[time-nuts] Analog or Digital GPSDO?

[WarrenS]

>Q) Can you explain again why you are thinking this? 

A) Yes, Short answer is I do not think Tom's graph's have finished analyzing the data.
As soon as I can get a copy of the raw data so that I can check out my claims in a simulator, I'll show you why I say that.

WarrenS

********************
----- Original Message ----- 
From: "Ulrich Bangert" <df6jb at ulrich-bangert.de>
To: "'Discussion of precise time and frequency measurement'" <time-nuts at febo.com>
Sent: Saturday, December 06, 2008 9:23 AM
Subject: Re: [time-nuts] Analog or Digital GPSDO?


> 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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