Satellite television

Satellite television is a communication service that delivers programming directly to viewers.

It functions by relaying signals from a communications satellite orbiting Earth to a specific location. This technology is vital because it provides television to remote geographic areas. These regions often lack terrestrial television or cable services. The service relies on a complex chain of hardware to move data through space.

The process begins at an uplink facility on the ground. A transmitting antenna sends signals up to a satellite using a narrow beam of microwaves. These uplink dishes are extremely large to ensure accurate aiming and high signal strength. Once the signal reaches the satellite, it is caught by a transponder. A transponder is a device that receives the signal and re-transmits it back to Earth. During this step, the satellite performs translation. Translation is the process of changing the signal to a different frequency to avoid interference with the uplink. This return trip from the satellite to the Earth station is called the downlink.

Most broadcasting satellites operate in a geostationary orbit above the Earth's equator. In this specific orbit, the satellite's orbital period matches the rotation rate of the Earth. This means the satellite appears to stay in a fixed position in the sky. Because the satellite does not move relative to the ground, a home dish can be aimed permanently at it. This eliminates the need for expensive tracking systems. However, some systems use a Molniya orbit instead. A Molniya orbit is a highly elliptical path with an inclination of plus or minus 63.4 degrees. These satellites have an orbital period of approximately twelve hours.

Satellite technology has evolved significantly over time. Early systems were known as television receive-only systems. These used analog signals transmitted in the C-band, which ranges from 4 to 8 GHz. Because C-band signals were weaker, they required large dishes measuring 2 to 3 meters in diameter. People nicknamed these "big dish" systems. Modern systems primarily use digital signals and the Ku-band, which ranges from 12 to 18 GHz. Digital signals have much better spectral efficiency. This efficiency allows for high-definition television (HDTV) standards. Modern Ku-band dishes are much smaller, often less than one meter in diameter.

At the consumer level, the downlink signal is quite weak due to path loss. A parabolic receiving dish collects this signal and reflects it to a focal point. A device called a feedhorn or collector sits at this focal point. The feedhorn gathers the signals and conducts them to a low-noise block downconverter, or LNB. The LNB serves two critical purposes. First, it amplifies the weak signal. Second, it performs downconversion to a lower intermediate frequency (IF), usually in the L-band. This makes the signal easier to transmit through standard coaxial cable to an indoor receiver.

There are specific physical constraints on how many satellites can exist. Geostationary C-band satellites must be spaced at least 2 degrees of longitude apart to prevent interference. This limits the number of C-band satellites to 180. For Ku-band satellites, the spacing can be 1 degree, allowing for up to 360 satellites. Environmental factors also affect signal quality. C-band is susceptible to terrestrial interference. However, Ku-band is affected by rain and ice crystals in thunder clouds because water absorbs microwaves at those frequencies. Occasionally, a sun outage occurs when the sun aligns directly behind the satellite.

Once the signal reaches the home, a satellite receiver or set-top box completes the circuit. The receiver demodulates and converts the signals into video and audio. Some receivers are also integrated receiver/decoders (IRDs) that can unscramble encrypted channels. While some channels are free-to-air, many require a subscription. The transition from expensive C-band hardware to cheaper LNB and coaxial technology allowed the industry to move from a hobbyist market to mass production. Today, satellite television remains a cornerstone of global communication systems.