Hi On some counters, if both inputs arrive at exactly the same time, they get very confused. The normal approach is to offset one by a few hundred ns or so. The exact offset is fairly non-critical. It’s real value depends entirely on the amount of drift you expect to see over the time period you are checking.
If your oscillators are off by 1 ppm, they will slip by 1 us per second. If you want to check them for 12 days or more you will need an offset of more than one second. If they are off by 1 ppb, then your offset could be a bit over one millisecond to handle a 12 day run. (12 days is roughly 1 million seconds). Bob On Feb 22, 2014, at 8:17 AM, Jimmy Burrell <jimmydb...@gmail.com> wrote: > 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? > > Thank you, > > Jim... > N5SPE > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
