[ntp:questions] PPS from an external OCXO source. Correcting drift is it possible?

John Ackermann N8UR jra at febo.com
Sun May 3 11:44:09 UTC 2009

Kat said the following on 05/03/2009 12:05 AM:
> Nero Imhard wrote:

>    > A much more reasonable approach would be to hook up the OCXO to
> your
>    > computer's hardware clock for better stability.
> Unfortunately not as easy as it seems high frequency clocks are
> notoriously difficult to construct and calibrate and a new custom
> clock or clocks would be needed every time I changed server so I opted
> to do something portable.

I try to avoid shameless plugs, but have you considered the TAPR 
Clock-Block (http://www.tapr.org/kits_clock-block.html)?  It's a clock 
synthesizer specifically designed to allow clocking a PC motherboard 
from an external OCXO (or other high quality) reference.  It'll take 
inputs like 5 or 10 MHz and generate outputs up to a couple of hundred MHz.

I use the Clock-Block to generate 33.333... MHz to drive a Soekris 4501 
single board computer which has some unique hardware timing capabilities 
such that by adding a high quality PPS you end up with an NTP server 
that can keep time to fractions of a microsecond.  I have details of 
that at http://www.febo.com/pages/soekris.*

TAPR is currently out of stock on the Clock-Block, but we are having 
another run made and they should be available Real Soon Now.


* Note -- if you look at the performance plots linked from that page, 
things won't look so good right now -- the Cesium clock that I use as 
the reference for the offset comparisons died and is now acting like an 
OCXO.  Haven't had a chance to reconfigure to switch to the alternate Cs 
source yet.

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