[time-nuts] CW12-TIM vs M12M and the world

Ulrich Bangert df6jb at ulrich-bangert.de
Sat Mar 31 12:57:11 UTC 2012


Gentlemen,

i have to correct myself: The pre-filter's time constant is 1/6 of the pll
time constant and not 1/3 as i stated before. Sorry for that!

Best regards
Ulrich Bangert

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Ulrich Bangert
> Gesendet: Samstag, 31. Marz 2012 14:49
> An: 'Discussion of precise time and frequency measurement'
> Betreff: Re: [time-nuts] CW12-TIM vs M12M and the world
> 
> 
> Bert,
> 
> sometimes a manual can be a true treasure chest! Just 
> download the PRS-10 manual at
> 
> http://www.thinksrs.com/downloads/PDFs/Manuals/PRS10m.pdf
> 
> and find starting on page 13 the complete instructions on how 
> to build your own GPSDO. A basic knowledge of math, 
> programming and control theory is needed to understand the 
> manual but then: It works. I have constructed my mown DIY 
> GPSDO on the base of the information that I have found there, 
> including the pre-filter.
> 
> Best regards
> Ulrich 
> 
> > -----Ursprungliche Nachricht-----
> > Von: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] Im Auftrag von EWKehren at aol.com
> > Gesendet: Samstag, 31. Marz 2012 13:46
> > An: time-nuts at febo.com
> > Betreff: Re: [time-nuts] CW12-TIM vs M12M and the world
> > 
> > 
> > Ulrich
> > can you tell us more about your pre filter?
> > Thank you
> > Bert Kehren
> >  
> >  
> > In a message dated 3/31/2012 6:23:49 A.M. Eastern Daylight Time,
> > df6jb at ulrich-bangert.de writes:
> > 
> > Thomas,
> > 
> > > Has anyone compared the M12M to the  M12+?
> > 
> > I have done some measurements on the M12+ with typical
> > results as  shown in
> > 
> > http://www.ulrich-bangert.de/M12Performance.jpg
> > 
> > The red  line is the raw phase data of the M12's PPS against
> > a PPS derived from a  local FRK-L rubidium. Note that you do 
> > not observe an overall difference  frequency (and a resulting 
> > drift in phase) because the FRK-L is disciplined  by the GPS. 
> > The blue line is the sawtooth corrected phase data and it  
> > becomes immediatly clear HOW IMPORTANT applying the 
> > correction is. The  yellow line show you what happens if the 
> > sawtooth corrected phase data is  sent through a pre-filter 
> > (lowpass with 1/3 the time constant of the  
> > main
> > pll loop) before entering the loop itself. That is something 
> > that I  learned from the PRS-10 manual. You may decide on 
> > your own which data you  would 
> > like
> > to work on in a GPSDO.
> > 
> > Best regards
> > Ulrich Bangert
> > 
> > > -----Ursprungliche Nachricht-----
> > > Von:  time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] 
> > > Im  Auftrag von Tom Knox
> > > Gesendet: Freitag, 30. Marz 2012 22:19
> > >  An: Time-Nuts
> > > Betreff: Re: [time-nuts] CW12-TIM vs M12M and the  world
> > > 
> > > 
> > > 
> > > Has anyone compared the M12M to the  M12+?
> > > Thanks for all the input, it is really appreciated.
> > > best  wishes;
> > > Thomas Knox
> > > 
> > > 
> > > 
> > > > CC:  time-nuts at febo.com
> > > > From: saidjack at aol.com
> > > > Date: Fri,  30 Mar 2012 09:53:17 -0700
> > > > To: time-nuts at febo.com
> > > >  Subject: Re: [time-nuts] CW12-TIM vs M12M and the world
> > > > 
> > >  > Hello Ed, Azelio,
> > > > 
> > > > We should also compare the  same parameters. Sawtooth error
> > > of the m12+
> > > > of +/-25ns  is not its standard deviation, it's max/min.
> > > Compare that
> > >  > number to your 30ns max/min measurement on the 5372a.
> > > >  
> > > > Standard deviation of the m12+ is around 2ns with
> > correction.  That
> > > > needs to be compared to the 5ns you measure on the 5372a
> > as  that is
> > > > the best performance you will get from the CW12. Yes the
> > > uncorrected
> > > > 1pps of the m12 is worse, but it is  designed to be used with 
> > > > correction. So in the end the m12m  still performs better
> > than the
> > > > CW12.
> > > > 
> > > >  Bye,
> > > > Said
> > > > 
> > > > Sent From iPhone
> > >  >
> > > > On Mar 29, 2012, at 1:56, Azelio Boriani
> > <azelio.boriani at screen.it>
> > > > wrote:
> > > > 
> > >  > > We (that is my company) use the CW12-TIM (NMEA version) and  
> > > its PPS
> > > > > wonders as usual, nothing different from a uBlox  LEA-5T
> > > or the M12M.
> > > > > 
> > > > > On Thu, Mar  29, 2012 at 9:32 AM, Hal Murray  
> > > > > <hmurray at megapathdsl.net> wrote:
> > > > > 
> > > >  >>
> > > > >>>> The sawtooth error on the Motorola  M12+ is about +/-
> > > 25ns, while
> > > > >>>> the  CW12-TIM has a sawtooth error of +/- 2 ns, so
> > > correcting for
> > >  > >>>> the sawtooth error is not as critical with the  CW12-TIM.
> > > > >> 
> > > > >>> The first  claim
> > > > >>>> The sawtooth error on the Motorola M12+ is  about +/- 25ns
> > > > >>> is correct but are you absolutely  sure that the
> > second claim is
> > > > >>> correct  too?????
> > > > >> 
> > > > >>> It would mean a  factor >10 improvement of the CW12-TIM
> > > against the
> > > >  >>> M12
> > > > >> which
> > > > >>> is  hardly believeable.
> > > > >> 
> > > > >> The 25 ns  probably comes from period of the the free
> > > running clock
> > >  > >> they are using.  It doesn't seem unreasonable to me
> > to get  10x
> > > > >> better if they use a GPSDO for the local clock so  they
> > > can get the
> > > > >> PPS edge right where they  want it.
> > > > >> 
> > > > >> 
> > > > >>  
> > > > >> --
> > > > >> These are my opinions, not  necessarily my employer's.  I
> > > hate spam.
> > > > >>  
> > > > >> 
> > > > >> 
> > > > >> 
> > >  > >> _______________________________________________
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