[LinuxPPS] DCF77-PPS

[Remco den Besten]

> I think that +-1ms is about as much as you can expect from this type of 
> setup.
> I think that there is some variation in the propagation delay because of
> variability in the propagation path.  I would think that since DCF77 and 
> WWVB
> propagate via ground waves that this should give better results than using 
> HF
> time broadcasts like the 10MHz, 15Mhz or 20Mhz WWVA or WWVH signals since 
> the
> propagation path will be more consistent.  I read some where that using 
> WWVA
> or WWVH about the best you could do was around +-20ms.

Correct. Therefore I am happy to have reached the boundaries of precision 
concerning
this type of reference :-)

> In fact the frequency curves are basically inverted which is something I 
> would
> not expect.   The other thing that is inverted is the direction of the
> frequency correction.

I tried to find out what you meant, but what do you mean with
'basically inverted' ?

> The oscillator on ntp2.remco.org appears to be the most stable of the lot. 
> Is
> this because the room temperature is more stable where it is located or is
> this because this machine happens to have an oscillator that is not as
> temperature sensitive?  In any case I suspect that this machine will give 
> very
> good results with the OnCore GPS.

It is an old machine with a 'pit' (as far as I could ascertain it is a 
hardware timer, related to
the system clock (mostly 14.31818 MHz divided bij 12)) timer. So, indeed I 
am curious
how this machine behaves with a GPS-locked PPS. The machine is located in 
another location
by the way. We'll find out (hopefully) this weekend :-)

> The lithium frequency curve is very similar to freebsd.   Are these 
> located in
> the same room?

Yes, helium, lithium and freebsd are in the same room.
For the 'FreeBSD machine': with the same hardware, using LinuxPPS, I got 
similar plots like helium. The same hardware,
using 'FreeBSD-PPS', yields a more stable and smooth result.

Linux apperantly has another PLL-concept than FreeBSD.

I was even thinking of building a machine with Linux 2.4 and the 'old' 
PPSkit to see how it behaves.

Or.. on other words: what to do to not only have the flags 2001 while 
syncing, but 2107, like FreeBSD
or the PPS-kit?

remco at helium [/home/remco]> ntpdc -c kern
pll offset:           -1.5981e-06 s
pll frequency:        18.051 ppm
maximum error:        0.002751 s
estimated error:      1e-06 s
status:               2001  pll nano
pll time constant:    4
precision:            1e-09 s
frequency tolerance:  500 ppm
remco at helium [/home/remco]> ntpdc -c kern freebsd
pll offset:           1.568e-07 s
pll frequency:        -52.625 ppm
maximum error:        0.00324 s
estimated error:      2e-06 s
status:               2107  pll ppsfreq ppstime ppssignal nano
pll time constant:    4
precision:            1e-09 s
frequency tolerance:  496 ppm
pps frequency:        -52.625 ppm
pps stability:        0.012 ppm
pps jitter:           1.356e-06 s
calibration interval: 256 s
calibration cycles:   48319
jitter exceeded:      76374
stability exceeded:   0
calibration errors:   318
remco at helium [/home/remco]>