[time-nuts] standard fusion for accuracy and redundancy

[Ruslan Nabioullin]

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