[time-nuts] Paper about DCF77 performance

[Daniel Engeler]

Hi Attila

Thanks for the feedback.

> * 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.

Yes that would be nice, but my spare time is short for this and the
dozens of other ideas I 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.

Just the usual power supply, DAC for debugging FPGA-internal signals,
galvanically isolated USB for logging, debug headers.

> * 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?

I do compensate for it. The remaining uncertainty is taken into
account in the paper.

> * Do you do any temperature stabilization?

No, but it would be a nice addition.

> * What kind of reference oscillator do you use?

Abracon ASV-12.000MHZ-E-J-T, 20 ppm, 12 MHz

> * 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)

I worked with worst-case ranges as if it were a mass production.

> * 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.

At that time, I wanted to have some fun with FPGAs. It would also work
on a uC, which BTW already is my next project. Both ways have
advantages, for example the clock correction algorithm is easier to
implement on an FPGA, while the signal processing would be simpler on
a uC.

> * Where did you do your measurements? In Schlieren?

Yes.

> * What is the application you had in mind while developing this?

Building the best DCF77 receiver in the world :-)

Regards,
Daniel