Measuring equipment in Telecommunications
Oscilloscope
It is an instrument that already it must to us be very familiar, like polímetro.
Since we have worked already doing practical, I am the connection for its review. To see Oscilloscope
Measurer of field
We see this measuring instrument in the Practical connection with the field measurer
Spectrum analyzer
It is a measuring instrument used by the technicians to realise diverse spectral analyses, with the idea to discover problems or to improve the transmission of signals. This is almost impossible task for an oscilloscope.
The analyzing word talks about to take something (a signal) and to disturb it in several simple parts.
The spectral analysis of a signal is bound with the mathematics of the transformed call of Fourier. By this one transformed, a spectral decomposition becomes of the components of an electrical wave and in addition, thanks to the inverse transformed one of Fourier, the original signal can be obtained.
On the other hand, the mathematical one of Fourier facilitates the phase to us of each component and therefore, each overtone can be represented by a bidimensional vector or as a complex number. Normally in the graphical representations the module only imagines the squared one of that number. The graph that is obtained power phantom of power is known as spectral density or.
Possible applications can be the one to measure the frequency response of amplifiers, to fit to the radiation frequency of a radio control control, to see the answer of filters, to analyze the Wifi signal, 3G,…
Basic functions of an analyzer
1º initial Frequency. A value adjusts so that equipment begins its analysis to that frequency
2º final Frequency. Just as the previous one, used to fit the last frequency of analysis
3º central Frequency is the value that adjust to show and center of graphic
4º SPAN is the value of the width of the window.
5º Amplitude: Value of each division of the screen given in dBm/division. If the signal is very weak, it is possible to be increased using a suitable preamplifier.
6º Filtro of resolution: it is a filter that happens through all the selected frequencies of the signal in the selector of Frequency. According to we fit this value, varies the precision, so that to smaller, greater resolution of the measurement and more time in processing.
7º Marking/Search of tip: It shows to the value of power and frequency to us of the signal in a concrete point.
In the following image is the basic equipment to analyze a signal (in this case GSM) to verify its parameters
Tellurometer
The Tellurometer is designing to verify the quality of the earthing.
It is totally necessary in facilities as houses, determined installation of antennas, systems of radio link, lightning rods, etc
This made up of:
a) Measuring equipment
b) Mattocks
c) Cables of colors and different lengths
At the time of verifying that a goad (the one that we want to measure) has a good earth, the Earth installation becomes disconnected and it is come to connect the green cable to the goad to verify. Later other two mattocks get ready in line straight and to a distance of 25 and 15 meters (to see image).
In the image of the installation is to + - 1 meter. This represents the allowable error that we have
It is necessary to emphasize that the measures where they go located the goads of the test are orientativas and we always must do what indicates the manual to us of the manufacturer
IT NIBBLES
Before seeing this parameter and its measurement, we will see that they are the standing waves, reflected and emitted
As a result of an evil design of the lines of communication, the original waves (emitted by the equipment) can have reflections in the same (Reflected wave) giving rise to a new wave, the Standing wave
A measurer of NIBBLES is an essential measuring instrument for a radio technician, unless other radio equipment bring one built-in one.
IT NIBBLES (Relation of Standing wave) is a value that obtains when considering the maximum and minimum values of the tension within a line transmission. In English SWR is denominated.
In order to understand it, we must consider the existence of a reflected wave within the line. That signal reflected (Vr) in its return to the source, is reconciled to the incident signal (VI) giving maximum and minimum values.
IT NIBBLES is defined as the relation between both extreme values
This expression also usually is put as
where
If the reflected wave is zero, we do not have maximums or minimums, with a signal of constant amplitude and a ROE=1.
If reflected wave exists, we will have maximum voltages and minimum, giving rise to IT NIBBLES >1.
Therefore, in an installation of telecommunications, to minor IT NIBBLES, better answer of the system
To speak of NIBBLES is to speak of its relative supply line and impedance matching of an antenna.
IT NIBBLES under mean a greater impedance matching between transmitter and antenna. IT NIBBLES of 1:1 means a perfect adaptation between equipment and antenna, which does not guarantee that the antenna will emit all the energy of Radio frequency that the transmitter sends to him.
As the transmitted and reflected tension has an equivalent to transmitted and reflected power (for a certain impedance of line), the previous expression can be left as:
An equipment transmits 20 W and 1 W is given back. To calculate the value of NIBBLES. Solution: 1.576
How it is made?
Very simple. We show an analogical equipment used in teams of radio hams where equipment has two needles indicating the incident and reflected power. The connection is simple, with one to the equipment and another one to the antenna.
We show a graph so that you verify the value of NIBBLES of the previous exercise.
If we needed to know the behavior of a joint equipment-line for a certain rank, graphs of the type are obtained.
In the graph, the behavior in rank 880 is obtained -960 MHz
The value in vertical axis comes in VSWR, doing reference to the value in tension.
Pressure gauges
Certain facilities use waveguides instead of coaxial cable. Usually they are facilities of great power where it is important to have low losses.
The waveguides are appropriate for this, but to avoid alterations in the signals, the tube must have the smaller possible air (we remember that the air contains aqueous vapour and the aqueous vapour is not good friend of the waves).
For such intention vacuum pumps are used and to verify that we do not have lost, usually it is had pressure gauges connected in the installation.
- The used units of pressure more are
- The Pascal, as fundamental unit that he is equivalent to 1Nw/m ²
- The atmosphere
The bar. Also we can express the bars in Kgf/cm2 The atmosphere and the bar are almost equivalent. The pascal is equivalent a 10−5
bar.
We measure the pressure of a tire and it gives to a question reading 2.25 bars us. To pass this value to Pascales. Sun: 225 kPa
Thermometers