[time-nuts] Analog or Digital GPSDO?

[Ulrich Bangert]

Warren,

I may be teriible wrong but I understand Tom and his data so that PPS
and 100 Hz have the SAME performance (what I had expected) with the PPS
being able to be improved by the sawtooth correction. Attached are some
seconds of data from my GPSDO which second Tom's measurements as far as
the PPS is concerned.

> All else being equal, Tom's data says to me that a simple analog front
end design when 
> combined with a microprocessor  is able to provide a better performing
GPSDO 
> than any digital only unit that is using just the 1PPS.

Can you explain again why you are thinking this? Tom's claim is:

For all tau beyond 1 second, the ADEV of the 100 Hz output exactly
matches the ADEV of the 1PPS output.

So, it does not matter whether PPS or 100 Hz are used, it is a question
of the loop time constant only, which must be the same for both.

Best regards
Ulrich

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von WarrenS
> Gesendet: Samstag, 6. Dezember 2008 15:57
> An: Discussion of precise time and frequency measurement
> Betreff: [time-nuts] Analog or Digital GPSDO?
> 
> 
> 
> Here is a posting meant to start a debate between open minded 
> freq-nuts. It is inspired by  Tom's latest posting  at 
http://www.leapsecond.com/pages/m12-adev/

All else being equal, Tom's data says to me that a simple analog front
end design when 
combined with a microprocessor  is able to provide a better performing
GPSDO 
than any digital only unit that is using just the 1PPS. 
It would appear that the analog front end can be as good and even better

than using the sawtooth correction data.

I may be a bit pregidous toward analog because I have been using 
analog only sub ns tracking of the GPS error signal for a long time.

What analog or digital can not address is any of  the issues concerning
non carrier phase receiver limitations. 
so I'd like to assume for this discussion that the GPSDO is using a
Motorola Oncore type 
of receiver with position hold capability.

A different but related question is, does or would using some form of
waas help a GPSDO?

Have fun with it,
WarrenS



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