Oddly enough I do have a PPS output from the TCXO I was measuring. It's on a little board I made and there is a PicDiv right on it. I'll have to play around with that.
I did notice the aliasing issue trying to measure a 12MHz crystal. It appeared to have incredible stability and accuracy for a plain old XO... Also it has a frequency offset of over 1kHz, and I noticed that I had to manually type in the correct initial frequency during setup to have meaningful data in the frequency difference view. i.e, 12001053 instead of 12E6. But of course with a marginally stably oscillator, that poses a problem. How long do I wait to find a mean frequency to type in...? It makes total sense why this is so in TI mode, but still it's one more thing to deal with. I think I'll stick with frequency mode for most things. Many of the oscillators I want to measure are right around 10^-8 or 10^-9, and I'd hate to constantly be fighting the noise floor of the instrument. I'll treat the data from frequency mode as relative and that should get me what I need. At least until I own a better instrument. Thanks Dan On Tue, Jun 30, 2015 at 10:49 PM, John Miles <[email protected]> wrote: > Yep, it will ignore any non-numeric data like "us" suffixes. It will > always interpret incoming data as seconds, so the 1E-6 scale factor is > appropriate if the counter is returning microseconds. I'll tweak the > mouseover help text for the scale factor field to clarify that. > > I think you're basically getting valid data. The 53131A's one-shot > resolution is 0.5 ns, and you're seeing about 2E-9 residual ADEV at t=1s. > It's in the right ballpark, anyway... e.g., on a 20-ps HP 5370, the > residual ADEV at t=1s will usually be in the neighborhood of 30-60 ps. > > I would, however, be worried about aliasing with a TCXO. If its frequency > is more than 5E-8 off -- meaning it drifts more than 50 nanoseconds per > second with 10 MHz at the STOP jack -- its error will end up > underrepresented in the measurement. In this case your oscillator is > drifting quite a bit (as expected) -- look at the 'w' view of the original > phase compared to the unwrapped 'p' phase. You could try putting 1pps on > both the START and STOP jacks but that'll require more futzing with scale > factors, 1pps dividers and the like, and may leave you more vulnerable to > trigger uncertainty from various causes. For measurement of a TCXO, I'd > stick with frequency mode. The ADEV plots won't be 100% kosher but they'll > be fine for relative comparisons with other plots from the same measurement > setup. > > -- john, KE5FX > Miles Design LLC > > > > -----Original Message----- > > From: time-nuts [mailto:[email protected]] On Behalf Of Dan > > Watson > > Sent: Tuesday, June 30, 2015 5:05 PM > > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] Help with my ADEV measurement setup > > > > I tried both the PPS and the 10MHz signal on channel 1, with the 10MHz > DUT > > on channel 2. Tom emailed me and it turns out the software was not > > detecting the units correctly from the serial string. (What are 6 powers > of > > ten between friends, right? :) ) Likely a settings mistake on my part, I > > sent him a screen cap to see what's up. > > > > None the less, I manually enter the time units and was able to plot some > > data. I attached a new screen cap. How does this look? > > > > Thanks > > > > Dan > > > > On Tue, Jun 30, 2015 at 5:36 PM, Bob Camp <[email protected]> wrote: > > > > > Hi > > > > > > Are you using a PPS as the “start” and the 10 MHz as the “stop” or > > > comparing two PPS signals? > > > > > > Bob > > > > > > > On Jun 30, 2015, at 2:47 PM, Dan Watson <[email protected]> > > wrote: > > > > > > > > Hi, > > > > > > > > I'm trying to take some ADEV measurements with my 53131A, and I'm > > having > > > > some issues. This is my setup: > > > > > > > > - 53131A with the OCXO option. Calibrated against a T-bolt. I also > did > > > the > > > > TI Quik cal and it passed > > > > - I'm using RS-232 out with a null modem cable into a Serial-USB > > > converter > > > > - Software is TimeLab in talk-only mode. 53131A check box is checked. > > > > - The counter is in TI mode, with a T-bolt on Channel 1 and DUT on > > > Channel 2 > > > > - A delay of 1 second is set on the counter. TimeLab seems to > accurately > > > > detect this interval > > > > > > > > I started measuring various devices, and could never seem to get > better > > > > than around 1x10^-6. Even my Rb was showing a 1 second ADEV of 10^-6. > > > > Finally I put the T-bolt on channel 1 with common mode on to both > > > channels, > > > > and it still measures around 10^-6. A picture of that is attached. > Surely > > > > this can't be right. > > > > > > > > I tried frequency mode and it gives ADEVs of 10^-12 on the Rb and > T-bolt, > > > > as expected. I understand the issues with filtering that the 53131A > does > > > > internally on this mode, but at least it shows my setup is working to > > > some > > > > degree. It's TI mode that seems to be wonky. > > > > > > > > I'm probably doing something really stupid. > > > > > > > > Thanks for any help you all can suggest. > > > > > > > > Regards, > > > > > > > > Dan W > > > > <adevtest.png>_______________________________________________ > > > > time-nuts mailing list -- [email protected] > > > > To unsubscribe, go to > > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > and follow the instructions there. > > > > > > _______________________________________________ > > > time-nuts mailing list -- [email protected] > > > To unsubscribe, go to > > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
