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

Brian, WA1ZMS wa1zms at att.net
Fri May 4 00:01:44 UTC 2012


All good points, and all very true.

I often remind myself of how over simplified sometimes people view things.
Case in point:
I once had a high level manager hold an all employee meeting in which he
started his talk by saying that
"Nothing difficult is ever easy."   Needless to say.......he didn't last
long in his job and left the company.

-Brian, WA1ZMS


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bob Camp
Sent: Thursday, May 03, 2012 7:42 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Interesting paper: Don't GPSD' your Rb...

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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