[ntp:questions] Re: Basic MSF clock setup

Chris Hastie chris at nospam.oak-wood.co.uk
Wed Nov 12 09:05:25 UTC 2003

In message <dbiqob.b78.ln at>, Jonathan Buzzard
<jonathan at uk.me.buzzard> writes
>In article <aUsd88HVdKs$EwnR at nospam.oak-wood.co.uk>,
>       Chris Hastie <chris at nospam.oak-wood.co.uk> writes:
>> It strikes my that it shouldn't be too difficult to adapt the GENERIC
>> driver for raw MSF, based on the existing raw DCF mode. Would there be
>> any advantage to doing this over using radioclkd2 and the SHM driver?
>There would be little or possibly negative advantage in doing so.

Fair enough

>> The other thing I'm wondering about is PPS.
>The best bet is to do some time pulse clock averaging in the SHM driver.
>It improves jitter by an order of magnitude. Consider it a poor
>man's PPS.

I'm not clear what this means. I presume its something that should be
done in radioclkd*, or is it a configuration option for the SHM
reference clock in ntp?

As far as I can make out, radioclkd2, which I'm using as I failed to get
radioclkd to compile on FreeBSD yet, includes such averaging. Never the
less, using the PPS driver as well does seem to improve clock stability,
at least it reduces the mean offset and jitter relative to the SHM
clock. I'm giving it a day or so in various configurations to try to
work out which is best - though it would probably help if I properly
understood all these numbers :) Are there features of radioclkd not
present in radioclkd2 that mean I should be trying harder to figure out
how to get it to compile on FreeBSD?

> If you really have need for PPS then you should use
>a GPS unit.

I don't. I'm just trying to leverage the most I can out of £30 worth of
bits blu-tacked to my window ledge and take advantage of living 30Km
from the MSF transmitter.

>Remember the philosophy behind my radioclock is to have
>really simple physical hardware with smart software to deliver a
>previously unobtainable simplicity/price/performance ratio. It
>does not attempt to rival the accuracy of a GPS unit, though it
>can make for a dirt cheap backup time source.

Many thanks for putting the details up.

Chris Hastie

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