DIPOL para a educação - Sistemas SMATV e CCTV
O artigo apresenta as propostas que constroem exame está em escolas técnicas / profissionais. Além disso, ele enumera outros artigos que podem ajudar a compreender algumas questões práticas relacionadas com a eletrónica.
Locais e os parâmetros de analógica terrestre e transmissores de TV digital na Polónia
Locais e os parâmetros de analógica terrestre e transmissores de TV digital na Polónia (Informação adequadas para usuários de língua polaca apenas)
Symbols used in diagrams of antenna installations (Polish norm)
Symbols used in block and wiring diagrams of community antenna installations in Poland (information suitable for Polish users only)
Planejamento da Instalação - individual e sistemas de antena comunidade
condições e requisitos específicos, conceito, design, desenvolvimento futuro, cabeamento.
Basics of designing MATV/community antenna systems
Community antenna (MATV system) may be defined as antenna installation where compensation of network attenuation is performed by one (central) set of amplifiers. The amplifiers can be connected in a cascade.
Antenna signal measurements
Most of parameters can be measured using selective signal level meters. Performing such measurements is not a waste of time but essential stage for proper design, and, the next - even more important - of verification of the work done. The measurements allow to verify correctness of the design and its implementation, as well as quickly find the errors arising both at concept and realization stages.
Theory and use of channel amplifiers
A common problem that is encountered in terrestrial TV antenna installations is unbalance of the level of received channels, often about 10-20 dB. In case of small installations (5-20 outlets) such a difference (not recommended) usually doesn't make any trouble yet. It is the real problem for bigger installations, where the difference of levels at the input is increased by inconstant (being a function of frequency) attenuation of cables and may easily exceed (in an outlet) the accepted limit (12 dB) all over the band.
Distribution of digital signals in cable TV systems
QAM modulation is optimal for cable networks. It is used in cable band/hyper-band (S channels) and UHF band. Due to the need of compatibility with channel raster and transmission requirements, there are used 8 MHz channels (MPEG-2 compression, QAM modulation).
Maximum output level in active elements of community and cable networks
One of the important parameters of amplifiers is their maximum output level. It is the level which can appear in the amplifier output without exceeding an acceptable level of nonlinear or crossover distortions.
Digital satellite broadcasts
Thanks to digital technology, satellite industry has increased the number of channels that are broadcast from one transponder - there may be transmitted 5, 8, or even more TV programs. It lowers operating costs and makes possible to multiply the offer from a single satellite. The important factor is compression level that can be changed according to the intended quality of the image.
Electromagnetic compatibility (EMC)
RF cable network should fulfill regulations of electromagnetic shielding. It cannot radiate energy that exceeds determined level and it should be resistant enough to outer electromagnetic radiation.
Splitters and taps
To ensure proper S/N ratio, the isolation between any two receivers should be at least 50 dB.When the receivers are connected to the same tap, the isolation depends on the Ao, A, and As attenuation, and the lengths of the cable between tap outputs and subscriber outlets.
Compression of video and audio signals
MPEG-4 is the newest video compression standard which quickly becomes popular, also in the case of video streaming. In comparison with previously presented standards, it integrates effective methods for multimedia data.
Separation between outputs of splitters
Separation between outputs of splitters (crosstalk attenuation) is very important parameter of the devices. It determines level of interferences coming from other branches of the network connected to the splitter. It should be as high as possible.
Filters in TV antenna installations
An ideal band-stop filter has no attenuation in the pass-band, 90-degree steep slope, and infinitely high attenuation in rejection band.
Canais TV (PAL BG/DK)
Canais de TV utilizados em Portugal e alguns outros países europeus para terrestre e TV a cabo de transmissão. Na Polónia há é usado PAL DK padrão, com contínuo de numeração (por exemplo, após S8 temos S9). Nós também apresentaram canais PAL BG utilizados principalmente em países da Europa Ocidental.
Conversion Table - dBuV to uV/mV
In the table there is comparison of signal level and corresponding voltage.
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