[ntp:questions] Re: Why is my GPS source being marked as a falseticker?

Richard B. Gilbert rgilbert88 at comcast.net
Sat Mar 5 13:06:17 UTC 2005


joe at via.net wrote:

>ntpq> peer
>     remote           refid      st t when poll reach   delay   offset
>jitter
>==============================================================================
>xGPS_PALISADE(0) .GPS.            0 l    8   16  377    0.000  122.963
> 0.791
>xtime.sdsc.edu   .WWVB.           1 u   36   64  377   17.366  698.468
>83.650
>*time.nist.gov   .ACTS.           1 u   31   64  377   26.225  625.921
>58.752
>+father-time.t-b .GPS.            1 u   35   64  377   54.071  570.338
>84.208
>+clock.isc.org   204.123.2.5      2 u   41   64  377    3.861  559.937
>102.295
>ntpq> op
>     remote           local      st t when poll reach   delay   offset
>  disp
>==============================================================================
>xGPS_PALISADE(0) 127.0.0.1        0 l    2   16  377    0.000  123.676
> 0.315
>xtime.sdsc.edu   209.81.9.7       1 u   48   64  377   17.366  698.468
>83.650
>*time.nist.gov   209.81.9.7       1 u   43   64  377   26.225  625.921
>58.752
>+father-time.t-b 209.81.9.7       1 u   47   64  377   54.071  570.338
>84.208
>+clock.isc.org   209.81.9.7       2 u   53   64  377    3.861  559.937
>102.295
>
>
>Any ideas?
>
>Thanks,
>
>Joe McGuckin
>joe at via.net
>
>  
>
It's pretty clear why ntpd *thinks* it's a falseticker!

Remember that the maximum error in transmitting time from server to 
client is one half of the round trip delay.
Your GPS receiver appears to be in error by about 400 milliseconds!!

You can force ntpd to accept the GPS time by unconfiguring all the 
network servers.   If you can find happiness with a 400 millisecond 
error, by all means do so.  If you want the correct time, fix your GPS 
receiver or replace it with a better one!!!!!

You didn't say what sort of GPS receiver you are using, which driver (if 
there is a choice), what version of ntpd you are using, what hardware 
platform you are using or what O/S you are running on it.   Knowing all 
this might help us to help you.

If you are using a GPS receiver not designed for timing service, you 
will not get nearly the accuracy you could expect from one designed for 
timing.  If the receiver does not generate a PPS signal or if you have 
not configured it, you will have a much greater uncertainty than if you 
had PPS.   Navigational GPS receivers know what time it is but give 
precedence to transmitting positional information.




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