Hi The amplifier board was sitting in mid air with no shielding. Stray pickup from who knows where *is* a possibility.
Bob > On Mar 25, 2020, at 6:32 PM, John Miles <[email protected]> wrote: > >> -----Original Message----- >> From: time-nuts [mailto:[email protected]] On Behalf Of >> [email protected] >> Sent: Wednesday, March 25, 2020 9:46 AM >> To: 'Discussion of precise time and frequency measurement' >> Subject: Re: [time-nuts] Noise Floor >> >> Phase noise looks pretty good. ADEV has some weird "stuff" going on. Time >> to start tearing the board apart to see what's wrong with it? >> Maybe there's some noise in those resistors .... let's go !!!! >> > > Resistor noise won't normally show up on plots at this level, but it does > look like there is some kind of periodic disturbance near 1 Hz. Could be a > thermal artifact due to convection currents on the board, or possibly a case > where large undamped LC components have been used in a power supply filter or > bias network. > > I'd be more likely to suspect crosstalk from a nearby 5 MHz source that isn't > quite on the same frequency, which should be easy enough to rule out. Poor > cable shield integrity can also encourage this type of artifact to appear, > even in the absence of an obvious interferer. > > On the phase noise plot, the 53100A thinks it's an instrument spur and is > removing it. It's very unlikely to be one, but this process will never be > 100% reliable, especially in short-duration measurements. You can see a > suspiciously-flat segment centered at about 0.9 Hz, which often indicates > that a spur is being suppressed automatically. The stability data doesn't > undergo any automatic spur detection or removal, so when you see ripple in > the ADEV plot that doesn't correspond to an obvious spur on the PN plot, it's > a good idea to either let the measurement run longer or set the 'Spur min > offset' value to 10 Hz or so. > > -- john > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
