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Systems of radio communications

 In order to review the concepts, we are going to review a pair of times this work on signals and waves that we can see in

This presentation you have them in pdf in the shared folder of DRIVE

 Equation of transmission of Friis.

This equation will be seen ahead but given the importance that it has in the telecommunications (radio I connect). There are many forms to indicate it and, for this reason, the best thing is to use it of the direct way, deducing the Db received, from the formula: , where Pt is the transmitted power, Gt the gain of the antenna that it transmits, gr. the gain of the receiving antenna, moor is the wavelength of the signal and R the distance that separates receiver emitter.

equation friis

In the previous presentation, was a relation as it is in the image

The author uses the Lfs term to indicate the loss of the system in dBm. We are going to demonstrate because it leaves that term in the section Knowing more (it can enter examination)

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friis 1

Lfs as log of the relation between transmitted and received Power is defined. We apply the equation of friis and it does not give:

friis 2

Also we know that to the relation between the speed of the light and wavelength, comes dice by c = λ/T (with λ T and the wavelength the period, that is the inverse one of the frequency. Therefore, λ as c/f can be replaced. The previous expression we have left:

Now, we continued moving terms, but we are going to pass the meters of r (distance) to km and Hertz to GHz. In the case of the distance, we have left r= 103 km.

When high being to the squared one, that expression stays to us as r(in km) * 106

friis formulates 3

In the same way, the frequency stays as F2 (in GHz) * 1018. It leaves a so great number because we have elevated the 9 of the Ghz to the squared one. The previous equation we have left:

frris 4

The previous expression, developing the quotient, is

friis 5 

The first term gives 92.44 us, which gives rise to the initial expression

Using this expression, to calculate the Db that must be obtained in a receiver, if the transmitter GHz with power of 2W being separated by 40 km operates to 6. The gain of 25 the transmitting antenna is of 20 dBi and the receiving one of dBi.

Zone of fresnel

 In order to avoid interferences being two points where one interchanges signals of high frequency, not only it is necessary to have cleared the reporting line between the emitters, but it is necessary to consider the zone of Fresnel.

zone of fresnel

It is possible to be shelp that the zone of Fresnel is the volume between emitter and receiver, where it does not have to exist obstacles that can disturb the transmission of the signal.

  In the Image superior one is the Ruptures of the zone of fresnel by passage of vehicles, low height of emitting-receiving or growth of plants.

 zone of fresnel

A formula exists that allows us to calculate if between two meeting points (although visibility exists), we have possibility of establishing communication. The calculation of the value of r (Distance from the horizontal of connection to the obstacle) comes given by:

 radio maximum zone fresnel

Where d1 and d2 are the distances that there are between the obstacle and emitter and obstacle and receiver As we can see, the form of the zone of fresnel is oval. This takes to us to think that the maximum we have it in the central zone, where d1 = d2. Of here, that stops the maximum distance we have the formula:

where f is the frequency given in Ghz and D is the distance given in km


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fresnel simplified 1

We have them distances are equal, and for that reason we are going to replace d1 = d2 = D/2, being distance D the value that we have between emitter and receiver. In addition we are going to replace the wavelength by the frequency so that λ = c/f Replacing in the formula we have:

fresnel simplified 2

If now we replaced c, we have:

The 106 are used next to another 103 uses that it comes from km to have 109 that. That is the reason for which the frequency that there is to put is GHz

Therefore, D comes in km and f in GHz.

Activity. To deduce the previous formula, knowing that the waves travel at the speed of the light and that the relation between the frequency and wavelength is c = ƒ*λ. Solution at the end of page

2,2 Systems of radio and television

One of the problems of the analogical television is the double image. It explains using a drawing, the reasons that cause it.

2.2.2 Systems of radio and television by satellite

DAB of car
Digital radio by satellite
DAB (Digital Audio Broadcasting). Of little implantation due to the price of the receivers, it offers characteristics as high quality of sound (CD) and unique frequency.

If in A.M. we have a rank of 540-1600 KHz, in FM 87,5-108 MHz and TDT of 470 - 790 MHz, in DAB the work frequencies is in the rank 1492 1592 MHZ

Systems of movable telephony

The movable telephony has evolved as much, that many of the systems have been obsolete already. In this section we will take care but thorough of the recent systems but. We will do one first

Speed of transmission

Activity 2. To calculate the time of unloading of a video that occupies 20 Megabyte using a 54 line GPRS of kb/s and the time using a HSPA of 14.4 Megabyte/s. To consider that the speeds usually occur in bits and the capacity of archives and data in byte and that a byte = 8 bits

2.4.2 Network architecture
  1. In order to contact between two movable devices (that in addition can move in the communication, if for example one of them goes in car). So that the process takes place with guarantees, the following elements are needed (software or hardware)
  2. VERSUS It is the station bases. When a terminal is in the cell of one VERSUS, that VERSUS is the one that controls the communication. The reach goes from some hundreds of meters to 30 km, following the surroundings (mountain, opened field, city, etc)
  3. BSC. It controls several Versus of the zone of influence. It coordinates the communications between the stations. It grants the frequency, power and position of the mobile to determine that Versus she is the suitable one for his communication. Perhaps a mobile is physically but near one VERSUS, but it has but signal of another one. In that case, the BSC changes it so that possible and greater quality of communication is used the smaller energy
  4. MSC. This system is in charge to contact, to maintain and to finalize from a user to another one. If one changes of cell, the BSC transmits the new position to him of cell to the MSC so that this one transmits it to the new ones VERSUS implied.
HLC and VLC. They are registries that are realised on the services contracted by a user and the position that it has then. If somebody calls to him, when registered being, the MSC can transfer the call to the suitable MSC. The VLC is own for roaming, so that when doing the consultation of the contracted service, will say if it has or privileges not to be able to use the services that it asks for.

Activity. Aside from the previous systems, within the device we have a series of codes. It explains what is and why they are worth  

Systems movable cellular deprived public and
Within the Private ones:
The necessity to contact with characteristics different from the public ones, produces the development of other systems that are used by security bodies, private companies, services of help, etc

The advantages that offer these systems are:

1º Communications of user to several users. Of this form, a worker speaks and several listen. This does not happen with the public one.

2º Can define a closed group of users.
3º Technology PTT (push to talk). If you beat you speak. If you stop beating, listening
We have two systems (PAMR, PMR and TETRA), each with specific features. We will emphasize the TETRA, that it offers some advantages as they are

  1. Destined to bodies of security, emergency and transport
  2. Use of digital modulation DQPSK (a variant of the QPSK)
  3. Ample cover thanks to the use of the devices as connection door. If a worker is in the border of cover of the main antenna, its device for of emitter communicating with other users who are outside the cover of the base
  4. Very stable system against incidences (more robust).
  5. It can work in terminal mode to terminal, in case of failure in the communications.
  6. Possibility of point-to-point calls, point to multi-point and between several users.
  7. Band of 400 MHz, that allows major reaches with respect to which they use majors frequencies.

  Great DevisesIf necessity exists to take a complete system TETRA to a distant point to the base, by means of movable systems, required time to do it operative small is compared with other systems


an electromagnetic wave loses energy due to ......

a coaxial cable with respect to a pair of copper has more or less lost. The answer on the basis of the diagram of the presentation reasons

What is the Skin effect. Help with three drawings

Tenemos in store two coaxial cable roll types. One of low other losses and normal. To that this is due? What element changes in the cable?

a fiber cable works with light of 850 nm.

a) To calculate that loss we have to 10 km if the length overall is of 60 km, the exit of the transmitter are 30 mW, the loss of the 4 connectors is of dB, the loss by joint is 0,15 dB, the joints are placed each 2 km and the loss of the fiber is of 0,35 dB/km.

b) To calculate the power in the receiver given in dBm

6º a coaxial cable is connected between the source (that provides 10 W) and loads and has a 1,5 loss of dB/100 M. Calcular the W that we have in a load located to 27 ms

  1. To show/To hide Solution
  2. We pass the 10 W to dBm.
  3. We make a rule of 3 to see whatever db are lost to the 27 meters: Lost of cable 2 . Of this we have
  4. We clear that attenuation (40 - 0,405 = 39,595 db)
  5. Now we calculated the power that arrives to him, so that: expression

We elevate to the power of 10 to clear lg =>

In a tower we have a generator of 20W to feed an antenna that is to 40 meters. If the cable has lost of 2dB/100 meters, that power arrives to him at the antenna.

   To calculate the power that we have when coming out of the receiving antenna whose directive gain has value of a 5 and one efficiency of 80%, located to a distance of 20Km of the transmitting antenna of directive gain 4 with efficiency of 70% that receives a power of entrance of 40W. The work frequency is of 150MHz.

solution problem friss

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Busca in Internet what models of cars have the DAB

10º the compass is a simple and very useful instrument for our work. In addition, smartphone already has one including. a) Opens the compass and looks for the direction of a point anyone of your surroundings. It compares the result with your companion b) Looks for facilitated the North and South coordinates. It compares these values with facilitated by google maps. It compares results both. Then, Raisin the values of the compass to the data of google maps to see that result offers to you. You in account that one comes in the decimal system and the other in minutes and seconds. PS. In the map of google, we have a positive value in the coordinate that indicates the degrees that are on the Equator and another negative, because we are before the meridian of Greenwich

11º Optative Work.  Project of Computer science. It realises in php an application to calculate the zones of fresnell taking as variables from entrance the distance from bay to bay, the distance of the emitter (left) to the obstacle and the transmission frequency. The work must be in a webpage and being responsive (adaptable to mobiles). Working time: 1 week. (to see example in

Projects of radio link:

We will first see a video on Radio link

Part 1º. (I have left to a pdf in DRIVE with the title Calculation De Radioenlace where radio link examples are exposed)

The idea of this first practical one is to realise a radio link from two points to choose of your surroundings, with real components. For the characteristic of the station it bases, that feeds the antenna, I have left a document pdf in the shared folder of DRIVE.

 Rocket can be looked for in Internet as ubiquiti m5 datasheet.

  1. We enter the application online of Radio Mobile (
  2. First that we must do it is to come with the registry to be able to create connections
  3. Within the application, we found the section Cover. This section is used for knowing to us what cover has the antenna that we are going to use, with the height that we give him and its frequency of work. It is very important to let it first of all to know what zones are susceptible to make a direct radio link. I have realised a screenshot of a located point in the is Mare Nostrum and the result has been this:cover Malaga antennaThe zones in green offer a high power and the yellow to me an average signal. If there is no color, it says to me that in that zone there is no cover. To fix to you that zones near of the center do not have cover (by the near buildings) but in distant and high zones but (limonar).
  4. Once we entered, we created a new location and, in our case we located the cursor in a point of Islantilla
  5. We give name to that point and we created 2º. In this case, he is the shopping mall where an omnidirectional antenna exists to give service to the clientsRadio mobile online
  6. Once we have points of the connection both, we created a new connection where are the different parameters to consider (shown in image)
  7. a) Height of the antenna talks about from the ground, therefore, first we have it to 10 meters and 2º to 15 meters. We have used a frequency of work of 2,3Ghz with an emitter of 1 watt, with some losses between the emitter and 3 antenna of dBi (indicated by loss of Tx line). The transmitting antenna Tx has 15 Dbi of gain and the receiving Rx of 2. The Rx loss of cables and connectors in the 2 reception is dB and the receiving antenna has a sensitivity of 0.5 microvolts, or what is equal, of -113,03 dBm. The reliability we put it to 70% to make sure an allowable errorRadio mobile online 1
  8. With all those data, we give to send and to the few seconds a map with the data of performace is created, that we showed next
  9. Radio mobile online 2In the first image we see that houses exist a series of obstacles (before arriving at destinyRadio mobile online 3
  10. In the table of results we have casa20 as origin of the signal and where we want to receive the data. Nothing new exists and the given data are only reflected at the outset. We happen to see that data we have in destiny Radio mobile online 4
  11. The first part talks about to geographic data and the second the losses that we have. The first and most important one is the created ones in free space. We must add all the losses that the 94.45 system gives us and have are dB as total losseses. We will see performace now (result)
  12. It accurately says that there are 319 meters between the two antennas, to + - 10 meters to us to a frequency of 2300 Mh and one gain of the 156,52 system of db. Deserts in this first point to see where it leaves.
  13. The gain of the system will be the sum of the gain that it transmits, clearing lost and taking into account the threshold sensitivity. That is to say, we have 30 - 3 +15+2-0.5+113.02 = 156,52 dB. This S-value greater as Rx sensitivity is greater, the greater power and the smaller losses
  14. We follow with the previous table and it indicates to us that there is a received signal of 50.95. This comes to remain to the emission gain, the losses of transmission, that is to say, we must operate as 30 - 3 +15+2-0,5 - 94,45 = - 50,95 dB

The listening margin obtains when remaining the total gain and total losses (156,52 - 94,45) = 62,07 dB

2º Part. To carry out the same task, with the same points of work and equipment, using the program of Another page with tools to calculate the zone of fresnell: 

3º Practical (voluntary)

Also we have the possibility of installing the radio tools mobile in our PC. For it, I leave documentation that is in the following connection

To show/To hide to Practice Installation Mobile Radio

Part 2.

Installation of the complete program in the PC.  First of all, we have these videos of a colleague of Venezuela:

1º Part

2º Part


1º Ir to the Web to make a registry of user. To puncture in Radio mobile online to make a registry online and to work on the program already lodged in a servant

 2º If we want to install it, (we will do it) we must follow the guide indicated in the section download

3º Tenemos to choose two points now anyone. That they are not much to avoid the terrestrial curvature.

 4º Hacemos 1º measurement and in the results we have a sample of the zones of fresnell, reporting line (in red) and the data of the transmission and reception calculation gain radio link

The significant values but are those that we have put) (These data are the characteristics of equi In the transmitter: tx is the power transmitted by the system in dbm. The power of dbi is obtained developing this process:

Where x is the power in dBm (decibels in. To see page and to verify as it evolves dbm from his maximum value to the minimum. Rx occurs in dbi, that is gain with respect to the isotropic antenna.




Rx sensitivity makes reference to the minimum level of signal that is needed for a correct operation of the equipment. In the right part we have the data regarding the lost one by the propagation In performace indicates the results given the orographic and technical characteristics to us

Design PCB