On 2013-08-27 13:35, Florian Teply wrote:
No, HP did not make the long tube Cs standards at NIST (as the NIST guys always love to point out) and they are very different animals than the ones you can buy. So, the international definition of the second has always been safe from manufacturer induced common mode.
I vaguely remember the NIST guys wanting to copy some of the HP electronics from the 5071A. So don't be so sure. Regarding common mode environmental drift: When the 5071A was introduced, an extensive set of tests was performed over the better part of a year to determine common mode environmental drift. The measurements were sensitive to parts in 10^15. No environmental sensitivity whatsoever was measurable. This was no accident, but rather the result of careful design. OTOH, the 5061 could change frequency noticeably by just removing the top cover. Whatever the merits of the big iron Cs standards, the fact of the matter is that after the 5071A was introduced and they got into circulation, as a group, they accounted for upwards of 80% of the weight of the TAI. Rick Karlquist N6RK _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
