Cable TV networks for the little ones. Part 6: RF signal amplifiers / Sudo Null IT News

Jul 2018

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Setting up television antennas at home is usually done using receiving and reproducing household equipment located in an apartment or house. The presence of a receiver and a TV in this case is sufficient to determine the signal level and correct it. We are, of course, talking about a primitive coordination of the elements of the chain, which includes an antenna, cable and television receiving equipment. For deeper settings, specialists use professional measuring instruments, which can greatly reduce the time of such work and simplify their implementation. The use of such devices makes it possible to determine the signal level in a matter of minutes and adjust the receiving antenna in accordance with the passport parameters of the receiving household appliance.

Checking the TV signal without a TV

The technique for measuring the level of a television signal without using household appliances consists of connecting the appropriate equipment to the circuit between the antenna and the receiver, or directly to the antenna cable. Using this method, the measuring device records the level of the input signal, and the specialist determines its parameters. In accordance with the results obtained, the built-in receiving unit of the TV or a separately connected receiver is configured. In this case, the specialist can only correctly orient the receiving antenna and coordinate its parameters with the passport characteristics of the receiving equipment. Usually the antenna is directed in such a way as to obtain the maximum level of the TV signal.

Modern devices for tuning standard and satellite antennas are now available in a very wide range. These include:

TV signal level meters with dial or digital indication;
devices with a built-in compass that determines the position of the satellite;
devices with their own software and the ability to enter additional settings;
spectrum analyzers used for finer and more precise tuning of receiving equipment;
universal analyzers operating in TV receiver mode with support for various image formats.

The choice of the type of measuring equipment directly depends on the type of antenna and the tasks assigned to the specialist.

Advice from professionals

During the assembly and installation of the signal amplifier, it is necessary to take into account not only the recommendations of the manufacturers, but also follow the advice of professionals. They will help you avoid most simple mistakes and achieve the desired result in a minimum amount of time.

Key recommendations from experts:

The antenna amplifier must be located in close proximity to the TV. This is done in order to reduce cable losses, which can cause deterioration in the quality of the television picture.
It is not recommended to equip indoor antennas with signal amplifiers, as this will not provide any benefits and will not eliminate interference.
Before using the device, be sure to study the included instructions in detail. This information will help you install the device correctly and reduce the likelihood of installation errors.
If the installed amplifier does not solve the problem, then the cause of poor signal quality should be sought in the antenna itself, its location and correspondence to wave frequencies.
Any installation, repair or maintenance work on the device should be carried out only after it has been disconnected from the power source. There is a high risk of electric shock.
It is prohibited to connect the signal amplifier to antennas located on the roof of a building or in rooms not equipped with lightning protection. If you neglect this advice, you may lose not only the amplifier, but also the TV.
Do not connect a device that has visible damage to the housing, as this will increase the risk of electric shock.

A TV signal amplifier is a useful and inexpensive device. With its help, you can eliminate various interference and significantly improve the quality of the television picture. With the right approach to choosing a device and following all the recommendations of professionals, you can achieve the desired result and reduce the likelihood of malfunctions.

TV signal level according to GOST

The TV signal level is measured in decibels (dB), taken in relation to the effective voltage (1 µV). The designation looks like this: “dBµV”. In accordance with existing GOST, the value of this parameter should be in the range from 60 to 78 dBµV (these indicators are focused on a package that includes more than twenty programs). The optimal level of a television signal, at which the input signal-to-noise ratio has acceptable values (26 dB), is an indicator of the sensitivity of the television receiver. This parameter is specified in the device passport. Modern TV receivers are designed for a minimum input signal:

32 dBmV in the meter range;
37 dBmV in the UHF range.

Taking into account the fact that acceptable image quality is observed only at a signal level value that exceeds the receiver sensitivity rating by 20 dB, this value at the input of the receiving equipment should vary in the range of 52-57 dBmV.

In addition to this indicator, the signal characteristics are seriously influenced by such parameters as the ratio of signal to noise levels, as well as the level of intermodulation (nonlinear) distortion. Typically, such complex measurements are not carried out by specialists, but, nevertheless, the quality of the image largely depends on them.

According to existing standards (GOST [2.3]), the value of these parameters should not exceed:

-72 dB/mW (70 µV) for meter range;
-69 dB/mW (100 µV) for the UHF range.

The sensitivity of an individual video channel, taking into account the limitations associated with synchronization, directly depends on the minimum signal amplitude at the input of the television receiver, which ensures stable image synchronization. The meaning of these parameters is as follows:

in the meter range it is acceptable within -75 dB/mW (40 µV);
in decimeter - should not exceed -72 dB/mW (70 µV).

What determines the quality of TV broadcasting?

There are several factors that influence the quality of the transmitted image:

The television receiver is located at a great distance from the signal repeater.
The presence of external obstacles, both natural and artificial. These can be the walls of high-rise buildings, hills, lowlands and a large number of trees.
Poor quality connecting cable.
The antenna is installed in the wrong location or is poorly oriented in space.
The presence of significant metal structures in the signal path or in the immediate vicinity of a television tower.

In almost each of the listed cases, the leading role is given to the TV antenna. If this attribute is correctly selected and configured accordingly, then there is a real chance of improving the quality of received signals and stabilizing the broadcast.

The industry produces both indoor and outdoor antennas. Where they are installed is clear from their name. Let's look at each type in more detail.

Measuring a TV signal using a multimeter

A multimeter is a universal measuring device that can be used to measure voltage, current, resistance, capacitance, inductance, and also carry out cable testing. Some types of stationary devices of this type are equipped with a frequency measurement unit. I would like to immediately note that it is impossible to measure the level of a TV signal with a conventional multimeter. If the device has a built-in frequency meter, it becomes possible, when setting up a specific channel, to check the correspondence of the specified value and the actual indicator of this parameter when setting up the antenna. Basically, a multimeter is used to measure the resistance of an antenna cable and check its integrity.

How to check an antenna with a tester (multimeter)

First of all, you should pay attention to the TV cable. It should be intact and without any crimps.

If this is a multi-story building, then you will only have to check the functionality of one end of the cable (with a plug). For this, a multimeter (tester) is used to measure the resistance between the braid and the central core of the wire. A value of several tens of ohms is considered a normal value. If it is greater than or close to “0”, a break or short circuit has occurred. In this case, it is better to find out whether the neighbors have a signal and, if so, then the problem is in the junction box or in the area from it to the plug.
If this is a private home, then you can check the resistance of both ends of the TV cable. First you need to unplug all equipment from the outlet. Then disconnect the wire from the antenna and from the TV. And in the same way, use a tester to check the braiding and the central core for short circuits. Here, the serviceability of the cable is indicated by an infinite resistance value. But, if you short-circuit the central core and braid, the multimeter should show a value close to “0”.

When the device detects a malfunction, it is necessary, first, to find the weak point of the cable. This usually occurs in places where there are sharp bends, connected sections, or where the wind sways. If everything is fine with the TV cable, the cause of the problem should be looked for elsewhere.

Measuring TV signal in SCTV

To measure the basic characteristics of a television signal in a cable TV network (cable television network system or SCS cable network system), you will need a signal generator, a spectrum analyzer and a digital oscilloscope.

These measurements include:

Impulse noise level. It is carried out by the method of accumulating sweeps, from the characteristics of which, using special software, such characteristics of the output signal as the width and amplitude of the pulses, as well as their periodicity, are calculated. Such measurements are carried out in conjunction with recording the level of total interference. The scan should be recorded at intervals of 2-8 seconds;
Total interference level. Such measurements are performed using a spectrum analyzer by recording spectral analysis data of the interference, and are carried out at intervals of 8-10 seconds. Testing is carried out over eight hours. In this case, the bandwidth of the device is set:
at intermediate frequency at 30 kHz;
via video at 10 kHz;
the detector is switched to peak mode.

Using the appropriate software, the spectral power is adjusted and the ratio of the signal power level and the total interference for a single channel is determined;

Determination of the frequency response of the path. The determination of these characteristics is based on the method of analyzing the distortions of a test signal of a certain shape, supplied by a pulse generator to the input of the path. To perform such measurements, the following equipment is required:
Pulse generator used as a source of the tested signal;
digital high-frequency oscilloscope (with a bandwidth of up to 50 MHz), equipped with an interface for transmitting received information;
a device for storing the obtained results connected to an oscilloscope.

The resistance at the input and output of the devices used must correspond to the indicator - 75 Ohms.

How to check an antenna with a tester (multimeter)

First of all, you should pay attention to the TV cable. It should be intact and without any crimps.

If this is a multi-story building, then you will only have to check the functionality of one end of the cable (with a plug). For this, a multimeter (tester) is used to measure the resistance between the braid and the central core of the wire. A value of several tens of ohms is considered a normal value. If it is greater than or close to “0”, a break or short circuit has occurred. In this case, it is better to find out whether the neighbors have a signal and, if so, then the problem is in the junction box or in the area from it to the plug.
If this is a private home, then you can check the resistance of both ends of the TV cable. First you need to unplug all equipment from the outlet. Then disconnect the wire from the antenna and from the TV. And in the same way, use a tester to check the braiding and the central core for short circuits. Here, the serviceability of the cable is indicated by an infinite resistance value. But, if you short-circuit the central core and braid, the multimeter should show a value close to “0”.

Measuring a TV signal in an optical cable

The main element of fiber optic networks is the fiber located inside the optical cable. To maintain and test such systems, specialized measuring equipment is required. Here are some devices without which it is impossible to perform any measurements on optical lines:

optical reflectometer (OTDR) – makes it possible to determine not only the level of losses in the system, but also the location of damage to the optical cable;
optical tester - presented in the form of an independent radiation source and a device for measuring optical signal power;
optical power meter – records the signal level indicator and displays its numerical value on its screen in Watts or dBm. The main measuring element of the device is a photodetector.
flaw detector – causes a red glow on damaged sections of the optical cable;
active fiber identifier – the device is designed for a quick, gentle (non-destructive cable integrity) method for determining the presence of a signal and its direction in an optical fiber. It makes it possible to detect the presence of a signal without turning off the transmitting and receiving equipment, as well as determine its strength and direction.

Let's figure out what characteristics of fiber-optic communications we are talking about when servicing and repairing them. The first indicator that experts pay attention to is the level of attenuation of the optical signal at a certain wavelength (measured in dB). This value characterizes the quality of the fiber optic cable and the level of installation work performed during its installation. The main elements of the system that cause this process to occur are:

optical fiber (losses are measured in dB per unit distance);
welding connections;
connectors;
connectors;
dividers, etc.

The next important characteristic for optical communications is back reflection. This value determines the power of the signal reflected to its source and is also expressed in dB. The main reasons for the occurrence of a reflected signal, as a rule, are mechanical damage to the optical cable (cracks), the presence of mechanical connectors, or a cable break at the connection point (free end).

The use of the above devices allows a specialist to achieve the output signal to the required level and ensure reliable operation of the receiving equipment located in the apartment or house. So, if you have problems with the image in SCTV conditions, you should contact the operator who provides these services to you.

How to check the head (converter) of a satellite dish

The most common problem with satellite devices is the failure of the antenna head (LNB) or DISEQC (switch). This is usually understandable if some TV channels suddenly stop showing. The converter can fail due to precipitation, short circuit and sudden voltage surges.

To check whether this problem is actually due to a converter or disk failure, you must:

Turn on a channel that has stopped working.
Unscrew the LNB head from the cable.
Disconnect the center wire from the receiver and connect to the LNB.
If in this situation the channel begins to show, then the disk (switch) is faulty. Otherwise the converter is broken.

But, if there is no connection even when replacing the LNB head, then you should look for the reason in the equipment settings.

How to check your satellite dish receiver

Before you begin your next attempt to test the antenna, it is best to try the previous steps again. Perhaps there was a mistake made somewhere. If nothing helps, you can check the receiver for serviceability.

First, you should go into manual settings and write down the parameters for the satellite of this provider.
Then, take the device and connect it to another satellite TV.
After that, select manual search in the menu, where to find the desired satellite and set the already recorded parameters.
If both scales are colored and have a numerical value, then the receiver is working properly, otherwise it will have to be sent in for repair.

In any case, you should not immediately rush out and buy a faulty element or call a repairman. It is better to try to go through each point of checking the television antenna 2-3 times. And only then can we draw any conclusions.

How to check the head (converter) of a satellite dish

To check whether this problem is actually due to a converter or disk failure, you must:

Turn on a channel that has stopped working.
Unscrew the LNB head from the cable.
Disconnect the center wire from the receiver and connect to the LNB.
If in this situation the channel begins to show, then the disk (switch) is faulty. Otherwise the converter is broken.

But, if there is no connection even when replacing the LNB head, then you should look for the reason in the equipment settings.