> 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.
