[time-nuts] Re: Question about GPS 1PPS ADEV

[John Ackermann]

Private email from the folks at NRCan indicated that having both constellations in the data would potentially result in (more) clock offset jumps in the PPP results.  Remember that GLONASS and GPS are synced to different master clocks which are some small (and potentially variable) number of nanoseconds apart.  But part of it may also be that their modeling of GLONASS clocks and orbitals isn't as robust as for GPS due to having less experience with it.

If you're purely interested in location, multiple constellations can be helpful, but the precision timing application is a bit different. 

Also, note that this is probably a non-issue for simple non-post-processed GPS PPS, as the other error sources would swamp any timescale differences.

John

On Apr 21, 2022, 12:09 PM, at 12:09 PM, Markus Kleinhenz via time-nuts <time-nuts at lists.febo.com> wrote:
>Hello Matthias,
>
>> Of course curiosity got the better of me. I switched the GPSDO to
>hold-over 
>> and recorded about 4000 seconds of data. Result is attached. BTW I
>terminated 
>> the experiment after the temperature compensation kicked the DAC one
>LSB down. 
>> I am quite pleased with the performance of the OCXO, though. I was
>not 
>> expecting that, it is really nothing special. Not a surplus Chinesium
>OCXO, 
>> but something you can buy for quite reasonable money from Digikey.
>>
>> So, the bulge is getting a bit more prominent, but it is in no way as
>
>> prominent as the figure 26 in John Ackermann's paper. 
>>
>> John, what constellations did you have enabled during the test? Just
>GPS, or 
>> also others? I usually run with GPS and Galileo enabled (and I avoid
>GLONASS, 
>> it messes everything up). Can this make a difference?
>>
>>
>Could you explain further how enabled GLONASS messed things up for you?
>
>Regards,
>
>Markus
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