On 9/5/2011 11:30 AM, Mark Bayern wrote: >>> "whose output transformer is very small with few windings ... > > But that is not a transformer-less SMPS. It does have a transformer.
No magic here. Aircraft AC power used to be 400 Hz, and may still be. It was[is] pretty simple. At 400 Hz, you need a lot less iron in alternators, motors, and transformers so they weigh a lot less. The concept has been around a long time. The turbine generators we used on airborne missions in the mid-60's were 400 Hz, both for weight and because turbines run at high RPM. Two troops could easily carry a 10 KVA turbine generator at a jog. Its diesel 50-60 Hz equivalent was mounted on a trailer and weighed about 1,500 lbs. The 400 Hz power supplies for the KWM-2A's, replacing the 516-F's, weighed about 3-4 lbs, including case. Nothing magic about 400 Hz either, that's just what was "engineering-ly convenient" in airplanes since it was generated by rotating machinery. Use an electronic switch at 25 KHz to create a square wave and you can use a transformer wound on a ferrite core ... even lighter ... but still a transformer. Good for us that power distribution stayed around 25-60 Hz. 25 KHz would have radiated all over the place, and does from an SMPS -- right into your receiver. SAQ in Grimeton, Sweden was on 17.2 KHz and did pretty well on the transatlantic circuit. :-) If I ever make it to Scandinavia, that alternator is on my "must see" list. 73, Fred K6DGW - Northern California Contest Club - CU in the 2011 Cal QSO Party 1-2 Oct 2011 - www.cqp.org ______________________________________________________________ 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
