[ntp:questions] Re: Why phase modulation
David J Taylor
david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid
Mon Jan 9 20:01:27 UTC 2006
Heiko Gerstung wrote:
> Hi, Rob:
> Rob van der Putten wrote:
>> Hi there
>> Why does DCF77's phase modulation (DCFp) offer a more reliable
>> timing then AM?
> From our DCF77 info page
> (http://www.meinberg.de/english/info/dcf77.htm): "In order to
> increase the accuracy of the demodulated time marks, the carrier of
> DCF77 is additionally modulated with a pseudo-random phase noise. The
> pseudo-random sequence has a length of 512 bits which are transmitted
> in the time interval between the AM marks. Due to the pseudo-random
> characteristics of the sequence, the mean deviation of the carrier
> phase is still zero. The phase modulated carrier can be received with
> a larger bandwidth. Correlation algorithms known from satellite
> techniques let PZF receivers determine the correct time with an
> accuracy of some microseconds which is much superior to the accuracy
> achieved by standard AM receivers."
>> Who produces these recievers and what do they cost?
>> Is GPS better or cheaper then DCFp?
> AFAIK we (Meinberg) are the only vendors offering such a technology.
> See for example:
> NTP Time Server with PZF receiver:
> Radio Clock Module
> (this one can be ordered as a standalone rack-mountable system with
> power supply and housing)
> and any other products with a "PZF" in their name :-)
> Kind regards,
Your stuff looks absolutely wonderful - I just droll and wish I could
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