[ntp:questions] GPS-UTC Leap Corrections

Todd Glassey CISM CIFI tglassey at earthlink.net
Tue May 5 15:50:03 UTC 2009

Hal Murray wrote:
> In article <485551ee-a847-45b6-a040-624dc80ce2e2 at s38g2000prg.googlegroups.com>,
>  cjc <yheffen at gmail.com> writes:
>> We have some time servers with GPS clocks. One of their uses is in
>> operations centers where satellites are being flown. The satellites
>> use
>> GPS (as opposed to UTC) internally, so we want the computers on the
>> ground also to use GPS (rather than UTC). The time servers speak NTP
>> and hand out GPS time as if it were UTC. The ground computers think
>> they are on UTC, but it's really GPS.
>> But we'd like some of the computers to really be on UTC. I really
>> haven't
>> been able to think of a good way to have computers use the GPS time
>> given out by the time servers as a source, but then to actually offset
>> their own time by the GPS-UTC difference. Some quick Googling hasn't
>> turned anything up. Anyone have some suggestions on how to manage
>> something like this? Or are we just going to have to live 15 seconds
>> ahead of the rest of the world?
> The GSS satellites also tell you the offset from GPS time to UTC.
> Most of the (low cost) GPS receivers tell you UTC rather than GPS.
> Things get interesting around leap seconds.  Other than that,
> UTC via GPS works pretty well.
> What type of GPS clock/receivers are you using?
I  would also bring up the issues with L1 GPS being so easily spoofed 
from a trust-anchor standpoint L1 is almost worthless - if you need to 
prove the source of the time then you need an AutoKEY based relationship 
with some reliable provider.

Todd Glassey
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