> ...I must admit, the tri-state PC did look good > too until you pointed out the dead zone. I had assumed this > would be insignificant, but of course it can't be. I'll still > try the 74HC7046, but use the XOR PC instead.
How about switching between the 4046's phase detectors, once the PLL has locked? Or using a phase comparator like the AD9901 which has a "no dead zone" XOR phase comparator coupled with a frequency comparator? The later one can easily be put into a small cpld if you like. Best regards Ulrich Bangert > -----Ursprungliche Nachricht----- > Von: [email protected] > [mailto:[email protected]] Im Auftrag von gonzo moto > Gesendet: Montag, 10. August 2009 14:39 > An: time-nuts > Betreff: [!! SPAM] Re: [time-nuts] PLL question > > > > > Date: Fri, 07 Aug 2009 18:35:12 +0200 > > From: Magnus Danielson <[email protected]> > > > >~ > > If possible, keep the comparator frequency fairly high and avoid > > charge-pump detectors (according to my experience with > cheaper-tronic > > onces where dead-band created low rate wanderings while > simple designs > > excelled in stability). > > > > Using a low phase-noise oscillator for cleanup is a wise > idea, even if > > no frequency multiplication occurs. Active loop PI-regulation of > > sufficient bandwidth suppresses most of frequency trackings of the > > oscillator, so long-term stability is less of an issue where as > > phase-noise plots are. > > > > Cheers, > > Magnus > > Hi Magnus, > playing with my prototype (using a 74AC86 XOR) showed that > the lock-up time varied from 30sec to almost 5min. Because of > this variation, I decided to use a 74HC7046 because of it's > 'lock detect'. I must admit, the tri-state PC did look good > too until you pointed out the dead zone. I had assumed this > would be insignificant, but of course it can't be. I'll still > try the 74HC7046, but use the XOR PC instead. > > > > >------------------------------ > > > > > > > >Date: Fri, 07 Aug 2009 10:44:42 -0600 > >From: Ed Palmer <[email protected]> > > > > > >Which software version do you have, NMEA or Motorola? If > you have the > > > >NMEA version another question pops up: Should you do the division > > > >externally, or program the unit to directly put out the lower > >frequency? > > > > > > > >Ed > > > > Hi Ed, > I have the NMEA version. > If the decision was to run the PLL (PC) at less than 10MHz, > (as per my first build), I've run each signal through half a > 74HC390. I hopped this would avoid any device-to-device > variation and any device introduced error would be consistent > in both signals. > > >------------------------------ > > Date: Fri, 07 Aug 2009 10:52:17 -0600 > > From: Ed Palmer <[email protected]> > > > > Navsync doesn't really call it a synthesizer, they call it a > > Numerically > > Controlled Oscillator (NCO). My tests suggest that they're > doing what > > others have done on the 1 PPS output - change the state of > the 10 MHz > > output (high to low or vice versa) on a transition of their > internal 120 > > MHz clock. This means that you occasionally get a pulse > that's ~8 ns > > shorter or (presumably) longer than normal. My unit puts > out a short > > pulse about 200 times per second. Navsync has an app note > where they > > say that for some applications a phase-locked cleanup > oscillator will be > > required. > > > > Ed > > Thanks again Ed, I was unaware of the occasional distorted pulse. > > > In case anyone has noticed, there is an ebay seller in > Calgary listing some CW12s. I do not believe these are the > NMEA version and his price (for used units) is 30% over retail. > > 73 > ian > > _________________________________________________________________ > What goes online, stays online Check the daily blob for the > latest on what's happening around the web > http://windowslive.ninemsn.com.au/blog.aspx > _______________________________________________ > 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. _______________________________________________ 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.
