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

[Azelio Boriani]

Yes, me too was interested in what kind of filtering is going on.
Thank you

On Sat, Mar 31, 2012 at 1:46 PM, <EWKehren at aol.com> wrote:

> 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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