Hello, while waiting fot the final doom, or a new job (tough times here) here is another update of the work I'm doing, sorry for the looong mail, hope I'm not boring the readers.
I have a question about a some measurements I made, and I'd like an opinion about a frontend schematic I designed. First the question about the problem: in this graph (bottom right) there is the time interval between the PPS from the PA6H GPS module and the 10MHz form the FE5680A, uncrambled and corrected for linear drift. The graph periodically makes big steps, and this happens in the morning hours, in the few captures I made so far the fact happens around 6am-8am in the morning: http://www.flickr.com/photos/14336723@N08/8294131424/ another previous capture with span enough to include 2 mornings: http://www.flickr.com/photos/14336723@N08/8294131660/ I will make more tests to check if the problem is in the gps receiver or in the FE5680 or in the way I'm taking measurements. This will take a while. Maybe there is a simple explanation that I cannot see since I'm a total newbie i this field. Where should I search first for the problem? How I'm taking the measurements: the measurements are taken with the racal 1992 connected to the point OutD in the centre of the frontend I'm building: http://www.flickr.com/photos/14336723@N08/8293076065/ The OutD will spit out a short negative pulse, the width of this pulse is the same (or very near) than the phase time interval between the rising edges of the pps and the 10MHz. The counter logs the pulse width using a 100MHz scope probe set to 10x, DC coupled. The plots are made using this script I wrote for the task : http://pastebin.com/XmKQp9gR The (rude) script tries to unscramble the data, remove outliers and correct for linear drift. If it's useful I will upload the raw log data. The frontend circuit: As I wrote before I'm trying to feed a microcontroller with 10MHz from a Rb oscillator and a PPS pulse from a GPS module and see if I can obtain a good starting point for building my own GPSDO. Now I'm testing a front end that will present to the micro both the PPS and 10MHz nicely squared, and an analogue representation of the time interval between the rising pulses of the sources. What do you think of the circuit I designed? (thanks to many resources coming from this list, I passed much time on ko4bb site and many others I dont even remember, thank you all!) here the asc file for LTSpice: http://pastebin.com/94H78jxs I'm using components I had around or scavenged in scrap electronics I had. The TAC seem to work, but now I need a better opamp (the LM358 has too much current flowing in-out of the inputs), here a pair of captures taken directly from C1 capacitor, 90nS pulse: http://www.flickr.com/photos/14336723@N08/8293075961/ and a 50nS one: http://www.flickr.com/photos/14336723@N08/8294131200/ The red trace is the input GPS PPS. Fabio Eboli. _______________________________________________ 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.