Neil Hopcroft

A digital misfit

Todays revelation is that not everybody knows that the electricity companies use a Radio 4 sidechannel to broadcast metering information. I thought every techie knew that, but the only reference I managed to turn up in a(n admittedly brief) web search was AMSS – the data rate isn’t high, 46 *bits* per second.

Does anyone know any more about such channels, and what kind of information gets broadcast over them?


Categories: Memories.

/ 5 Comments

5 comments

  1. neilh

    Not very much, given the data rate.

    It started out as control for economy 7 off peak electricity, but I think theres a whole bunch of low data rate config things that use it these days. But I’m not really close enough to know the protocol or anything.

    It came up in the context of changing rates on prepaid electricity meters, which I speculated (without any particular grounds) used the same sideband.

    I was hoping someone would be able to fill me in a bit on the details I’m missing.

    Reply
    • cabbage

      How much do you want to know? :) How much am I allowed to tell you? :(

      The communications parameters and packet format are specified in BBC Research Department Report 1984/19. You will note that different user codes are available; presumably the electricity companies have one set aside.

      The BBC also uses the system (presumably why they devised it in the first place!).

      Reply
      • neilh

        Its all coming flooding back now, I remember considering that as a source of time-codes ten years back, but the resolution was so poor that we couldn’t make it useful…GPS had the other problem, too much resolution, to the point that by the time you’d processed its nanosecond accurate signal it wasn’t right any more. We opted for an internal timer instead, relying only on the crystal accuracy, which was enough since our sensors ran on a 40k cycle anyway.

        Reply
  2. neilh

    Its the demodulating that makes it interesting…

    …46bps would be detectable by ear if you were to remove (or reduce the time of) the AGC in your radio.

    Reply

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