[time-nuts] How accurate are cheap radio controlled clocks?

David t_list_1_only at braw.co.uk
Sun Jun 26 18:15:42 UTC 2011

>>> I've got one of the cheap radio-controlled clocks? I was listing to
>>> radio 4 the other day and herd the time signal. The radio controlled
>>> clock was about 3 seconds off. I was a bit surprised it was so far
>>> off. I'm just wondering how accurate these things are.
>> David,
>> Be aware that if listening via digital radio (or worse, digital TV)
>> there is a delay in the transmission chain of up to several seconds
>> (DTV). I expect you know that already! Use the FM signal for best results.
> I was using 198.00 kHz longwave here in the UK. Unless there's some digital
> processing going on before the signal is AM modulated, this can't explain the
> problem.

I'd back what David Taylor says that I casually see my cheap Casio watch 
maintaining sync via the NPL Anthorn 60kHz signal within a second of BBC 
R4 LW pips although it appears we are in the same neighbourhood. I back 
the idea that the clock is not syncing for one of the aforementioned 
reasons (local noise, clock orientation etc). Bear in mind R4 LW at 
Droitwitch is not a single national service, there are two other 
transmitters that tend to be forgotten, the R4 198kHz signal Dave & I 
pick up may be the one transmitted from Westerglen rather than the NPL 
monitored signal from Droitwich (see 1). I've never seen anything 
authoritative regarding how the Scottish transmitters are controlled for 
carrier stability or modulation delay (audio or time code) nor anything 
about mutual interference zones. The NPL reports relate only to 
Droitwich carrier accuracy (2).

For the timenut, remember that R4 LW has a largely forgotten time code 
feature (3) which frees you from having to listen to the pips and John 
Humphrys, I wonder if anyone is monitoring this?

(1) http://en.wikipedia.org/wiki/Droitwich_transmitting_station
(3) http://downloads.bbc.co.uk/rd/pubs/reports/1984-19.pdf


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