Gents, I have been an admirer to Stanford Research since many years. That is why I thougth: Hey man, if they are that friendly to explain their PLL in THAT detail in the PRS10 handbook I take them as my school masters and make the regulation in my DIY GPSDO pretty much the same. The PRS10 features a (switchable) pre-filter for phase data that automatically gets 1/3 the time constant of what the main loop filter is set to. This pre-filter is thought to de-noise the data before it even enters the loop. Since I have access to all stages of the data processing in my GPSDO I attach a graph showing
1) Red line: Raw phase data, as delivered from phase comparator (RX = M12+) 2) Blue line: Sawtooth corrected phase data 3) Yellow line: Phase data behind the pre-filter May everybody judge for himself which of the lines is more suitable as the input of a regulation loop. Unfortunately the original PRS10 does not feature the facility to process sowtooth data and considered in detail this limitation even makes sense: In order to make things easy for the user they would have to make their microcontroller talk to the receiver in its specific language which is by no means standarized but is not only different between manufacturers but also between different generations of receivers (at least concerned Motorola). The alternative would have been to include a command in their own PRS10-syntax which would need an external online translation process from receiver language into PRS10 language and who of you owns a device that would accomplish this task on the fly WITHOUT writing a special program for it? There we got it! As far as I can see the PRS10 is one of the very seldom cases that would benefit from generating a new sawtooth corrected pps signal in hardware. Best regards Ulrich Bangert > -----Ursprungliche Nachricht----- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von christopher hoover > Gesendet: Freitag, 25. April 2008 05:36 > An: [email protected] > Betreff: Re: [time-nuts] Disciplining Rubidium > > > Said wrote: > > > For such a large phase error I would have expected the > PRS10 to just > > reset > > > the 1PPS rather than drift it. > > The PRS10 uses a straightforward second order PLL to lock > itself to an external 1PPS, so you will see a frequency error > on phase jumps as it has to slew the frequency to get back on phase. > > There's a quite detailed description of the PLL in the manual. > > Incidentally, it is my experience that the PRS10 behaves > fairly poorly if you simply feed it 1PPS without sawtooth > correction. I'm in the midst of a move so I can't relate > numbers at the moment. > > (Someone once mentioned of a firmware upgrade or a magic > command or something to allow you to feed the sawtooth > corrections from the receiver to the PRS10's time tagging > circuit, but I've yet to find any documentation on > that.) > > -ch > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > and > follow the instructions there. >
PRS10.pdf
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