During my experiences involving audio/phone, video and data transmission, we were taught to ground the shield at one end only so we would not cause a ground loop.
I ran into problems everywhere I went with this and as much as folks disdain transformers, they are your friend in this type of problem. Don White Consultants/Interference Control Technology published a whole series on EMI, Grounding, and EMC for the military. They are located in Gainesville, VA. Brian Joseph M Gwinn wrote: > First the background: > > In some timing distribution applications, the primary source of > interference comes from different ground voltages in different parts of > the facility, such as a ship or a megawatt radar. > > The effect of differing ground potentials on a shielded cable is to pull a > large current through the shield, so there is a significant voltage > between the ends of the cable. No matter how good the shield is at RF, > one consequence is that the same power-frequency offset voltage appears on > the conductors within that shield, because the skin depth at 60 Hz vastly > exceeds the thickness of any reasonable shield. Unshielded twisted pair > will suffer the same common-mode offset voltage, perhaps more. This > offset often contains significant harmonics of the power frequency, > nominally up to the seventh harmonic, not just the fundamental. > > If the cable is shielded twisted pair, such as twinax, the offset appears > as a common-mode voltage on the two conductors, and (if not too large) is > eliminated by the CMRR of the receiver. > > If the cable is coax, the offset voltage appears added to the timing > signal voltage, and if the offset isn't too large the signal receiver will > be sufficiently immune to this conducted EMI. > > > And now the question: > > What standards exist governing required immunity of signal ports to these > ground-loop induced power-frequency (hum) voltages? > > All the conducted suseptability standards I've found cover only > frequencies exceeding 10 KHz, not power frequencies and their harmonics. > > > Thanks, > > Joe > > > _______________________________________________ > 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.