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Sending Picaxe Data Over 477MHz UHF CB

Interested in sending digital data over UHF CB? That's just one more thing you can do with a Picaxe.

By Stan Swan

There’s perhaps no finer recent example of remote communications than the Huygen space probe pictures direct from Saturn’s moon Titan.

Click for larger image

Even at the speed of light, these ultra-weak digital signals took about half an hour to reach Earth, yet were astoundingly clear!

Although such data signalling is naturally associated with the computer age, its basics date back well over a century to Morse code and Baudot teletype.

Data communication has had a rich history pre-dating even early electrical technology, with smoke signals, flashing mirrors, semaphore flags, marks in the sand, "1 if by land – 2 if by sea", green go/red stop lights and so on.

But back in the 21st century and terra firma, the cheap, licence-free 40-channel UHF CB sets mentioned last month have two channels (22 & 23) reserved for data transmission.

Australian/NZ regulations originally specified this data to have a duty cycle of just 3 seconds per hour, which presumably allowed for diverse services to timeshare the two channels, since three parts in 3600 is a very low ratio indeed. It was probably envisaged that much data would be simplex (one way) as occasional telemetry (measurement at a distance), indicating reservoir levels or telecommand (remote control) irrigation information, open farm gates, etc where changes over an hour would not be too dramatic.

However, in light of recent traumatic tsunami sea water level changes this looks far too conservative – in the real world many things may change horrifyingly fast, with the lack of such localised digital-age warning devices in stark contrast to Titan monitoring over a billion kilometres away.

Incidentally, www.manuka.orcon.net.nz/cbdata.htm links to data references and ACA UHF CB regulations.

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