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Twitching with

A birdspotting wok, image courtesy of psand.netIt’s early afternoon on an overcast Bristol day and there’s a satellite dish set up in the car park of St Werburgh’s Community Centre. Inside the Bristol Wireless room, Mike Harris of is giving a packed room a brief introduction to communications using satellites (otherwise known as ‘birds’).

We cover the basics of satellite communications – geostationary orbits, low, medium and high earth orbits, footprints, dish size needed in relation to footprint, the effect of the earth’s curvature and how communications to and from the machines attached to the modem, dish (the combination of dish and modem are known as a SIT – Satellite Internet Terminal) and the internet are handled.

After a short tea break, we’re all outside ready for ‘birdspotting’ – trying to find Eurobird 3, a mere 35,000 km away above the equator at 33.0 degrees east (time to take a compass bearing) – and aligning the dish with it for the best signal strength.

With a box of tricks hooked up to the dish receiver, by swinging the dish left and right and cranking it up and down, we first found the Astra satellite (which has the most powerful signal and carries popular TV channels, such as MTV) as a reference, before tracking down Eurobird 3. Mike explained this was a very useful and time-saving technique. Once we’d found Eurobird, it was time to contact the satellite on the laptop via telnet and tweak the alignment (with BW network engineer Lloyd wielding the spanner…) to achieve the best possible connection.

This done, a web browser could be launched and all normal internet services accessed, albeit with the signals travelling 70,000 plus kilometres.

This setup is used whenever the Bristol Wireless LTSP suite goes on manoeuvres to sites with no ordinary wired network access, such as our recent summer outings.

All told, it was a very informative and enjoyable workshop. Thanks Mike!