This is slightly off topic - but since there is such a generous group of guys that are very knowledgable in electronics (and since my brain is a little soft in this area), I think I'll toss this request out and hope for the best.
First off - please reply off the list since this does not pertain directly to Elecraft equipment (except that it might be fun to eventually take the same design and build a larger p/s for the K2/QRP). My goal is to build a non-switching, voltage regulated 9V/1.5A power supply with enough isolation and filtering to keep RFI out of a Grundig Satellite 800. My father has one of these radios, and so do I (unfortunately, he lives out of state - so I couldn't compare the two radios and p/s side by side). When I visited him over the holidays, I discovered that the OEM power supply my father has is either producing RFI or is conducting RFI, because he can tune in daytime AM/MW signals from over 100 miles away when running the thing on batteries, but he has a hard time with signals beyond 50 miles away as soon as he plugs the power supply into the outlet (this was AFTER we already turned off the worst RFI generating offenders in the house). The Grundig Sat 800 power requirements are spec'd at 7-10V DC up to 1 Amp (530mA with 1/4W output and lamp off, and 830mA with 1/4W output and lamp on), and it says in the manual that the supplied adapter is 9V/1.5A. I've got an old 1987 copy of the handbook which I've got up in the attic for reference, and I realize some of the basic things (from my license/testing days) that go into a power supply (transformer, diodes, capacitors, inductors, regulators). I want to actually build my own power supply from scratch - starting with the transformer. If I'm not mistaken, I should be able to use a medium-large toroid core and some heavy wire to do this. [I could go down to Radio Shack and buy a wall wart, but I want to actually make something that is going to work 'really well' in terms of reducing RFI passing through the AC power supply - something that a cheap power adapter probably won't be designed for.] So - here's where I'm hoping you can help me with... What core (size and material composition) should I use for transforming an AC signal? How many windings of what kind of wire would be the 'best' for the power requirements of this supply? Should I build a 120/12V transformer and voltage regulate it down to 9V, or would it be better to simply build a 120/9V transformer and rectify the AC and smooth it out with passive components? How can I best filter out RFI being carried on the AC line? Are there any other considerations I should be aware of? Do you know of any helpful websites I should visit (I haven't googled this topic yet)? I'm sorry to waste the bandwidth of others here. Any help supplied is greatly appreciated! - Daniel AA0NI Oklahoma City _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
