Hi We have at least one example of the spurs being in the 40 to 80 Hz range “depending”. That strongly suggests that the original analysis is correct and that it is a spur in the OCXO rather than line noise induced issues in a test setup.
Bob > On Feb 28, 2016, at 5:49 PM, Bill Byrom <t...@radio.sent.com> wrote: > > If the spurs are at exactly 60 Hz multiples (not 120 Hz or 180 Hz) and > you are in an area with 60 Hz line power you might have magnetic field > coupling from nearby power transformers. Normal conductive shielding > won't solve this issue, and Mu-Metal or other high permeability low > frequency materials must be used. The voltage induced in ground loops by > AC magnetic field depends on the area enclosed by the loop, so twisting > wiring can help in some cases. > > I suggest a test as follows: > * If possible, move the DUT (device under test) to an area which is at > least a couple of meters from AC mains power lines and transformers > connected to AC mains power. Power the DUT from a battery based > supply. Keep any galvanic connection (any conductive wires or metal > cases touching metal benches) away from the DUT, except a single > safety ground wire. > * If that's not easy (and I don't that level of isolation is practical > for most of us), then turn off all AC mains line powered equipment > within a couple of meters of the DUT. Unplug all equipment nearby > from the AC mains power line, then plug the power supply used by the > DUT and the minimum test equipment required for the 60 Hz spur test > into a single quality AC power strip. This single AC power strip > (with only the DUT supply and critical test equipment) should be the > only item plugged into the nearby AC mains power sockets. Using a > single quality power strip will establish a safety wire ground which > is nearly a single point ground. In some buildings there can be > problems if the safety ground wires for different AC mains line > sockets have different potentials due to connected equipment or water > pipe or other external connections. > * Keep any transformers which are plugged into the AC mains line power > as far as possible from the DUT and the connections between the power > supply, DUT, and any test equipment. > * Be sure to turn off any nearby AC mains line powered lighting in the > area and see if that changes the spurs. > * Connect a heavy gauge (such as #10) copper wire between the metal > chassis or other ground point on the test equipment, power supply, > and DUT and see if the spur level changes. If it does, then you have > ground loop problems. The effective source impedance of magnetically > coupled currents is very low, so it can be difficult to eliminate > them completely. Single point ground systems are usually a good idea. > -- > Bill Byrom N5BB > > > > On Sun, Feb 28, 2016, at 12:22 PM, Adrian Godwin wrote: >> Could it be microphonic capacitors, or the crystal itself ? >> Have you got a big old heavy power supply with a buzzing transformer on >> your workbench ? >> > > _______________________________________________ > 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.
