[time-nuts] CW12-TIM vs M12M and the world
Azelio Boriani
azelio.boriani at screen.it
Sun Apr 1 16:57:47 UTC 2012
Thank you for sharing your filter implementation. I'll study it.
On Sun, Apr 1, 2012 at 1:42 PM, Ulrich Bangert <df6jb at ulrich-bangert.de>wrote:
> Hello Ernie,
>
> please allow me to correct your use of my first name. It is "Ulrich" and
> not
> "Ulbrich". I attach great importance to this difference because a certain
> Walter Ulbricht was one of the leading politicians in the communist terror
> regime of the former so called "German Democratic Republic" and I do not
> want my name to sound even similar to his one.
>
> > Understand that the key point is the PLL or the phase
> > comparator circuit.........if you want to build you own GPS-DO.....
>
> As far as I remember I had understood this when I started my DIY GPSDO
> project. If you have not read about it yet take it as an indication that I
> did not want to publish it. Nevertheless you can see some pictures of it in
> the photo gallery
>
> http://www.ulrich-bangert.de/html/photo_gallery_1.html
>
> of my homepage.
>
> > can you please be a more specific.... namely to show
> > us the pre filter and other circuit....if you do not mind.
>
> The Pll as well as the pre filter is SOFTWARE and not hardware as your
> question may imply. Again I have to use the P-word because the software was
> written in PASCAL. The pre filter and the PLL part reads like:
>
> procedure ComputePreFilter;
> begin;
> PrefilterValue:=PrefilterValue*PreFilterTimeconstant
> +PhaseDelay*(1-PrefilterTimeConstant);
> Str(PreFilterValue,PreFilterValue_S);
> end;
>
> procedure DoPll;
> var count:integer;
> flag:boolean;
> sum:Extended;
> begin;
> if DoPrefilter then PllPhaseValue:=PrefilterValue else
> PllPhaseValue:=PhaseDelay;
> TimeConstant:=Sqr(NaturalTimeConstant)*(KDet*KVco);
> If NeueZeitKonstante then
> begin;
> NeueZeitKonstante:=False;
> Sum:=PropValue+IntegralValue;
> PropFactor:=2.0*StabilityFactor/Sqrt(KDet*KVco*TimeConstant);
> PropValue:=PropFactor*PLLPhaseValue*1.0E-9*KDet;
> IntegralValue:=Sum-PropValue;
> end;
> PropFactor:=2.0*StabilityFactor/Sqrt(KDet*KVco*TimeConstant);
> PropValue:=PropFactor*PLLPhaseValue*1.0E-9*KDet;
> IntegralValue:=IntegralValue+PllPhaseValue*1.0E-9/TimeConstant*KDet;
> begin;
> TuningWord:=SollTuningWord-(PropValue+Integralvalue)*KVco/PllFactor;
> FiltTuningWord:=(1-0.2)*FiltTuningWord+0.2*TuningWord;
> TuningWord:=FiltTuningWord;
> StoreTuningword:=TuningWord;
> MakeTuningBinary(TuningWord);
> count:=0;
> repeat
> SetFrequency_9852;
> flag:=GetFrequency_9852;
> if flag=false then Inc(DDSRWError);
> inc(count);
> until flag or (count>9);
> str(DDSRWError,DDSRWError_S);
> Strip(DDSRWError_S);
> if count>1 then MessageLog('DDS Read/Write Error');
> if flag=false then ErrorLog('Unable to set DDS frequency');
> StoreM41T56_TW;
> end;
> end;
>
> The initialization is:
>
> PreFilterTimeConstant:=1-6/NaturalTimeConstant;
>
> Both procedures are executed once per second. Read "If NeueZeitKonstante
> then" as "If the user has set a new PLL time constant then do". If you can
> gain a certain understanding for the source then terms like
> "SetFrequency_9852;" or "flag:=GetFrequency_9852;" will indicate you that
> instead of an analogue steering of the OCXO my project used a AD9852 DDS
> circuit to steer the output frequency the digital way. For that reason it
> could steer anything from simple xtals to rubidiums and cesiums without the
> slightest interaction with the circuitry of the oscillator itself which
> made
> me call the device AOS (Arbitrary Oscillator Synchronizer).
>
> The "microcontroller" used was a BECK SC12 and you can read more about it
> here:
>
> http://www.beck-ipc.com/en/products/index.asp
>
> For a lot of people this may seem a strange choice but beware: If you want
> to handle 48 bit tuning words you should take care that your micro/compiler
> combination is able to handle 64 bit entities. Before I gained access to
> the
> IAR C compiler for the AVR range of microcontrollers the Turbo Pascal that
> I
> could run on the Beck was the only environment available for me which
> featured 64 bit "extended" floating point entities and 64 bit "cardinal"
> integer entities.
>
> The phase comparator was a simple TIC with a delay line interpolation to 56
> ps resolution in an ALTERA EPF10K10 cpld. This cpld (although specified
> with
> some ns pin to pin delay) had a very fast internal "carry chain" logic
> (neccessary for multi byte adders for example) and the carry chain elements
> could be used as a fast delay line for the time interpolator.
>
> > Understand that the key point is the PLL or the phase
> > comparator circuit.........if you want to build you own GPS-DO.....
>
> Among the key points for a good GPSDO are some things that have never been
> discussed here, for example how to detect and reject outliers in the phase
> measurements. Outliers are anything else then extraordinary and a single
> outlier may push the pll's integrator value into outer space so we MUST
> detect them before the can fire up a desaster. Unfortunately detecting
> outliers is anything else than trivial and a science of it's own called
> "robust statistics" tells us how to do. For that reason be prepared to
> learn
> more than you really want.
>
> Best regards
> Ulrich
>
> > -----Ursprungliche Nachricht-----
> > Von: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] Im Auftrag von Erno Peres
> > Gesendet: Samstag, 31. Marz 2012 15:10
> > An: time-nuts at febo.com
> > Betreff: Re: [time-nuts] CW12-TIM vs M12M and the world
> >
> >
> >
> > Hi Ulbrich,
> >
> > Sorry but not everybody a digital and/or a professional
> > guru... can you please be a more specific.... namely to show
> > us the pre filter and other circuit....if you do not mind.
> > Understand that the key point is the PLL or the phase
> > comparator circuit.........if you want to build you own GPS-DO.....
> >
> > Many thanks and best regards,
> >
> > Ernie.
> >
> >
> >
> >
> > -----Original Message-----
> > From: Ulrich Bangert <df6jb at ulrich-bangert.de>
> > To: 'Discussion of precise time and frequency measurement'
> > <time-nuts at febo.com>
> > Sent: Sat, Mar 31, 2012 2:53 pm
> > Subject: 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 anual at
> > http://www.thinksrs.com/downloads/PDFs/Manuals/PRS10m.pdf
> > and find starting on page 13 the complete instructions on how
> > to build your wn GPSDO. A basic knowledge of math,
> > programming and control theory is eeded to understand the
> > manual but then: It works. I have constructed my own DIY
> > GPSDO on the base of the information that I have found there,
> > ncluding the pre-filter. Best regards lrich
> > > -----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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