[ntp:questions] Re: Sure RPC DCF77 clock under Linux?

Ulrich Mueller ulm at kph.uni-mainz.de
Mon Jan 9 10:56:45 UTC 2006


I wrote:

> From the pattern of the telegrams (see my previous posting) I would
> conclude that the reception is o.k., but somehow an additional bit
> (or pulse?) gets inserted at the beginning.

> Maybe I should use an oscilloscope and look at the pulse train from
> the receiver?

Here it is, looking at pin 2 (RxD) and triggered at the time of the
minute marker:
<http://wwwa1.kph.uni-mainz.de/users/ulm/ntp/sure-rpc.png>

At second 0 there are _two_ pulses: The first pulse starts at 0 ms and
is 102 ms wide. The second pulse starts at about 200 ms; however, it
has no precise timing, I have seen times between 200 ms and 225 ms.
The pulses for the following seconds look o.k.: they start at 1000 ms,
2000 ms, etc.

Does anybody have an explanation why there are two pulses at second 0?
Yes, the signal always looks like this.

(And why does the software interpret the second pulse as valid? It is
completely out of time since it doesn't start at a full second.)

Regards
Uli




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