Hey Gary, On Mon, 31 Dec 2018 at 05:02, Gary E. Miller <gem@rellim.com> wrote:
The Rb frequency reference will be two or three orders of magnitude more stable than an expensive ovenized crystal.
Perhaps, but not supported by this: https://www.meinbergglobal.com/english/specs/gpsopt.htm For the tl;dr folk, crystal drifts +-4.5us per day, Rb +-1.1us (both seem like unsatisfactorily high numbers to me, i.e. you don't want to be free-running 24h with Rb). Luckily today we have GPS, Glonass, BeiDou, Galileo and couple smaller ones, so there should be somewhat reasonable amount of redundancy. Unsure which commercially available NTP or PPP master clocks support all four. But I of course readily accept Rb is objectively more accurate than crystal, I'm just curious where it matters and I'm curious which regulation applies, who fall under the regulation and what specifically does the regulation require about free-running accuracy. -- ++ytti