Monumental...
On Sat, Mar 22, 2014 at 12:25 AM, djl <d...@montana.com> wrote: > Well done! > Don > > > On 03/21/2014 03:55 PM, Tom Van Baak wrote: >> >> Designing a GPSDO is a permanent topic of time-nuts, and always invites >> lots of opinions and methods. >> >> The net performance of a microcontroller-based GPSDO is mostly due to the >> following ingredients: >> - the stability of the OCXO (or TCXO or Rb or whatever the LO is) >> - the stability of the GPS 1PPS (including sawtooth correction, or not) >> - the disciplining algorithm itself, and user-settable configuration >> parameters or filtering >> - the finite resolution of the TIC or phase comparator >> - the finite resolution of the DAC/EFC >> >> Normally what happens is that someone spends weeks or months or even years >> working on each of these ingredients, measuring, comparing, tweaking, or >> maybe just hoping for the best. These measurements can take a lot of time, >> or be difficult to replicate. >> >> I have an alternative. >> >> It's a simple software tool which takes *real* GPS phase data, and *real* >> LO phase data, and a *real* GPSDO algorithm(s) -- along with optional >> resolution of the TIC and optional resolution of the DAC -- and then creates >> GPSDO phase data through *simulation*. You can then plot this virtual GPSDO >> phase data with Stable32 or Plotter or TimeLab or your favorite phase / >> frequency / stability tool. >> >> So instead of waiting hours and days to test your new filtering idea, or >> your new GPSDO algorithm, or to compare the effect of a 10 ns vs. 1 ns vs. >> 100 ps vs. 10 ps TIC, or to compare the effect a 10-bit vs. 16-bit vs. >> 24-bit DAC -- you just run the simulation on your PC and get an answer in a >> few seconds. >> >> Have a look and let me know what you think. The tool is gpsim1.c (Windows: >> gpsim1.exe) under: >> http://www.leapsecond.com/tools/ >> >> For this to work, one needs actual GPS data and actual LO data. I have a >> growing collection of sample data files here: >> http://www.leapsecond.com/pages/gpsdo-sim/ >> >> For example, if you run this command: >> gpsim1 gps-mtk3339.txt ocxo.dat >gpsdo.txt >> >> and use TimeLab to plot these three files, you will get the attached plot. >> No solder, no instruments, no antenna, no waiting, no guessing. A complete >> 4-day simulation takes just 3 seconds (on my 10-year old laptop). Load the >> simulated phase data with 'L' in TimeLab and view phase, frequency, ADEV, >> MDEV, TDEV. Answer your GPSDO design questions in minutes instead of weeks. >> >> Try different parameters. Try different GPS boards. Try different >> oscillators. See if you can make the best ADEV. Try new disciplining >> algorithms. Make the PID more complex. Change the filtering. >> >> /tvb >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.