05 May, 2009


OK. This post should not surprise anyone following my blog.

I'm elaborating on my knowledge of geostationary communication devices.

i.e. satellites

First off, satellites orbit a space-region known as the "Clarke Belt", approx. 22.300 miles (35.888 km) above the equator. Each satellite has a number of 'transponders' (transmitter-responder), and each of these transponders carry a signal back to earth. These signals are carried either on "C band", "Ku Band" or "Ka Band" which signifes what frequency is used to transmit the signal. After travelling through our atmosphere, over 20.000 miles, a dish is able to recieve them.

A satellite-dish can be everything from 18" (inches) to 9' (feet) across. It's main purpose is to be a collector/reflector to catch a microwave-satellite-signal, and aim it towards the 'feedhorn'. The feedhorn recieves the signal and sends it to the 'LNB' (Low Noise Block). The LNB amplifies the signal, and converts it to a frequency more suitable for transmission over a cable, also known as an 'IFL' (Intra-Facility Link). The IFL then carries the signal to the satellite reciever/decoder.

In cases where the signal is digital video broadcasting (DVB), it is usually digitally encoded, and the reciever/decoder has to decode the signal before it can be viewed/used. This also enables satellite-feed vendors to offer more channels over the same bandwidth as used in analogue systems where the channel-capacity is limited by actual transmission-capacity.

The standard audio/visual encoding used in DVB is one of either MPEG2 or MPEG4.


Just a little side-note on the 'smartcards' used in DVB-transmission and decoding. Smartcards have always, since the beginning of satellite-TV, been the authentication-token used to retrieve encryption-keys for encrypted streams, or simply as an identification-device to identify the recieving party as a valid customer.

Early in the race, these cards were merely electronic storage-chips used for ID information. But after years of development, they incorporate a range of security technologies of which the card-vendors have licensed as  proprietary intellectual property.

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