[time-nuts] Paper about DCF77 performance

Attila Kinali attila at kinali.ch
Thu Jun 14 05:56:19 UTC 2012


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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