[time-nuts] Any Spectracom hackers out there?

John Ackermann N8UR jra at febo.com
Sun Oct 24 15:14:15 EDT 2004

Oh, by the way -- you can see the 8170 jump when phase lock is lost at 
http://www.febo.com/stats/ntp -- scrolling down through the graphs will 
show you the current day plus two previous days of offset information 
via ntp.  I plot performance of my two Z3801As as well as the 8170.


John Ackermann N8UR wrote:
> Brooke Clarke wrote:
>> Hi John:
>> Is the idea to be able to decode the WWVB time signal by using a known 
>> frequency?
>> Do you have docs on the 8170?
>> Have Fun,
>> Brooke Clarke, N6GCE
> If I understand the docs correctly (I do have a book with schematics), 
> the 8170 derives its master clock from the WWVB carrier, and steers its 
> 1pps off the decoded WWVB timecode.  The microprocessor will advance or 
> retard the 1pps in either 1ms or 100us steps to bring it in alignment 
> with WWVB's second tick.
> When the receiver loses lock (which seems to happen every couple of days 
> due to diurnal effects) and the crystal free-runs, the time will jump by 
> a few milliseconds and it takes quite a while for it to get back in 
> step.  (My guess is that the resting frequency of the crystal when it's 
> out of lock is far enough off 10.000MHz to cause a sudden jump, which is 
> then corrected when lock returns a few minutes later.  But getting the 
> time synchronization back takes quite a bit longer due to the long time 
> constant of its loop.)
> My thinking is to replace the 10MHz phase-locked signal with a local 
> one, and then have just the time-setting PLL at work.  If the WWVB 
> signal is lost, the thing won't jump due to the frequency change.  Of 
> course, doing this loses the ability to correct for errors beyond a few 
> milliseconds, but given the stability and low offset of the Rb, that 
> shouldn't be a real problem.
> Spectracom had an option to automatically switch to an external 
> reference when lock is lost, and I could just duplicate that circuitry, 
> but I'm wondering if, given the availability of the high quality local 
> reference, it's worth doing the switching, rather than just running on 
> the Rb all the time.
> John

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