[time-nuts] GPS for Spirent Smartbits

Brian Kirby kirbybq at bellsouth.net
Fri Feb 16 18:53:50 EST 2007

Do not know if this will help, but the older Motorola Oncore Basic, XT 
and VP can output 1 PPS timing while in the navigation mode and its 
stated at 130 nS with SA on.  Then its rated at less than 50 nS in 
position hold with SA on.

Brian - N4FMN

Hal Murray wrote:
>> I have been thinking about this... It will no work,  as GPS needs to
>> be in position hold which is not compatible to mobility.... We will
>> think about connecting via 3G to an NTP server... and make some tests
>> to see if results have any sense... 
> There are two types of software for GPS receivers: timing and navigation.  
> (There is probably another one for surveying.)
> The low cost units are intended for navigation.  They don't have a position 
> hold mode.
> I'm pretty sure the Garmin GPS-18-LVC I suggested doesn't have a position 
> hold mode.  (If it does, somebody please send me a clue.)
> You could also try letting your NTP server run without any clock.  Look at 
> the documentation for the local refclock.  It will have some offset and some 
> drift, but you can correct for that if you can get good data before and after 
> a set of tests.
> I'm assuming the links will be unloaded when you aren't testing.  That may 
> not be true.  Or maybe you just have to work a bit harder to get some 
> calibration data.
> I'm also assuming the temperature is stable and the test doesn't run too long.

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