nuclei with variable refractive index
The different ways that the light follows inside a fiber denominate modes of propagation. According to the mode of propagation, the fiber classifies in multiway and monoway.
In this fiber, the light beams can circulate around several ways. As each way has a distance different between the principle and end from the fiber, the beams do not arrive all simultaneously. These fibers are used in applications of distances smaller to 2 km, being simple to design and economic, they are easier to connect and has a greater tolerance to components of little precision.
- According to the refractive index of the nucleus, there are two fiber types multiway:
- Fiber of stepped Index: Where the nucleus has a constant refractive index in all the cylindrical section, it has discharge modal dispersion.
Fiber of gradual Index. In this case, the refractive index is not constant since the nucleus is constituted of different materials. It has minor modal dispersion.
- According to system ISO 11801, we have:
- OM1: Fiber 62,5/125 µm. The USA LED as emitters. Speeds of Gigabit Ethernet (1 Gbit/s),
- OM2: Fiber 50/125 µm. The USA LED as emitters. It supports until Gigabit Ethernet, just as OM1
OM3: Fiber 50/125 µm. it uses laser (VCSEL) as emitters. Gigabit Ethernet supports up to 10
- Fiber monoway
- The light only propagates a light way., thanks reducing the root diameter of the fiber (8.3 to 10 microns)
- Its transmission is parallel to the axis of the fiber.
- In contrast to the multiways, the fibers monoway allow to reach distances of 400 km by means of a laser of high intensity
Lifted rates of information (10 Gbit/s).
Fusion of fibers and types of connectors
1º Vamos to see a video on the use of the fusionadora.
2º Tenemos to remember the fiber connectors in the connection Installation of radio elements
3º Veremos how a clich3e with one of the connectors is created that we have in the Infrastructure page of the data networks
Pages of interest 1. - https://www.monografias.com/trabajos108/transmision-fibra-optica/transmision-fibra-optica.shtml
2. - Optical fiber in ICT. https://sites.google.com/site/desarrollosticaura/proyecto-de-ict/stdp-y-tba/4-fibra-optica
|Comparative between means
||Speed in bits/secondly
|Distance to another repeater
When we must use the space as half of connection between emitter and adressee, we will vice versa make use of an element that is going to us to translate an electrical current in an electromagnetic field and. We will follow this section in the connection Basic principles of antennas
5 Duplexores and Diplexores
A duplexor is a component of radio communications that allows to use a same antenna as much to receive as to emit, disconnect the emitting and receiving part of the station. In the image of the left we have this component represented in green, taking place in the same the commutations to allow that the transmitter sends the signal to the antenna, or, that the receiver receives the signal of the antenna.
The Diplexor makes the same task, but with the difference that connects equipment of different work frequently, for example, when we must use frequencies of satellite and terrestrial TV, as we showed in the following illustration
6º Distributing and mixer
The purpose of the distributor is to distribute the signal in the points that are necessary (for example when from the tile roof of a back-to-back one, we have two plants with several points of TV). In case that distributor (or distributor) is passive (without feeding), a lost one of 3 is had dB by each taking, that is to say, for a distributor of 4 exits, we have 12 a total losses of dB. The mixer makes the inverse function.
Not to confuse a distributor with a derivador.
The derivador makes the same function that the distributor, but the exits have different losses, for example, in one of three exits, we can have 3, 6 and 9 db
7º Electrical system in stations of radio communications
This section is contemplated very well in other modules of the cycle. We will make a revision on the most important aspects at the time of being able to provide necessary the electrical energy for the process of radio communications.
In case 2 it is possible to be chosen to install solar panels or aerogenerators, always supported by SAI
- The station must at any moment have a constant flow and of quality of electrical energy that will be provided from different sources. We will have to consider the environmental criteria, from access to the station, the renewable energies that we have in the place, of the surrounding electrical laying, etc. On the basis of those and other criteria, we will make the best decision. We will put several cases in which we will be able to act
- In the zone we have electrical light of some company. In this case it is the best option of all, since the voltage drop in the lines rarely happens and the response times have been increased much. That situation can be complemented with systems SAI so that, in case of failure of the electricity provision, the radio communication does not fall. We will have to consider the calculation of batteries.
- Zones difficult and without electricity. In this case, we decided on renewable energies if it is possible or by generator sets. In the case of the groups we must consider that it is necessary a deposit for the gasohol, in addition to systems of air conditioning, security, fence complete of the enclosure, acoustic contamination of the surroundings, etc.
Activities. To complete this section with the references that we have in the book
1º an installation says that it is very available when it has service 99.999% of the time with service. We have found a fall of 20 minutes throughout the year. They have fulfilled the fiance?
2º Tenemos a solar station that, for the night we needed a provision 600 Ah. The batteries have a tension of 12 volts and 80 Ah. To calculate whatever and how they will go connected
3º What contributes to have an intermediate-frequency amplifier in a superheterodyne receiver?
4º Calcular the impedance of a cable with permeability 1.8 and whose greater diameter is three times greater than the smaller diameter
5º asks to Us that we mount a satellite dish in a house, but the tube already is occupied by an antenna cable and there is but no space. What solution you can give him?
6º Busca in Internet the radiation pattern of a used antenna to give cover of UMTS in the city
7º the generator sets produces AC voltage and, nevertheless, the equipment of radio communications needs DC. That it will be necessary?
8º an antenna has a yield of 80%. If the contributed power is of 2 W, to calculate the broadcast power
To show for knowing something more on the superheterodyne receiver
We will see summarized way how this receiver works. We have divided it in two zones. A first in red and 2º detailed and improved receiver but. It is only necessary to study the summarized one (in red).
1º All the frequencies of the radio waveses arrive at the antennas of our receiver. The first amplifier of RF (radio-frequency amplifier) increases to the signals between 80Mhz and 110Mhz, (for the case of FM, clearly), although the real band of FM is included enters 88Mhz 108Mhz. If we spoke of A.M., the band would be between 500Khz and 1800Khz. Everything what is outside those frequencies, the RF amplifier rejects it.
To consider that always in our schemes, the task of cleaning and of leaking we do it incorporating a filter. In the image of down, this task already makes that amplifier, for that reason it puts amplifier passband
2º When advancing, we have a local oscillator, that generates a variable frequency, according to adjusts the syntony block (manual or synthesized PLL). That frequency arrives at the mixer and it is mixed with the frequencies that arrive to him by their other entrance, being generated multiple frequencies when coming out of the mixer. In the example of down, we took a frequency from local oscillator of 106.8Mhz, giving rise to an Array of frequencies turn out to add and to reduce the frequency that comes by the air and the generated one in the oscillator. All of them are going to enter in the following stage.3º As much the resulting frequencies of the sum (F3 = F2 + F1) as the one of the subtraction (F3 = F2 - F1) will be entered the intermediate-frequency amplifier
4º Now we were again with an intermediate-frequency amplifier with filter band, tuned to 10.7Mhz. If we phelp attention to the table of frequencies that there are in the image, in green we have that 10.7 fruit of the subtraction of the frequency of 1º oscillating with another one of the “air”. It is that frequency of 96.1, the one that we are going to be able to be in tune, being the rest annulled by that amplifier of FI the great advantage that we have with this receiver is the great selectivity, with the rejection to frequencies that do not agree with the step channel (equations in red color)