Terrestrial TV Reception Systems: A Comprehensive Guide
Devices and Amplifiers Selection
Team Heading
To choose one, consider that the maximum output voltage provides a maximum signal level without distortion. This is linked to intermodulation and cross-modulation, which limit the maximum signal provided by the amplifier output without distortion. Intermodulation is typical of single-channel systems, while cross-modulation causes broadband mixtures or interactions between signals from different channels.
In broadband, to avoid cross-modulation problems, the amplified output signal levels for all channels must be very similar. With the Z technique, consider the following:
- In VHF, leave two unused channels between every two used channels.
- Place amplifiers from the highest to the lowest channel, removing power to the grid by the highest channel.
- When using an amplifier with two outputs, use the output connected to the power supply. When using only one output, connect a 75W load to the other.
In head-end equipment consisting of single-channel Z amplifiers, the maximum output level of the whole system is reduced compared to the maximum output level of each amplifier separately.
When amplifying adjacent channels through connected single-channel Z amplifiers, arrange the amplifiers in two or more groups with an equal number of amplifiers. Place and connect the amplifiers of each group by varying the channel, taking power from the highest channel or the power supply of each group. The disadvantage of this mounting method is that each group has its own TV signal output.
Converters
Converters transform the TV signal to a channel other than the transmission channel. Reasons for using a converter include:
- All system components have greater attenuation in a specific band.
- The TV signal level is very high, causing double images or ghosting.
- Channels from neighboring countries or regions transmit on very high frequencies, making reception difficult.
Characteristics
- Maximum output power
- Adjacent channel rejection in dB (the higher the value, the better)
- Noise factor in dB (the lower the value, the better)
- Channel handling capabilities
Filters
Filters remove specific frequencies when adjacent channel interference or other disturbances occur. They prevent unwanted signals from passing through by attenuating them up to 30dB. Filter types include:
- Low-pass filters: Remove all TV signals above a certain frequency.
- Suppressors: Tuned to specific TV signal frequencies for removal.
- Band-pass filters: Allow reception of TV signals within a specific frequency range.
Install filters before the amplifier to relax or remove unwanted signal frequencies. Sometimes, multiple amplifiers are necessary to ensure strong signal attenuation.
Features
- Channel(s) passed or attenuated
- Insertion loss
- Adjacent channel rejection
- Number of inputs
Mixers
Mixers combine multiple input signals and introduce the combined signal into the distribution network. They combine TV signals captured by one or more antennas, which may correspond to different channels within the same band or different bands. Mixers can be mounted on the antenna mast, amplifier output, or incorporated into antennas.
Features
- Attenuation of each channel (input-output voltage loss in dB)
- Bandwidth
- Decoupling between inputs (should be less than 20dB)
- Number of input channels
Equalizers
Equalizers balance the output levels of TV signals. They are installed directly at the input of amplification equipment and receive the signal directly from the antenna(s).
Attenuators
Attenuators decrease the level of received TV signals. They are connected before the amplifier and can be mounted directly on the amplifier input using a connector. Attenuators have the same impedance at the input and output.
Network Distribution Systems for Terrestrial TV Reception
The distribution system is crucial for TV installation and should be designed to provide good signal levels to users. TV signal distribution is typically done using coaxial cables from the headend output to the user outlets.
Distributors
: used when you have an outlet and you want to have different output signal source to serve through the coaxial conductors. When the output is not used will close with a resistance of 75W.Las attenuation characteristics are passing through or insertion losses, rejection between outputs (shown as an output parasitic signals affect the rest of them, in dB and the higher higher quality value to be the dealer) and adaptation of inputs and outputs (it is very important that the values of the impedances at the inlet and outlet of the distributor are the same value to avoid loss or attenuation of the TV signal). The types are: resistive splitters (consist of a group of resistors calculated to produce a balanced distribution of the output signals. The facility employs user few shots), delivery inductive (are made of a material plate insulation in which several coils are mounted on a copper ring, which has less insertion loss and elimination of any spurious signals from another TV). – drifters: used in a point of the distribution decreases where there are several downloads of it and need to obtain one or more shots per user or home, with elements that are used to distribute the signal distribución.las network features are: attenuation of step (given in dB and indicates the attenuation of TV signal distribution network through the shunt, and is between 0.5 and 3.5 dB) attenuation of derivation (it is in dB and indicates the loss or attenuation occurs in the shunt to remove part of the TV signal to service or provide the signal to a TV or home, and rejected out (shown in dB as affect other parasite signals output or bypasses existing one, taking as values those greater than 25dB). Therates are: resistant (consists of a grouping of different resistances. There is a cdt calculated by the manufacturer to produce the necessary attenuation of both shunt and insertion or step on the basis of the specific location of the shunt to the side of head), inductive shunt (medium consists of high frequency transformers toridales to have a lower attenuation decreases as the frequency of the TV signal.) User-sockets: a device that allows connection to the network of computers user to access the different services it provides. This falls within the internal network user, having its origin in the PAU. The PAU marks the end of the network of dispersion, which is the network that links the distribution network within the network user. Can be: user takes step (installed on the user’s internal network so that it continues to other forms of way) and making the end user (the last one is connected). The features are: connection attenuation (in dB and indicates that lose in taking the TV signal that comes through the coaxial conductor, depending on the plant will use larger or smaller), attenuation of step (refer to the jacks in passing that had the lowest attenuation possible step so that the next shot you can have the highest signal values possible) and rejected shots user (typical user footage showing different outlet for TV radio, indicating the attenuation in making suffers TV and radio signal attenuation in making radio signal suffers TV). The types are: resistive shots (they are formed by a cluster of resistance values appropriate to the attenuation of step and tap to be produced at the facility, increasing the value of both attenuation with increasing frequency) inductive footage (consist of a grouping of coils and are separated from radio and TV, being integrated into the pre-filter takes a radio and TV connector) and hybrid shots (they are a mixture of resistive and inductive, presenting such a rejection value between the outputs than 25dB, being inadequate to a facility with a high number of shots and TV channels that are captured).