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TV & SAT TV

Sobre Antenas TV & SAT

Seleção de Antenas de TV terrestre
Versão real do artigo pode ser encontrado sob este endereço www.dipol.com.pl/bib217.htm
Este pequeno guia foi elaborado para aqueles que gostariam de realizar / substituir a antena de instalação por conta própria e vivem em áreas com condições de uma boa recepção.
No caso de sinais de baixa, as reflexões, as interferências - que aconselham a chamada experiência de instalação da antena, que conhece bem as condições locais.

A seguir, analisar os fatores que devem ser levados em consideração na escolha de antenas de recepção.
Não podemos garantir que este conselho irá garantir resultados satisfatórios em todos os casos.
Factores que determinam a seleção de antenas
1. Distância do transmissor / transmissores
2. Número de transmissores e bandas de freqüência seus
3. Distâncias angulares entre os transmissores
4. Potência de saída dos transmissores
5. Diretividade de antenas transmissores
6. Polarizações dos sinais transmitidos
7. Obstáculos entre transmissão e recepção de antena
8. Tipo de instalação
9. Influência de interferências, incluindo sinais indesejados de outros transmissores.
1. Distância do transmissor / transmissores é o principal parâmetro que tem que ser tomado em conta na escolha da antena. Para antenas longas distâncias têm de assegurar ganhos mais elevados.

 

Até 10km

Até 25km

Mais 25km

Broadband antenna (planar)

SIM

NÃO

NÃO

Logarithmic broadband antenna A4011

SIM

SIM

NÃO

Set A0710 +A1910 (Yagi)

SIM

SIM

SIM

Set A1116+A2682 or A3710 (Yagi)

Desnecessário

SIM

 
SIM
Selecção de antenas em relação à distância entre o transmissor
Quando a distância for superior a 20 km, a escolha adequada é o conjunto A1116 + A2682 ou A3710, com preamplifiers - por exemplo, B4033.
2. Número de transmissores (locais diferentes) A situação em que todos os sinais são transmitidos a partir de um único local é bastante raro (algumas cidades) - na maior parte dos casos, têm de receber sinais a partir de duas ou mais direcções. Portanto, temos de empregar um número de antenas direcionais. As antenas de banda larga (construções planares) não são adequadas para o efeito, devido ao ângulo de meia potência de largura (cerca de 45 graus), o que iria afectar a interferência de sinais.
Exemplo 1
Bochnia, entre Cracóvia e Tarnow: há dois locais de transmissores: Choragwica (Cracóvia), Gora Sw. Marcina (Tarnow)

TV program

TVP1

TVP2

Polsat

TVN

TV4

Puls

TVP3

Channels (transmitter Choragwica)

10

33

53

30

35

27

50

Power

high

200kW

high

300kW

high

100kW

medium

10kW

medium

10kW

medium

10kW

high

200kW

PolarizationHH
H
H
H
H
H
Transm. antenna
omnidirect.
omnidirect.omnidirect.
omnidirect.omnidirect.
omnidirect.
omnidirect.
Channels (transmitter Gora Sw. Marcina)
-
22
60
35
-
-
57
Power
-
medium
mediummedium 10kW
-
-
high
Polarization-
H
H
H
-
-
H
Transm. antenna
-
omnidirect.
omnidirect.
directional
-
-
omnidirect.
List of programs transmitted from Krakow and Tarnow
Unfortunately, it is practically impossible to receive TVN, TV4, or Puls from Krakow - the direction of radiation is just opposite, towards the home city. So in Bochnia we have to use two UHF antennas (Krakow + Tarnow), and one VHF antenna (Krakow).
3. Angle distances among the transmitters. When signals come from several transmitters (at different locations), there is probability that they can be received with smaller number of antennas than the number of locations. To achieve such saving we should make use of characteristics of typical directional antenna - its half-power angle is ca 15 deg. So if the angle distance between two transmitters is within 15 degrees, the signals can be received with one antenna.
Example 2
Olesnica near Wroclaw. Reception from Wroclaw. In spite of three transmitters, we may take advantage of close angle distance. Only two antennas (VHF and UHF) will do the job properly.

Wroclaw

TVP1

TVP2

Polsat

TVN

TV4

Puls

TVP3

Channel

12

25

59

56

31

42

42

Powerhigh
high
high
medium
medium
high
high
Polarization
HH
H
H
H
H
H
Transm. antenna
omnidirect.omnidirect.
omnidirect.directionalomnidirect.omnidirect.omnidirect.
Transmitter's location
Mt. SlezaMt. SlezaMt. SlezaZorawina
Wroclaw
Mt. SlezaMt. Sleza
List of transmitters in/near Wroclaw
Example 3
Siechnice near Wroclaw. It will be rather possible to receive signals from Zorawina and Sleza with the same antenna. But the angle distance between Wroclaw and Mt. Sleza exceeds 15 degrees. So we recommend to use two UHF antennas and one VHF device.
4. Output power of the transmitters. The channels are transmitted at different power levels. The same TV tower may broadcast one channel at 300 kW, and another one at 10 kW. It is possible that some channels are ideal, whereas others very poor or practically not available.
Example 4
Lodz. In practice TV Puls is available only up to 5 km from the transmitter (TVN - up to 10 km. We should use two UHF antennas, and one UHF device (with signal equalizer). The weak TVN and PULS have to be amplified; in case of broadband amplifier there may be needed an attenuator for TVP2, TVP1, and Polsat channels.
The best solution is to employ channel amplifiers.

Lodz

TVP1

TVP2

Polsat

TVN

TV4

Puls

TVP3

Channel7

32

49 21565943
Power

high

100 kW

high

high

100 kW

medium

1 kW

medium

10 kW

medium

1 kW

high

100 kW

Polarization H H HHHHH
Transm. antenna
omnidirect.  omnidirect. omnidirect. 
Transmitter's location

Zygry     n. Sieradz

 Andrzejewska St

Andrzejewska St

 Sienkiewicza St
Andrzejewska StAndrzejewska StAndrzejewska St
List of programs available in Lodz and its surroundigs
5. Directivity of transmitters' antennas. Some antennas have directional characteristics. When outside a town/city, they usually are directed towards the town/city. This solution allows to optimize covering of highly populated areas, as well as to minimize interferences among signals from other transmitters.
Example 5.
The TVN transmitter Kosztowy (Silesia province) working in 32 channel does not cover south direction. So there are big problems with receiving this channel in Tychy (not so far from Kosztowy), whereas it is available even in the west part of Krakow.
6. Polarization. There are some transmitters in Poland that use vertical polarization. In this case the receiving antennas have to be mounted the same way i.e. with directors and reflectors arranged vertically. Vertical polarization is sometimes used by low-power transmitters that locally complement the transmission network. Due to opposite polarization they do not interfere with other transmitters.
Example 6
Bilgoraj, the transmitter Tarnawatka. The TVP1 channel is transmitted in channel 10 with vertical polarization, thus we have to mount VHF antenna so that its elements are arranged vertically.
7. Obstacles between transmitting and receiving antenna. It happens that the transmitting antenna is screened by an object e.g. mount, hill, high building. It is the reason why reception is impossible, even though the distance from the transmitter is quite short.
Examle 7
Skawina, near Krakow. The reception from Chorogwica (main transmitting tower for Krakow) is practically impossible. In such difficult situation the customer should look for the help of local installer who will probably be able to find satisfactory solution.
VIII. Kind of installation. We should remember that signal quality deteriorates after each next stage of distribution (worse S/N ratio). It means that in case of larger installations we should use better antennas.
Example 8
Selection of antennas depending on the kind of installation (up to 20 km from the transmitter).

 

1 TV receiver

Community installation

Small multiswitch installation

Large multiswitch installation

Broadband antenna (planar)

YES

NO

NO

NO

 Logarithmic antenna A4011

YES

NO

NO

NO

Antenna set
A0710+A1910

YES

YES

YES

NO

Antenna set A1116+A2682 or A3710

YES

YES

YES

YES

Selection of antennas depending on the kind of installation.
9. Influence of interferences, including unwanted signals from other transmitters. When we want to receive signals from several directions we should be prepared for the case of adjacent channels. Reception of such channels will be possible if they do not differ in level more than 3dB. Otherwise, the stronger channel will jam the weaker one.