Channel amplifier - why and when to use it?
It would seem that building an antenna system, reliable and stable for many years of operation, is very simple. Just buy an antenna and connect it to the receiver with an appropriate cable. Nothing could be further from the truth! Though there are certainly happy exceptions.
The main challenge in building and starting up an antenna system is significant difference in signal levels between individual frequencies (channels). In small systems it may not matter much, due to short distances from the antenna to the receiver and small number of outlets. However, in more extensive RTV/SAT networks the differences in signal levels are crucial for proper operation of the whole system.
Where do the differences in signal levels come from?
The primary reason for the disparity in signal levels for different channels is the non-uniform attenuation of individual frequencies in different environments, e.g. air, cable, etc. These differences increase with increasing distance and frequency. Other causes causing differences in signal levels include:
- parameters of transmitters that broadcast particular frequencies (MUXes) with different power;
- reception of signals from several transmitters and different directions;
- antennas with different energy gain (different power at the output of the antennas).
Bearing in mind all the factors mentioned above, it is not difficult to see that every system is more or less exposed to the disparity of signal levels. The real trouble comes when these differences become significant. Large discrepancies have a key impact on the correct and stable functioning of the network as a whole receiving system. Therefore, the regulation of the Ministry of Transport and Infrastructure stipulates that the maximum difference in signal levels within the whole DVB-T band in a community antenna system cannot exceed 12 dB. So any system for DVB-T reception should be properly balanced. This means that all signal levels that are received and are to be used for further distribution should be pre-aligned even before they are summed. Then amplify or lower the level of the overall signal/band as appropriate for your system.
Channel amplifier to the rescue
The ideal solution for ensuring proper signal processing before further distribution is the use of channel amplifiers. Their design allows to isolate individual frequencies (channels), properly equalize their power, and then sum up. These amplifiers have several independent band inputs that allow to connect several antennas at the same time. This allows us to tune and adjust each one accordingly. The signals thus selectively equalized and adjusted are then summed and, if necessary, amplified to the desired level, depending on the needs of the particular system. Only such ordered signals can be properly distributed without fear that inter-channel interference may occur. Such a procedure is especially important when the individual MUXes (channels) are broadcast border to border, i.e. in close proximity to each other. This increases the danger of frequency overlap - interference and thus generates errors and disturbance. Already now there are areas where transmitters broadcast individual MUXes on adjacent channels. And in the near future, we will be forced to make a dividend allocation for DVB-T bypassing channels 50-59. So it's going to get even tighter.
Channel amplifier - which one to choose?
We have several types of channel amplifiers to choose from, so we can select the right kind for the specific needs of each system. For smaller systems we recommend WK range amplifiers, for larger ones - WWK range.
WK-410 channel amplifiers allow us to select four signals of different levels received only in UHF band (two inputs with two UHF filters each). In addition, they have an unregulated input for VHF and UKF (FM) bands, which are summed up with the already equalized UHF signals. So they work as a branching filter allowing an additional adjustment of signals from UHF band. Due to relatively low signal output level, the WK-410 amplifiers are recommended for less extensive systems. If there is a need to supply more outlets in the installation, the WSS-1138 amplifier can be additionally used as a second stage amplifier.
Multiband channel amplifiers from the WWK range are a generation of devices whose advanced design allows application in locations with difficult reception conditions, where signals of different levels are transmitted from several directions. The amplifiers of this series allow us to receive these signals, equalize their levels and amplify them.Depending on the model, it is possible to connect up to 6 different antennas from different bands (UHF, VHF, DAB, UKF/FM) and to select and independently adjust up to 11 acquired signals (channels). The WWK amplifiers can be used individually in antenna installations for receiving digital terrestrial television broadcasts (DVB-T) in one-family houses, hotels, boardinghouses, recreation centres, schools, hospitals, or as part of a large multiswitch system.