[time-nuts] Soekris without a GPS receiver.

Bob Camp kb8tq at n1k.org
Sat Dec 27 11:18:20 EST 2014


You can use a PPS from any “on time” source. The PPS driver is the place to look / thing to use for this. 

The gotcha is that unless the PPS is indeed pulsing at the right time, it will not improve the performance of the NTP client / server on the box. Without something like a GPS / WWVB / DCF77 / Loran-C receiver you have a tough time knowing what is indeed on time. NTP in free run is likely better than 10 ms, so attaching anything less accurate than this will actually make things worse rather than better. In this case it’s accuracy you are after, not stability or repeatability. 

There are a number of cheap GPS gizmos on the auction sites for ~$20 delivered that will take care of your shortage of "timing junk” (my wife’s term for fine timing hardware). For NTP there is no need for a fancy GPSDO, the raw PPS out of a good GPS is better plenty good enough. Be careful using the raw PPS from a GPS that is not designed for timing, it may not be up to the task. Yes there are also more exotic solutions like a free running cesium standard and a clock trip to calibrate it. 


> On Dec 27, 2014, at 4:56 AM, David J Taylor <david-taylor at blueyonder.co.uk> wrote:
> I have a Soekris 4501 running with NanoBSD and have got as far as adding the PPS/DCD/GPIO modifications to the hardware.  NTPns itself is working, and the red LED is flashing as expected.
> I would now like to get NTPns working with that more precise timing which is available, but as I don't have an Oncore or a DCF77 receiver I am stuck.  Is it possible to use just the PPS/DCD line on its own for the fraction of the seconds, or would I need one or other of those receivers to make it work? If it can be made to work, what are suitable configuration commands?
> Thanks,
> David
> -- 
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