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Old 23rd Dec 2019, 6:03 pm   #3
G6Tanuki
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Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: Radio controlled alarm clock query.

The clocks in current-decade cars generally use GPS or RDS - they get a pretty rapid 'time-sync', same as later VCRs and current PVRs sync their clock to over-the-air timestamps.

"radio controlled" alarm-clocks, and my radio-controlled wall-clock in the shack -- yes they do seem to take a while to 'catch up', even in a relatively RF-quiet environment. I'm not sure if the 'radio' bit of such clocks runs continually, or whether (as I suspect) it only fires-up occasionally to listen for the time - this would be much better as a battery-conservation strategy.

[In times-past I had a lot to do with the Internet "Network Time Protocol" - the strategy here being to take repeated time-sync data from several sources of different quality and use this to make minor, incremental changes to the local-clock. Eventually the local-clock 'converges' on the external-clocks and harmony is achieved. There may be user-definable constraints applied to whether you 'publish' the local-clock for use in timestamps in logfiles, financial transactions etc. if it is too divergent from the external clocks.

In a way it's a bit like the "Huff and Puff" VFO-locking-to-a-crystal scheme!

See https://en.wikipedia.org/wiki/Network_Time_Protocol for more info]
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