Maybe I can help... Zik Saleeba wrote: > Apologies about the incorrect topic - reposting in [EE]... > > On 9/4/06, Zik Saleeba wrote: > >> I'm making a control system for an autonomous plane. Every gram counts >> so I'm planning on using a high frequency step-down switching >> regulator to provide power. My worry is that EMI from the LT1940 >> switcher may interfere with radio communications. If you design the switcher according to the recommendations of the chip maker, you will not radiate heavily enough to cause interference. Most important- Use a multilayer PCB of which at least one layer is GND. Next, use a shielded inductor, and make sure the inactive (VCC) end of the inductor is the shield end: most assembly houses are not aware that inductors are sometimes "polarized". I have noticed that the National Semi 50Khz "Simple Switchers" seem to generate less EMI than the higher frequency ones. Just a place to start. >> The plane has two >> independent radio systems - one for two-way telemetry and one to allow >> override of its control system when bugs happen. So I don't want EMI >> from the switcher to screw up either of these systems. >> What isn't clear to me is how I can tell how much of a problem I have >> with EMI. What can I do to measure the amount of EMI or the effect >> it's having on the radios? Preferably without crashing the plane in >> the process, that is. >> There are people all over the www that sell "broadband sniffers"; these are normally used to pick up room "bugs", but they also work well as general EMI locators. I paid less than $100 for mine. >> And if there are problems with EMI what would the lowest weight >> solutions be? Would putting foil around the power supply and some >> small ferrites on the power lines be likely to do the job? >> Be careful with ferrites, sometimes they ADD EMI if not carefully used. Usually, the ferrite needs to be used with caps on both ends to GND. Copper foils DO help, if you need it. But I don't think you will. Just layout the switcher in as tiny a footprint as possible; the smaller you make it, the quieter it will be. --Bob >> Thanks, >> Zik >> >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist