I've seen switchers cause noise envelopes and picket fences well into the MHz range. The switching freq is what (?) 100 kHz, 150 kHz ...
But, for some reason a pulse with a 20 nano-second period makes me think that maybe a digital signal such as a square wave is getting differentiated by the parasitics of the construction. In that case, I personally would start looking around for a clock roughly ~25 MHz in freq or a signal (refresh/strobe?) that may resident on a trace like a bus in the backplane. Just a guess... Regards, Doug ---------- > From: Bob Tims <rt...@emx.ericsson.se> > To: emc-p...@majordomo.ieee.org > Subject: Noise in Power Lead > Date: Tuesday, January 06, 1998 10:21 AM > > > Happy New Year All, > > I have an interesting noise problem brought to me. > The noise is a 500-900 mV pulse seen at 50 MHz on a > power lead from a DC to DC converter (48V to 5V) to a > VME cage. > There were two scenarios: first, both the power supply > and the cage are earth-grounded, and the pulse is seen > at both the power supply and the cage. Second, the cage > is left floating, and the pulse is only seen at the > power supply. > The noise seems to be a ring, and the leads between the > supply and cage are fairly long. > Has anybody seen something like this before, or does anybody > have any suggestions or comments? > We have several ideas, but not much time. > The frequency and the fact that the pulse reaches almost a volt > concerns us greatly. > Thanks in advance, > > Bob Tims > Standards and Compliance > rt...@emx.ericsson.se > > The opinions expressed in this correspondence in no way reflect > the opinions of Ericsson Inc. > > > RCIC - http://www.rcic.com > Regulatory Compliance Information Center > >
