On 7/17/2010 11:10 AM, Douglas Furton wrote: (JLR edited) > ...Perhaps switching PSs are better engineered now than in the past... =====
I can tell the assembled multitude that this assessment is correct. Before retirement, I did a lot of weak-signal work in the lab (related to NMR imaging), and in the earliest days of this work, ca. 1970 or so, I used Apple-2-Plus machines for data collection. Some of you may recall that these small microcomputers were powered by open-board switching power supplies, and the cabinets contained no shielding whatsoever. They were exceedingly potent sources of RFI and had to be kept "isolated" from the spectrometer circuitry. At some point, I considered "isolating" them by taking them out in a field and burying them. Fortunately, technology advances. My comments about proximity were to the point that modern devices (computers or switching power supplies) are very well shielded, as are modern XCVRs. The Radio Shack 25 amp switchers that I have contain good shielding AND massive ferrites on the inside of the cabinet directly on the DC terminals. The AC line cord is similarly ferrite-trapped, directly inside the metal cabinet. The computers (a la FCC type-acceptance regulations) have RF-tight enclosures with close-fitting fingerstock around the openable places and below-cutoff screening on the fan ports. My K2 and K3 are exceedingly well shielded...surely an open 100-watt source a couple of feet from a computer would make itself known. I think it is really a question of "physician, heal thyself" -- I believe that some truly have the problems they report, and that they have taken the correct steps to ameliorate them. But...my overall opinion is that switching power supplies have taken a bad rap. My linear supplies are gathering dust, keeping their shelving from floating up into the air. Maybe the way to convince oneself one way or the other is to buy an inexpensive Astron or Radio Shack supply and try it. Also...with care...batteries make very good "filters." John Ragle -- W1ZI ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
