Satellite TV Reception and Distribution Systems
Satellite TV Reception
Capabilities of Satellite TV
Satellite TV reception offers several advantages:
- Reception of numerous channels in various languages.
- Access to TV programs and channels in areas with challenging terrestrial signal reception.
- Catering to the demands of individuals residing abroad who speak specific languages.
Geostationary Orbit
Satellites are positioned in a geostationary equatorial orbit, where the Earth’s gravitational pull and centrifugal rotation are balanced. This orbit is located approximately 36,000 kilometers above the equator. Satellites in this orbit travel from west to east at a speed of 11,000 kilometers per hour, matching the Earth’s rotation. This synchronization creates the illusion that the satellite remains stationary in space.
Modular Structure of a Satellite
A satellite typically comprises the following modules:
- Antenna Module: Responsible for transmitting and receiving signals.
- Communication Module (Transponder): An electronic system that converts the uplink frequency to the downlink frequency.
- Power Module: Provides the necessary power for satellite operation.
- Service Module: Houses essential support systems.
- Propulsion Module: Enables adjustments to the satellite’s position and orbit.
Orbital Position of Satellites
The orbital position of a satellite is defined as the angle formed at the Earth’s center between the Greenwich Meridian (a reference point on the equator) and the satellite’s location.
Frequency of Satellite Transmission Signals
Satellites utilize microwave frequencies for signal transmission. In Europe, the downlink employs the KU band, further divided into the FSS lower band and FSS upper band. Polarization (linear – vertical and horizontal, or circular – right or left) is used to expand the number of channels. Channel separation in the KU band varies, with high-band channels spaced 39 MHz apart and low-band channels spaced 29.5 MHz apart.
Area Coverage of Satellites
The coverage area of a satellite is determined by the configuration of its transmitting antenna. The beam width of the radio frequency signals emitted by the antenna dictates the size of the coverage area. Satellites can have multiple beams, including global, hemispheric, zonal, and spot beams.
Technical Considerations
- Beam Width: Influenced by the size of the satellite dish, the beam width determines the coverage area. A wider beam width provides a larger coverage area.
- Power Radiated by a Satellite (PIRE): Expressed in decibels relative to 1 watt (dBW), PIRE represents the power radiated by the satellite. A higher PIRE allows for the use of smaller receiving dishes.
- Gain: Measures the amplification of signals received and transmitted by the antenna.
- Efficiency: Represents the percentage of energy incident on the dish that is successfully focused.
- Secondary Lobe: Indicates the antenna’s ability to receive signals from areas outside the main beam.
- Attenuation: Signal loss that occurs during transmission between the Earth and the satellite, as well as during reception. Atmospheric conditions and distance contribute to attenuation.
- Directivity: A measure of the antenna’s ability to focus the signal in a specific direction. High directivity is desirable for efficient signal reception.
Distribution System of the Satellite TV Signal
Distribution Channel Processor
The distribution channel processor converts the intermediate frequency (IF) signal to VHF or UHF frequencies for distribution. It consists of tunable indoor units, each dedicated to a specific channel. Two main models exist: Double Sideband (DSB) and Vestigial Sideband (BLV) modulation systems.
Basic Procedures
- Narrowband or Single Channel RF Processing: Each tuned channel is converted into a TV channel and amplified.
- Broadband RF Processing: Each tuned IF channel is converted to a TV channel, mixed with terrestrial TV channels, and amplified.
Advantages and Disadvantages of the Processor Distribution System
- Advantages: Compatibility with collective living facilities, utilization of existing terrestrial TV distribution networks.
- Disadvantages: Cost increases with the number of channels received.
Components of the Processor Distribution System
- IF Signal Splitter: Distributes the IF signal to the tunable indoor units.
- Indoor Units: Demodulate, process, and modulate the signal for a specific channel.
- Power Supplies: Provide the necessary power for the indoor units.
- Amplifier Units: Equalize signal levels from the indoor units.