[ntp:questions] Tobit LAN!Time DCF77 receiver not working

David Lord snews at lordynet.org
Wed Jan 6 18:33:23 UTC 2010


Rob wrote:
> David Lord <snews at lordynet.org> wrote:
>> I'm pretty sure us accuracy is available at closer range
>> since it is possible to sync to exact cycle of carrier
>> with period of around 13us, ie to within a fraction of
>> that so 1us shouldn't be a problem.
> 
> The problem is not in the accuracy of the transmitter or your
> capability to receive it, but in the path between transmitter
> and receiver.
> I have both DCF77 and GPS receivers connected and there is a very
> clearly visible change in the relative offsets between those
> over a day/night cycle.  This is of ms order of magnitude.

Are you on a pps signal from DCF77 as well as GPS?

With DCF, I see complete loss of signal, I assume due to skywave
cancellation of groundwave, for a couple of periods most days, and
order of ms shift during period at night when signal comes back.

I did state "closer range" but I don't track propagation delays vs
frequency so don't know at what distance it becomes unreliable.

There must also be means to compensate to some degree for the
longer range as the disturbances are periodic.

MSF at 160km with PPS seems to be +/-165us and that's without
any attempt to lock to the carrier but there is no equivalent
to lock to a particular cycle as with DCF77 or TDF.

David




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