Frequency Reference for NTP Use?

Alex Satrapa grail at
Sun Jul 14 00:27:20 EST 2002

On Saturday, July 13, 2002, at 10:06 , Brad Hards wrote:

> A few seconds a month is probably going to require some kind of 
> temperature
> stabilisation.

When you move from temperature compensated oscillators to ovenised* 
oscillators, you move from 1 second/week to about 1 second/year 
stability.  You also move from the order of $x00 to $x000.

> Unless you are really concerned with GPS availability, I'd look for
> a GPS with a 1PPS output.

The catch is that such units are usually designed to be rack mounted, 
and they're usually in the order of $1500.  My budget is significantly 
less than that.

I'll probably try to read through the NMEA driver to figure out where it 
gets the second-edge from, and find some way of reducing the jitter - 
such as the first character in the stream, rather than the first 
character of the time stamp.

The least expensive ovenised oscillator with 1PPS output I could find is 
about $4,500.

According to the NTP server, the jitter on the processor clocks of my 
Pentiums is about 0.008ms.  That may actually do for the meantime.

* When I first read through the xntpd documentation, I read this as 
oven-sized.  Which isn't that far off, when you see the setups that some 
places have for their Campus' Master Clock.
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