SatComs, or satellite communications, encompasses a wide range of satellite uses. In layman’s terms, communication by satellite is the act of bouncing a signal transmitted from Earth off a satellite and back to a different point on Earth. The advantage of this is that it gives us the ability to communicate quickly with anyone, anywhere on Earth.
Today we use SatComs to transmit digital and analog signals that provide us with information about weather patterns, the condition of earth’s ecosystems, and of course for GPS technology, to name a few. Satellite television providers also use this technology to transmit programs to customer’s receivers, and portable satellite phones are still the most reliable communications devices in remote geographic areas.
How Does it Work?
As noted earlier, the satellite receives a signal from earth and sends it back to a different (or the same) receiver. Before a satellite can bounce a signal, however, it has to be sent up into orbit. Satellites use various orbits, including:
-Geostationary
-Molniya orbits
-Elliptical orbits
-Low Earth orbiting
A geostationary orbit follows the Earth’s rotation and orbital period. These satellites are typical for communications and weather transmissions.
Molniya orbits are elliptical orbits that are inclined at a degree to avoid being disturbed by the Earth’s gravitational field. To get a satellite into Molniya orbit uses less launch energy than one for a geostationary orbit. At the same time, a satellite in this orbit can reach higher latitudes while expending less power.
Elliptical orbits, like the Molniya orbit, trace an oval-shaped route of a celestial body.
Low-Earth orbiting refers to those satellites orbiting no more than 250 miles above our planet’s surface. These satellites are less expensive to put into orbit and can operate with weaker signals.
Today’s satellite communications not only send the signal back, but convert it to a different frequency and send it back stronger. This process is called amplification and is done to avoid confusing the signals coming and going.
Links
When a radio (analog) or digital signal is sent to a satellite it is called an “uplink.” When it is sent back from the satellite, it is called a “downlink.” In order for the amplified downlink to reach its intended targets on earth, the signals are sent to feeder stations engineered to transmit these signals to specific receivers on earth. A perfect example of this is a television company transmitting signals to its customers.
Direct Broadcast
With the extensive development of digital cable TV using fiber optic cable to transmit signals, it might seem like satellite television is obsolete. However, satellite communications is still the best method of delivering comprehensive television programming in remote regions or areas established in mountainous terrain. The term “direct broadcast” refers to the fact that customers receive signals directly from the geostationary orbiting satellites. To receive this signal, customers allow the provider to install a dish antenna, which is usually 2 to 3 feet across.
While satellites are used extensively in everyday communications and television, they are vital to certain military and industrial applications. These satellite communications functions will be covered in the next post. Stay tuned.
MJS Designs has been providing electronics design, assembly and engineering to the satellite industry for close to 35 years. Visit us online at www.mjsdesigns.com or like us on Facebook for the latest updates and information.