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Why are there 3 beams? |
| There's
an aspect of satellite TV that confuses many people. It's why are there
3 beams. Why can't all the channels transmit on a single beam so that
there's just one footprint on the ground? Why is it more difficult to
pick up the BBC and ITV than say Channel 4?
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| The simplest way of explaining the 3
beams is that there are 4 satellites in the Astra 2 cluster. They're
close together in space so that an earth-bound dish 'sees' them as a
single unit. Three of the four satellites, the 2A, 2B and 2C, transmit
north and south beams which between them cover the whole of western
Europe. (In fact that means there are 3 north and 3 south beams but
let's not get complicated, let's just assume there's one of each!)
Why SES-Astra opted to spread the beams the way they did, I don't know. However I suspect that when the satellites were designed, the company didn't have any firm customers for them so they were in effect hedging their bets. In the event, Sky decided to switch to digital transmissions and moved their operation from the Astra 1 system to Astra 2. Sky had plans for too many channels to fit them all on to a single beam and therefore space was rented on both the available beams. As they both covered the UK, they were suitable for Sky's purposes and the fact that they also covered vast swathes of the continent as well didn't matter because of encryption. The BBC, Channel 4 and Five (but not ITV which stayed aloof from satellite in order to promote its own, and ultimately ill-fated, OnDigital) also joined the Astra 2 platform and bought into the Sky encryption so as to limit their own spread outside the UK. Thus Astra 2 became essentially UK-orientated, and the Astra 1 system that had previously carried Sky's analogue signals was switched to European transmissions. A few years later as capacity requirements grew, the Astra 2D satellite was launched having been acquired at fairly short notice from Boeing, the manufacturer. By a happy coincidence, its beam was a narrow one which made it ideal for focusing tightly on the British Isles. One of the first broadcasters to rent space on the 2D was ITV which joined in 2002. Despite being on the 2D, ITV opted for encryption (a) because it wasn't sure how some of its suppliers (ie the American studios) would react to clear transmissions, and (b) in order to regionalise its output. What happened next was that the BBC realised the significance of the 2D's narrow beam, and decided to switch to it in order to transmit clear and save itself the cost of encryption. ITV then followed suite when its contract with Sky expired in November 2005. There is a potential problem however; the life of all satellites is finite (because they eventually run out of fuel to keep themselves from drifting off-station). In the case of the Astra 2D, its design life was 12 years and it was launched in 2000. Therefore it could become non-functional as early as 2012. Unless SES-Astra can obtain (indeed be persuaded to obtain) an equivalent replacement within the next few years, it could have consequences for clear unencrypted signals in the long term.
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