[ntp:questions] Ultralink 325 WWVB receiver

Dennis Hilberg, Jr. timekeeper at dennishilberg.com.invalid
Sun Feb 17 06:49:29 UTC 2008

Rob Kimberley wrote:
> Interesting plots! Have tried to make some sense of them, but rather 
> difficult.
> 1) How is the Rx powered? (I don't know the product)

It's powered from the RS232 connection currently.  It also has an external 
5V DC power supply that can be used instead.

> 2) Do you know what type of oscillator is used in the Rx, and how it is 
> supposed to be controlled?

The only thing I could find regarding that in the user's manual is this 
brief statement:

"A microcomputer processes WWVB signals, maintains an accurate real time 
clock and hosts the serial communication interface. Received data is 
correlated over time to set an internal real-time clock (RTC). The RTC is 
driven by a precision quartz crystal for continuous accurate time reference."

> 3) The changes in offset don't appear to follow any regular 24 hour pattern, 
> so would tend to rule out diurnal effects, plus the changes are much larger 
> than one would expect.

I haven't ruled out the possibility of interference yet. Although, according 
to my clockstats file, it gets an R5 signal (R1 being unreadable signal and 
R5 the best) a large portion of the time. In fact the clockstats file for 
the 16th of Feb. showed R2 - R5 about 85 percent of the time. Is it possible 
that even though the signal is strong some interference is affecting the 
unit's accuracy?

> I notice a large step around 02:00 on a Saturday. 
> Does anything large get switched off/on at this time? Thinking along the 
> lines of some sort of power surge causing interference to the receiver.

Normally my Windows machine shuts down via the Task Scheduler at 2am every 
day, after some backups take place. But this last time the machine running 
the WWVB receiver (apollo) restarted somehow shortly after that time. I 
don't know what happened as /var/log/messages doesn't show anything.

The odd thing about the WWVB receiver is the initial offset on an ntpd 
restart is not consistent and ntpd pretty quickly declares it a falseticker. 
I have to manually fudge the time1 setting with ntpdc, otherwise it will 
stay a falseticker.

Anyway, that's why the offset converged real close to zero early Saturday 
morning, as you can see on the janus graph, as ntpd declared the WWVB 
receiver a falseticker after the reboot, and synced to saturn (the machine 
running the GPS reference), which janus (the observation machine) is also 
synced to.

> More later (and apologies for the delay in replying)

No worries, I'm thankful for any assistance.

> Rob Kimberley


Dennis Hilberg, Jr.     \  timekeeper(at)dennishilberg(dot)com
NTP Server Information:  \  http://saturn.dennishilberg.com/ntp.php

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