Hi Olin, Well, the first thing I did was to design the switcher layout to try to minimize radiated emissions. I also had a copper shield can over the switcher components, which was connected to ground. However, I am still learning when it comes to good board layout for switchers so I suspect that I could have done a better job. I agree with you, though, that shielding is a secondary measure - one should always start by minimizing the radiation to begin with. My receiver is a general coverage shortwave type covering 0.1 to 32MHz. The switcher was a National "simple switcher" series, I don't remember the exact part number. I think it ran at 80kHz if I remember correctly. Basically I could hear a small band of noise every 80kHz as I tuned, well up into the HF spectrum. I think that the National part probably placed such a high emphasis on efficiency that it turned on its output stage very hard and fast, given that it produced audible harmonics well above 10MHz. The effect on the receiver was not overwhelming but definitely annoying. Sean On Mon, Nov 3, 2008 at 7:52 AM, Olin Lathrop wrote: > Sean Breheny wrote: >> As a hobby project I have slowly been building a high-performance HF >> receiver over the last few years. I originally used a switching power >> supply in it. Granted, I'm only slightly beyond newbie when it comes >> to switching power supplies, but I have to say that I found it >> impossible to keep the harmonics from the switcher from making it into >> the receiver. I tried shielding and massive filtering on the input and >> output leads to no real avail. I did not try magnetic shielding, >> however the physical separation between the switcher and the rest of >> the receiver was such that I would find it hard to believe that there >> could be direct magnetic coupling. > > It sounds like you tried everything except the one thing that should be at > the top of the list, which is proper grounding and attention to where the > high frequency loop currents go. This is the most important single thing > for keeping any sort of switching noise from going elsewhere. > > A few years ago I redesigned a receiver that had to decode the information > from two 434MHz receiver and pass the resulting data along over ethernet. > The original design used a 6 layer board with the digital section in a can. > The bottom layer formed one face of the can, and a separate piece of custom > fabricated metal was soldered over the digital and switching power supply > section. Needless to say, this was a expensive solution. > > My redesigned version replaced the analog data slicers with a dsPIC, used > two switching power supplies instead of one, and only a 4 layer open board > with no sheild. However, I paid careful attention to where all the high > frequency loop currents were from the digital parts and the switching power > supplies, used one layer for a pervasive ground plane, and used sub ground > planes for noisy sub-sections. In the end we beat the FCC emissions limit > by almost 15dB, and got a much lower noise floor from the two RF receivers. > The net result was that it could pick up transmissions from over twice as > far and cost 30% less to produce. > > > ******************************************************************** > Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products > (978) 742-9014. Gold level PIC consultants since 2000. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist