[time-nuts] comparing two clocks
jimmydburr at gmail.com
Sat Feb 22 08:17:00 EST 2014
I need some help with a 'noob' question regarding some practical examples in some of the NIST literature. When attempting to compare two clocks, I'm a bit confused on the subject of exactly how to use my counter to compare a delayed clock relative to another. Or perhaps I should just say 'comparing two clocks'. Let's take some concrete examples.
Let's say I want to characterize my Morion MV89 ocxo using my HP5335a. Obviously, I can tune the MV89's 10MHz by +/- 1Hz and feed it to the counter's input 'A'. Obviously, I can feed in a second, external reference clock at 10MHz into input 'B'. Suppose, however, I didn't have an external reference clock. Can I compare against the counter's internal time base by hooking a line from the rear jack time base output to channel 'B' input? Or am I making it too complicated? Do I simply plug into input 'A' and go?
In a somewhat related question, in this article (http://www.wriley.com/Examples%20of%201%20PPS%20Clock%20Measuring%20Systems.pdf) where two clocks, both divided to 1PPS, were compared, W.Riley makes the following statement, "The two 1 PPS outputs were connected to a Racal Dana 1992 time internal counter having 1 nanosecond resolution, and the start and stop signals were separated sufficiently in time for the counter to function properly". I wonder what exactly is meant by "separated sufficiently in time for the counter to function properly" and how one would go about doing this? For example, is inverting one of the signals sufficient separation? If not, how is this typically done? Delay line?
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