[time-nuts] GPS: ADEV or MDEV?

Didier Juges didier at cox.net
Fri Apr 13 07:53:47 EDT 2007


Dr Bruce Griffiths wrote:
>
> Peter
>
> I only intended to indicate that not all GPS timing receivers need 
> exhibit hanging bridges.
> The Trimble Resolution T for example may (or may not) exhibit hanging 
> bridges.
> If anyone has any evidence either way it would be interesting to look at it.
> If one also logs the PPS correction then you haven't lost any 
> information due to the randomisation of the PPS error.
>
> Surely its better to detect the pseudorange instability in software (if 
> one has access)  rather than attenuating the signal from all SVs.
> Another option is to use multiple GPS antennae operating as a phased array.
>
> Bruce
>
>   
I believe the Thunderbolt should not exhibit hanging bridges either, 
since it's OCXO is used to clock the CPU.
I have yet to demonstrate that.
It would be helpful to have another GPSDO design to compare it against, 
and I have not come around to finishing my own home-brew design yet.

The interesting part is that the Thunderbolt is actually a simpler 
system. Hanging bridges are due to the beat (or lack thereof leading to 
a constant phase offset) between the OCXO and the CPU clock if I 
understood well. If these two are one and the same, the problem goes away.


Didier




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