[ntp:questions] Swiss HBG signal (was: Re: Sure RPC DCF77 clock under Linux?)

Ulrich Mueller ulm at kph.uni-mainz.de
Thu Jan 12 01:19:29 UTC 2006

>>>>> On Wed, 11 Jan 2006, Serge Bets wrote:

> If at plain hours you get 3 pulses of 100 ms, and twice a day 4 such
> pulses,

Indeed, at the full hour there are 3 pulses (starting at approximately
0, 200, and 400 ms) and at noon there are 4 pulses. I didn't check
midnight yet.

> then you are hearing the Swiss radio HBG on 75 kHz.

It looks like. But it is very strange, since the receiver should be
tuned to 77.5 kHz. Also, we are only 55 km away from Mainflingen where
the DCF77 transmitter is located.

> The coding is very compatible with the German DCF77. Drivers should
> be able to decode both, unless they choke on the different minute
> markers.

NTP doesn't like it: It inserts an additional bit for each extra
pulse, and then it cannot decode the telegram.

If I patch the inp_rawdcf function (in libparse/clk_rawdcf.c) to
discard all pulses that are less than 700 ms after the previous pulse
then the driver can decode the signal.

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