[time-nuts] Interesting paper: Don't GPSD' your Rb...

[Bob Camp]

Hi

If you dig into commercial GPSDRb's their loop time constants are *very* long. They crank out to a couple days fairly quickly. In addition they (like a lot of GPSDO's) have lowpass filters in the loop in addition to the basic PLL /  FLL structure.

Bob

On May 3, 2012, at 6:30 PM, Azelio Boriani wrote:

> And maybe the problem is worse: I want also to keep aligned the PPS. To
> recover the PPS position (without phase jumps) it is mandatory to slightly
> force the 10MHz. Better start the machine and take measures...
> 
> On Fri, May 4, 2012 at 12:20 AM, Brian, WA1ZMS <wa1zms at att.net> wrote:
> 
>> At the risk of over simplifying it: Doesn't it all always depend on the
>> loop
>> BW you pick?
>> 
>> Inside the loop BW you see the noise of the loop's reference. Outside the
>> loop BW you see the free running noise of the oscillator.
>> At and around the loop's corner frequency you see a combination of both.
>> The choice of loop BW depends on what Tau you want
>> and what grade of Rb you are trying to improve.
>> 
>> But as PHK said, the article was a bit thin on details.
>> 
>> 
>> -Brian, WA1ZMS
>> 
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Azelio Boriani
>> Sent: Thursday, May 03, 2012 6:06 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Interesting paper: Don't GPSD' your Rb...
>> 
>> OK, I've read the paper. Why not GPSDiscipline your Rb? GPSDiscipline "cum
>> grano salis" but do it. My LPFRS GPS disciplinator hardware is ready. OK, I
>> know, the 1E-11 step is too large but I'll try. First I'll take
>> measurements
>> so that I can think about a disciplining algorithm. Then a hardware
>> modification on the LPFRS to get access to the C-field could make it
>> better.
>> 
>> On Thu, May 3, 2012 at 11:29 PM, Poul-Henning Kamp
>> <phk at phk.freebsd.dk>wrote:
>> 
>>> 
>>> This is pretty think, but interesting:
>>> 
>>> http://tf.nist.gov/sim/Papers/Trigo_CPEM_2010.pdf
>>> 
>>> --
>>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>>> FreeBSD committer       | BSD since 4.3-tahoe
>>> Never attribute to malice what can adequately be explained by
>> incompetence.
>>> 
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