On Thu, 12 Jan 2006, Enrico Schuerrer wrote:

> Due to the synchronizing technology of a TV the V + H rates are not exact
> what you can name a "standard".

I agree, but integrating pulses over 24 hours will be *much* more 
accurate than mains, especially in third world countries (when receiving 
programs from sattelites or transmitters in first world countries).

> A much easier way is to use an ISDN telefon line or if  a SDH/SONET
> transmission line with operators tact is in use to apply the tact frequency
> to a quartz oscillator for synchronizing . The ISDN line tact or the
> transmission line tact is in minimum bound to a time signal broadcaster
> (better than 1 ^-12), mostly to a caesium or rubidium atomic clock (better
> than 1 ^-16).

I agree, but the digital streams that come down from a sattelite or from 
cable have the same potential accuracy, when integrated over a long time 
(24 hours or more).

Even with short integration times (say 1 hour) the accuracy can be 
increased to better than 2ppm. F.ex. an AM transmitter sending at 
nominally 1MHz and stabilized to 0.2ppm using GPS, and used over an hour 
can sync a PIC that runs on a 16MHz crystal to the nearest 0.5ppm at 
least. That's about one second per month for a clock.

Peter
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