Hi Yet another reason to nuke the battery and the A2 board.
It is amazing just how small a signal can mess things up at the levels involved in a good frequency standard. The old “when in doubt, throw it out” mantra may be a good one to keep in mind relative to a lot of add on features…. how much does a PIC-DIV pull compared to the 1 pps section of one of these old beasts (Cs or Rb)? Lots to think about. Bob > On Feb 26, 2018, at 2:20 PM, Tom Van Baak <t...@leapsecond.com> wrote: > >> at telling you it was sitting on top of a power transformer. It didn’t >> matter a lot > > I did ten runs of various standards that were within a couple of meters of > the bench; the TimePod did not move the entire time. Each standard had a > different looking PN plot, so I'm pretty sure the 120 Hz spur we see is the > 5065A itself, not something in the lab. > > File http://leapsecond.com/tmp/2018b-Ralph-2-pn.png is attached. > > Fun fact -- there's a wide spur at ~2 Hz on the 5065A phase noise plot. What > do you think that is? On a hunch I opened the front panel and reset the > blinking amber battery alarm lamp, and voila, that noise went away. Makes > sense when you think of the power variations associated with a blinking > incandescent lamp. > > /tvb > > ----- Original Message ----- > From: "Bob kb8tq" <kb...@n1k.org> > To: "Tom Van Baak" <t...@leapsecond.com>; "Discussion of precise time and > frequency measurement" <time-nuts@febo.com> > Sent: Monday, February 26, 2018 7:00 AM > Subject: Re: [time-nuts] Allan variance by sine-wave fitting > > > Hi > > One of the TimePods that I had access to in the past was particularly good > at telling you it was sitting on top of a power transformer. It didn’t matter > a lot > which instrument the power transformer was in. For some weird reason it > was a good magnetometer at line frequencies. I never bothered to send it > back for analysis. Simply moving it onto the bench top (rather than stacked > on top of this or that) would take care of the issue. > > As far as I could tell, it was just the one unit that had the issue. None of > the > others in the fleet of TimePods seemed to behave this way. Given that they > normally are very good at rejecting all sorts of crud and ground loops, it > was > somewhat odd to see. > > Bob > >> On Feb 26, 2018, at 7:13 AM, Tom Van Baak <t...@leapsecond.com> wrote: >> >>> BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot? >> >> The ADEV wiggles aren't visible with normal tau 1 s measurements. But since >> the TimePod can go down to tau 1 ms, when I first measure a standard I like >> to run at that resolution so effects like this show up. Once that's done, 1 >> ms resolution is overkill. >> >> In this case it appears to be power supply noise. Attached are the ADEV, PN, >> and TDEV plots. >> >> The spur at 120 Hz is massive; there's also a bit at 240 Hz; almost nothing >> at 60 Hz. When integrated these cause the bumps you see in the ADEV plot. >> It's best seen as a bump at ~4 ms in the TDEV plot. >> >> Note the cute little spur at 137 Hz. Not sure what causes the one at ~3630 >> Hz. >> >> /tvb >> <5065a-adev.png><5065a-pn.png><5065a-tdev.png> > > <2018b-Ralph-2-pn.png>_______________________________________________ > 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.