At the beginning of summer 2019, analogue television broadcasting was completely stopped in Russia. Now, to continue watching TV, you need to:
- purchase a new TV capable of receiving digital signals, or
- install a DVB-T2 set-top box, which converts the signal arriving at its input into the format for which the previous generation television receivers are designed.
It often happens that the common house antenna fails and the reception of TV programs stops. Especially elderly people suffer from this, who no longer leave their homes and for whom television is becoming the only window into the world.
Independence from the state of the common antenna is provided by a purchased or home-made indoor antenna, Figure 1. The manufacture of a high-quality home-made antenna is not within the power of every person, even with a specialized education. Therefore, in the future we will proceed from the availability of a purchased product, Figure 1.
Feature of receiving digital TV signal
One of the main parameters that determine the quality of functioning of any radio technical device (TV, cell phone, radio) is the signal-to-noise ratio at its input. The signal strength must exceed the noise power at least a certain number of times. If this condition is violated, a so-called "Snow", and with the new digital - strong distortions of the image begin and it "stops" playback.
A digital system compares favorably with an analog system in that it continues to function normally with a noticeably lower signal-to-noise ratio. This is achieved due to the fact that information about the reproduced image is encrypted by the fact of the presence or absence of a pulse signal at a specific moment in time, which is schematically illustrated in the figure 2.
The latter is determined by comparing it with the so-called response threshold of the solver, which is one of the mandatory blocks of a digital receiver. The noise that is inevitably present at the input of the receiver does not exceed the threshold in normal TV operation triggering, which is set at half the amplitude of the digital signal, and image distortion is not going on.
Sources of the problem and how to fix it
The noise power at the receiver input is constant, and the signal power depends on a number of factors. In unfavorable conditions, it is insufficient and then we get the picture, which is shown in Figure 3. In this situation, the receiver is not able to correctly recognize the zeros and ones of the digital signal and the image quality is at least drastically degraded.
You can restore the normal operation of the TV by correctly setting the antenna and using an amplifier. The methods are independent and, if necessary, are applied together.
Antenna tuning
In this case, tuning the antenna means choosing the correct choice of the installation site and setting the orientation. The need to choose the correct installation site is due to the fact that there may be “dead zones” within the premises due to the architectural features of the building. The signal strength increases in the area of \ u200b \ u200bthe windows, often varies greatly in different rooms due to the shading of the radio signal by nearby standing buildings, etc.
The orientation is selected due to the fact that the indoor antenna has a certain directional pattern, i.e. the dependence of the gain on the angle of rotation, Figure 4. As a result, when it is rotated around the vertical axis, the reception quality can be significantly improved.
Amplifier application
Application antenna amplifier, one of the variants of which is shown in Fig. 5 is justified in the event that it is not possible to obtain a high-quality image using the antenna tuning. Some TVs show the received signal strength in manual or auto tuning mode. If the readings of the level indicator do not exceed 50%, then the use of an additional amplifier becomes, if not mandatory, then highly desirable.
When using a standard indoor antenna cable, due to its short length, the place where the additional amplifier is turned on does not matter. If the antenna cable has to be extended, then the amplifier is turned on as close as possible to the antenna output, Figure 6.
Important! When using a DVB-T2 set-top box, the amplifier must be located between the antenna and the TV input.
Setting process
Using an indoor antenna will most likely require some tuning. It starts with choosing the right antenna location and setting the orientation. If the received signal strength is too low, an additional amplifier must be installed.
These procedures are not very complex and for their implementation there is enough accuracy, reading the instructions on the TV and the level of knowledge of the secondary school.