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

Ulrich Bangert df6jb at ulrich-bangert.de
Sat Mar 31 10:19:38 UTC 2012


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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