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

EWKehren at aol.com EWKehren at aol.com
Sat Mar 31 11:46:07 UTC 2012


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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