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There are a number of situations where the traditional approach to providing precise time and frequency references is not suitable for the local environmental requirements.
The attached paper describes an architecture designed to provide precision timing and frequency references inside a secure area that has no direct access to any external references.
The type of facility where this critical capability is required is, for example, a secure laboratory, or testing facility which is fully enclosed (possibly underground, in a bunker etc.) and where there is no external access permitted.
In this case the traditional approach (typically utilizing satellite receivers receiving signals by means of an antenna with a clear view of the sky) will not suffice, and a more comprehensive approach is required.
What does 10ns Mean Anyway – 1 needle in an 18ft high Haystack!
ptf has just completed development work on a precision clock, synchronized to UTC with a precision of better than 10ns (one sigma standard deviation = 6.86 ns).
To put this into perspective we used an analogy developed by Justin Dolske, Ohio State University, Columbus, Ohio, to compare the difficulty of finding one key out of all the possible variations in the 56-bit DES encryption key.
Dolske calculated that the probability was about the same as finding the proverbial needle in a 1 mile high haystack.
Using the same analogy, we have calculated that the accuracy of a 10 ns clock is approximately the same ratio to one second as finding a needle in an 18ft foot high haystack. Maybe not quite as challenging as the 56 bit DES example, but nevertheless still quite impressive!
To see how its done, download the paper.