Periodic spike in offset for pps

Doug Curtis doug.curtis at
Tue May 5 19:22:23 UTC 2020

On Tue, May 5, 2020 at 2:51 PM Paul Theodoropoulos via users <
users at> wrote:

> A few things to check, and questions.
> Your temps seem quite consistent - are you using ntpheat or another
> application to try to smooth daily temperature variations? It would be
> unlikely they'd cause dramatic spikes though...
For now, I'm using the bubblewrap mailing envelope case. :)

Only tangentially related  - since only two of the three are using the
> Adafruit gps hat - are you regularly (weekly, biweekly) downloading the
> satellite ephemeris data from mediatek?

I'm not familiar with that so I'll have to do some reading on it.

> The most peculiar characteristic is the 'long wave' rise of positive
> offset spikes followed later by negative offset spikes (specifically the
> 'server offset SHM1' graph). The only thing that it vaguely matches up
> with is the local GPS long wave due to visibility. But again - spikes
> would certainly not be an expected symptom of visibility!
> Are you using a common power supply/source for all three pi's - including
> the ntpviz device?

The ntpviz server is a separate Centos 7 server in my rack on a different
circuit.  Each pi has its own power supply and they are on separate
circuits.  I believe the pi3 and pi4 are using Canakit power supplies.
Because of this testing, each antenna is on a different side of the house
(west, south, and east).  This does start me wondering the cleaniness of my
power at the house though.  Since the spikes don't seem to happen on all of
them at the same 34 minute interval, I'm guessing it's probably not
something noisy on my house power.  I did just receive a pi3 with an office
raspberry pi power supply and once I solder the Adafruit breakout gps kit,
I plan on testing with it as well.

> Pure shots in the dark. I've dealt with intermittent spiking in the long
> ago past, with a resolution that is very unlikely to be related (turning
> off the Monit monitoring application, which isn't part of the default
> install of debian/raspbian)
Thanks for the ideas.  I've just removed the avahi daemon and will check on
the results of that.  I plan to go through and eliminate unneeded services
one by one to try and narrow this down further.

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