[time-nuts] Paper about DCF77 performance

[Ulrich Bangert]

Attila,

> An ADEV plot would be much more informative on the stability.

I have found an old publication from former PTB researcher Dr. Peter Hetzel.
This publication holds a diagram which (while not being exactly an ADEV
plot) holds some interesting information on the topic: It shows the STANDARD
DEVIATION of timing measurements made on DCF77's signal abt. 273 km away
from the transmitter location as a function of the averaging time of the
measurements. So no ADEV but coming close...

The diagram starts at abt. 8E-8 std dev for 1 s avaraging time and is
basically a straight line with a slope of abt. -0.8. that extends to 7E-14
for averaging times of 100 days. I list a few values:

8E-8    @   1 s
1E-9	  @	10 s
2E-10   @   100 s
5E-11   @   1000 s
2E-12   @   1 d
3E-13   @   10 d
7E-14   @   100 d

The diagram has no log sub scale so the readings are my estimate. The
diagram hold a lot of individual points between 10 and 100 days averaging
time indicating that a lot of measurements with that averaging times have
really been done.

Best regards
Ulrich Bangert
 

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Attila Kinali
> Gesendet: Donnerstag, 14. Juni 2012 07:56
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Paper about DCF77 performance
> 
> 
> Hoi Dani!
> 
> I see you've found the time-nuts as well :-)
> 
> On Wed, 13 Jun 2012 21:46:56 +0200
> Daniel Engeler <engeler at alumni.ethz.ch> wrote:
> 
> > This is my first post to this mailing list. I wrote a paper 
> about the 
> > German longwave time transmitter DCF77 which you may find 
> interesting. 
> > Here is the link, unfortunately I am not allowed to post 
> the full PDF:
> 
> There is an easy way to get around that: Prepare a second 
> paper with more data in it (all that stuff that IEEE tends to 
> get rid of during the publication process) and put that onto 
> your website.
> 
> > 
> http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6202411
> > 
> > "Performance Analysis and Receiver Architectures of DCF77 
> > Radio-Controlled Clocks", by Daniel Engeler IEEE Transactions on 
> > Ultrasonics, Ferroelectrics and Frequency Control (May 2012)
> 
> Nice paper. I haven't had time to read it yet, but a few 
> comments after i skimmed it:
> * you have a lot of simulation and measurments on BER vs SNR. 
> For time-nutty needs that's not so relevant. An ADEV plot 
> would be much more informative on the stability.
> * Also some data on the absolute timing variations vs time 
> would be nice to have.
> * Fig 23 shows a very complex board. Given that you only have 
> a relatively simple analog stage and an FPGA  i wonder what 
> the rest is for.
> * You use an LTC1562 8th order bandpass: Do you compensate 
> for it's frequency dependend delay and its variation? Or is 
> negligible compared to the antenna?
> * Do you do any temperature stabilization?
> * What kind of reference oscillator do you use?
> * You talk about 20 to 50ppm variations for XO's, are you 
> aware that these are maximum variation including production 
> variabiltiy and that the stability of an good XO is usually 
> in the range of a few ppm in office conditions (i've measured 
> an XO in a PC that showed a long term (months) stability in 
> the ppb range)
> * Why did you use an FPGA and not a simple DSP or one of the 
> more powerfull uC's like an Cortex-M3/4? The algorigthms 
> don't look computationally intensive. And that would simplify 
> the development considerably.
> * Where did you do your measurements? In Schlieren?
> * What is the application you had in mind while developing this?
> 
> 
> 				Attila Kinali
> -- 
> Why does it take years to find the answers to
> the questions one should have asked long ago?
> 
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