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July 16, 2007

by Brian Turner

I’ll be honest. This is partly about footprint maps, and partly an excuse to have a ramble. A chance to put down on e-paper a small percentage of the obscure things that I’d like on record should I ever be assassinated by the KGB, or dare I say it, BSkyB.

What are satellite footprint maps?

Well, like a torch beam focused on a wall, invisible beams of microwave radiation ‘shine’ down on the planet from a whole range of satellites in space.

Be they commercial or military, they each act like a huge mirror - more or less. They take their signal from large powerful “Earth stations” which upload information (TV, radio and data signals) to the spacecraft where it is amplified and sent back to Earth.

Sounds pretty pointless on the face of it, but the shape and sheer coverage with which these signals return to us can be a very powerful tool. Again, much like a torch beam, the shape can be altered - squeezed and manipulated to target those areas requiring reception - and equally to avoid those countries for whom the signal is not intended.

The reflecting satellite technique also allows those distributing the transmissions to overcome limitations found here on Earth with terrestrial broadcasts - where the shortcomings of living on a large spherical object invariably spoil their fun. Things like the curvature of the Earth itself and unpredictable atmospheric conditions.

So about these footprints - what does it matter to me?

Well it might matter, if (for example) you ever move to Spain and long to see Eastenders again.

OK, so you have no plans to move to Spain, and nobody is ever going to mourn the loss of Eastenders, but these footprints get more interesting the further you move from the middle of the beam.

Hey! Who said anything about moving?

Let’s say you subscribe to Sky UK. Did you ever really stop to think about satellite TV in other countries? Did you ever think that the satellite signals might ‘spill over’ into bordering countries?

Well, it’s all kept a bit quiet really. In fact it’s a bit of an embarrassment to all concerned that in the European Union for example, where there is supposed to be free trade across our borders, and an end in sight to ridiculous price differentials from one country to the next, the issue of satellite TV is a huge lump under the carpet.

It was swept under there a long time ago, and yet, try as it might to work it’s way to the skirting board for a lungful of dust-free air, it suits most large players (both political and commercial) to keep it right where it is.

One of the aims of the Satellite Help project is to free that lump - to publicise the fact that there are maybe 80 satellites in the visible sky above the UK - most of which you can receive something recognisable from with only modest equipment.

And that’s where the footprint maps come in. They help you estimate which satellite beams (and bear in mind that plenty of satellites have multiple beams) you can get a sniff of. The maps chart estimated reception power-levels in an isogram (like a contour line) - which is really geeky, right? Well, it also gives a very real translation into dish sizes required to receive that signal.

So not that geeky then!

From real world experience, these maps are not to be relied upon 100%. It’s true that local conditions can have a significant effect on signal strength and therefore required dish size, but it’s a good starting point. The forum here is a good place to go for further advice on what the likely hardware requirements are at any given location.

And there’s nothing better than local information to confirm theoretical figures.

We have been building up a large library of these maps in our Satellite Footprints board which, if you’ve read this far, you might just find interesting!

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