Hi, I'm in the process of setting up a public stratum 1 NTP server which
will have at least one standard as a fallback to GPS (and possibly WWV
and CHU), in addition to its primary purpose as a timebase for a
microwave active SETI transmitter. So far I have an aging = 1E-11
rubidium standard (which has expired calibration documentation), and I'm
interested in adding more standards in the future, specifically
high-quality OCXO(s) and additional rubidium standard(s) (I'm
uninterested in cesium standards due to their definite and short
lifespan, and masers are, in almost all certainty, insanely expensive).
Based on attempts of understanding the NTP documentation and answers
from NTP fora, NTP doesn't perform PPS fusion for accuracy, but rather
merely for redundancy (correct me if I'm wrong). Therefore, this
complicates things to an extreme degree, for it means that the RF
outputs (typically 100 kHz, 1 MHz, 5 Mhz, and/or 10 MHz), or PPS outputs
have to be combined using some sort of a weighted fusion method (or
simply unweighted, if the aging figures are similar across all the
standards). The only commercial piece of equipment to perform this,
manufactured by some Russian corporation, is obscure and just by the
look of it prohibitively-expensive. So that leaves custom fabrication;
the best information I could find regarding this is the paper ``A
Digital Technique for Combining Frequency Standards'', by Lynn Hawkey,
published in '69, which outlines nonnovel approaches and a novel
approach to fusion. The method that's attractive to myself is the old
RF mixing one, wherein double-balanced mixer(s) are used to sum RF
signals from standards of similar aging figures, the resulting output(s)
filtered, and the output finally sent to a frequency divider to generate
the desired final RF signal (like 1 MHz for typical time code
generators). Any ideas?
Thanks in advance,
Ruslan
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