[time-nuts] Radio Controlled Clocks

[Andy Talbot]

With this talk of Radio Controlled clocks...
I have three domestic RC clocks here, receiving the UK 60kHz signal, MSF.
  However, I notice that when compared against a GPS clock, timed from the
1 PPS signal & NMEA output, they all are a few hundred milliseconds fast,
ie the display changes just before the GPS derived time.
My reasoning for this discrepancy is this:

The flag for the decoded MSF time signal is 01111110 sent during the 52 -
59 seconds intervals, so the flag appears at hh:mm:59 and the correct
procedure is to detect this flag, then wait until the next signalling edge
(drop in carrier) to define the minute epoch

All modern MSF clocks include a crystal filter, and this may have a
bandwidth typically of 2Hz, and a consequent group delay as a filter of ~
500ms.   SO...
I reckon the manufacturers cheat, go just for the :59 seconds point when
teh flag appears then rely on the crystal filter and LCD delay to give
"something like a second.   Since it's sure to be a bit less than this in
total, especially if the LCD is warm, hence the typically  100 - 200ms
delay observed.

I only ever have digital display clocks, so wouldn't know if the same
happens with round ones with hands.    Anyone else using domestic MSF or
DCF77 clocks who have observed this?

Andy
www.g4jnt.com