On 9/22/08, Andy Green <[EMAIL PROTECTED]> wrote: > I agree it's not clear 100uF there is going to do anything good about > the problem, unless the dips are introduced directly on MICBIAS then > trying to smooth them there is the wrong place since they have already > been amplified on to there and we fight the blameless amplifier. But > actually, I didn't see we proved quite where the buzz starts from as LF > so we are not in a position to write this off as insane.
If you have problems with HF "infestation" a big cap will usually not help. The only thing you change is that reflection from an open circuit is changed to reflection from a short. ( and you will have changed the freq. of resonance which could put you even further down the drain.) Either you get rid of the crosstalk _or_ you add _lossy_ elements to your transmission line. A resistor with about the line impedance ( or 1/2 Z if you have access to the middle of the line in series with a small cap to ground can help. The same goes for ferrite beads ( or flat pieces glued onto the trace ) (the right) ferrite beads are lossy. > For both going forward and to solve issue for phones in the field, I get > the feeling we can't do justice to understanding this problem internally > and need to go talk to people experienced in this kind of RF issue. Uwe > and his folks sound like a first port of call. I know a commercial > outfit in UK I worked with before we can approach as well if needed. I plan to test a meassuring setup with my own freerunner this week. I'le contact Andy after that is running for meassuring his phone.. uwe _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
