[ntp:questions] Re: WWVB 60kHz Receiver
hmurray at suespammers.org
Sat Apr 15 06:43:19 UTC 2006
>The reason I ask is I'd like to set up a refclock at my employer's HQ,
>but the datacenter is in the 10th floor of a 50-floor high rise. The
>building is closely surrounded by others with similar or greater
>height. I can't use GPS becuase none of the windows open, renting roof
>space is not possible, and I cannot get any GPS signal through the
>windows. The location is basically the worst "urban canyon" scenario
>you can imagine .
>I'm 1462.5 km (4.8 ms) from the WWVB transmitters, which is well inside
>the coverage area maps on the NIST site. I figure WWVB is my best
>(only?) option for a refclock at this location. Is sub-milisecond
>accuracy possible using a WWVB refclock? The NIST site says 0.1 to 15
>ms phase error, which is two orders of magnitude. I see ~5 ms average
>offsets when I sync with nearby stratum-1 servers via NTP. Would WWVB
>perform any better?
I'm not a wizard on this topic.
I think WWVB has significant variation on propagation delays over
the day. You can probably get good accuracy if you have a good
crystal and are willing to average over a week or so.
I don't know of any box that does that. The normal PC crystal
is not very good on this scale so you can't do the averaging
from withing NTP. At least not if you NTP server is in a house
like mine. Maybe you can if you have good air conditioning.
Do cell phones work in your offices? If so, there is at least
one company making NTP boxes that work off cell phone timing which
is basically a relay from GPS.
Google for >CDMA NTP<. This is the one that I remember:
(I have no idea if their gear is any good. It's out of my
hobby price range.)
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