Introduction to satellite TV

The concepts behind satellite broadcasting were initially stated in Arthur C. Clarke's article in October 1945 edition of Wireless World magazine. Signals are beamed into space by an uplink antenna, received by an orbiting satellite, electronically processed, broadcasted back to Earth by a downlink antenna and detected by an earth station located anywhere in the satellite's footprint. 

All Direct-to-Home broadcast satellites are located approximately 35,800 km away from the Earth's surface above the equatorial plane. This region has been known as the Clarke Belt because it was Arthur C. Clark who, in 1945, worked out that an object in this position in space would appear to be stationary from the Earth's surface, hence the term geostationary orbit. In other words, each satellite appears in one fixed orbital slot in the sky, and a fixed dish antenna can be permanently aimed towards any chosen geostationary satellite. 


The satellite signal
The power coming from the geostationary satellite is incredibly weak. The satellite transponder power was typically 20W in the '80s. To give you some idea, imagine trying to see a 20W light bulb 36,000 km away - anyone would have trouble seeing a 20W bulb 50 meters away! This is difficult enough on a totally clear day, so now imagine the cloud, mist, fog, rain and snow in the way and you are a little closer to how difficult it is to receive satellite signals. 


Receiving the satellite signal
A typical satellite receiving system basically consists of three components: The antenna or else satellite dish, the feedhorn/ Low Noise Block (LNB) assembly and the satellite receiver. The dish collects what little it can of these signals and reflects the signal back into the feedhorn of the LNB. The feed/LNB has to be positioned at the focal point of the antenna for highest efficiency. It has then to amplify the incredibly weak signal without adding any appreciable amount of any unwanted signal (or noise), hence the term "Low Noise Block". In the old days, LNB noise figures were high (typically between 2.0 to 2.5 dB). Nowadays, technology has been significantly evolved, satellite transponders can typically produce 50W or 60W and LNBs have higher gains and lower noise figures (typ. 0.6 dB), which makes satellite TV reception feasible with dishes being as small as 40cm in diameter!

The most popular satellite TV band, the Ku band frequency extends from 10.70 to 12.75 GHz. This signal is too high for the cable and the indoor receiver. So, the LNB has to downconvert the Radio Frequency. It does this by mixing the RF signal with a frequency generated by the LNB itself, the Local Oscillator (LO). The LNB needs its own very efficient internal screening to ensure the internal LO frequency doesn't mix at the wrong time. You need a little more amplification of the wanted signal and some filtering. What comes out of the LNB is the Intermediate Frequency (IF) which is the RF minus the Local Oscillator (LO) frequency. This typically ranges from 950 to 2150 MHz for Ku band and can be handled by the cable and indoor receiver. The signal is then fed through a low loss co-axial cable to the satellite receiver, whose function is to select one channel from the block of frequencies relayed from the LNB and then to process this signal into a form acceptable by a television set. 


The slightest improvement makes the difference
There are plenty of satellites, nowadays, that can easily be received with relatively small dishes and virtually any kind of suitable satellite gear. This does not hold true, by any means, if the satellite signal is weak. Where a weak analogue signal might have a picture with terrible sparklies, a weak digital signal can give a blank screen and no sound. To get pictures from the weakest signals, losses have to be minimised and system components have to be properly installed and precisely tuned to the satellite. Even if we are looking at something like only 0.1 dB (or approximately 2%) improvement, this can make the difference between receiving a watchable digital transmission and receiving a bunch of coloured squares. Here is where TITOSAT satellite experts excel, in delivering the best available signal from the best satellite system components; and that's what gives us the precedence against the competition.