A satellite is an object that orbits a larger object. With this definition planet earth is called a satellite relative to the sun. Another example is the moon relative to planet earth. These are natural satellites that exist long before man was created. Man studied these and designed artificial satellites to enhance his living conditions. They all have different purposes the most common of which is satellite television. There are so many artificial satellites in orbit some with similar functions while others serve other functions. Some also have multi function serving more than one purpose.
Satellite television (TV) delivers tv programmes using radio frequency (RF) signals from artificial satellites in orbit. They are positioned about 20000 miles above the earth surface. Since the earth rotates within 24 hours and revolve 365 days satellites are designed to move with same speed. This keeps them in one place relative to the earth. That means signal sent from one satellite will always serve one location at all times.
Satellites have a lifespan of about 15 years after which they are self destroyed. Although they are built mostly to use solar energy to power their activities throughout their life cycle.
The Circle Of Transmission Of Satellite TV
A good example of a satellite tv provider is Startsat. They get their programmes from two major sources: National Turnaround channels and various local channels. Turnaround stations normally send their signals upstream to the satellite itself like CNN but local stations like Delta Broadcasting Service (DBS) Warri typically broadcast their programmes over the airwaves. To get these local programmes upstream satellite providers receive local signals from a broadcaster using big antennas or high capacity cable. These signals are further sent to their broadcast centre.
The next step is the uncompression of the analogue signal receive and conversion to digital format. This format is then compress and sent to the satellite in space using large dish at a particular frequency. The satellite must be tuned to that frequency to be able to pick up the signals. Due to distance the signal gets weak before it reaches the satellite. The satellite increases the frequency of the signal receive and beam it to the customers on earth. The signal can only be received by customers who are within the calculated area and have the right equipment to capture the signal. One satellite cannot serve the whole world.
The customer needs a set of equipment to get the signal to play on tv. The first thing the signal gets to is the satellite dish. When tv broadcasting started signals were weak due to satellites sending signals at low frequencies. This made it difficult getting signals easily. To solve that, customers were made to install large dish as much as 4 metres to get signals. Today due to the advance in technology a small dish can capture same programmes although big dish still have some of its advantages which we will not discuss here.
The signal the bounce off the dish at an angle into the hollow Low Noise Block (LNB). This small piece of equipment found at the front of your dish is not the first thing that picks signal from your satellite. The signal received from the dish is then relayed to your set-top box popularly called decoder in Nigeria through cable. The function of the decoder is to convert the digital signal received to analog if the tv set is an analog tv and also to decrypt encrypted channels.
The initial broadcasting was done using broadcast towers which transmit RF signals in the very high (VH) and ultra high (UH) frequency range. The disadvantages to this method were so great that engineers have to think of better alternatives which lead to satellite tv. Others include;
- cable tv: In which tv signals are sent in cables using RF cables
- Terrestrial tv: Signals transmitted by radio waves from earth based stations to antennas connected to home tv
More will be discuss on them.