Ask Bjørn Hansen
ask at develooper.com
Wed May 1 23:43:20 UTC 2019
> On May 1, 2019, at 12:22, Mehmet Akcin <mehmet at akcin.net> wrote:
> I am trying to buy a GPS based NTP server like this one
> but I will be placing this inside a data center, do these need an actual view of a sky to be able to get signal or will they work fine inside a data center building? if you have any other hardware requirements to be able to provide stable time service for hundreds of customers, please let me know.
[ with my hobby-hat on … ]
tl;dr: if any of the below is too much work, just run reasonably well monitored NTP server syncing from other NTP servers. If you want more than that, you need to see the sky. Don’t do the CDMA thing.
Depending on your requirements having the antenna in the window may or may not be satisfactory. If it’s fine you probably could just have done a regular NTP server in the first place. For long swaths of the day you might not see too many satellites which will add to the uncertainty of the signal.
Meinberg’s GPS antenna has a bit more smarts which helps it work on up to 300 meters on RG58 or 700 meters on RG213. (They also have products that use regular L1 antennas with the limitations Bryan mentioned).
They also have a multi-mode fiber box to have the antenna be up to 2km from the box or 20km with their single mode fiber box, if you have fiber to somewhere else where you can see the sky and place an antenna.
It will be more than the one you linked to, but their systems are very reasonably priced, too. For “hundreds of customers” whatever is the smallest/cheapest box they have will work fine. Even their smallest models have decent oscillators (for keeping the ticks accurate between GPS signals).
The Meinberg time server products (I am guessing all of them, but I’m not sure) also have a mode where they poll an upstream NTP server aggressively and then steer the oscillator after it. I haven’t used it in production, but it worked a lot better than it sounded like it would. (In other words, even without GPS it’s a better time server than most systems).
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