For LW, MW, and lower HF, a homebrew Windom antenna with a 4:1 W2DU current Balun. But for FM, I mostly use the telescopic built-in whip antenna. One EXT modification that I did with EXT Antennas for that radio was to make a plug with opposing 1N4148 diodes across the center and GND conductors, for decent spike protection. Where I'd gotten that idea from were the Sony ICF-2010 portable gurus that did that to protect that radio's static sensitive J-FET front-end. BTW, that is interesting that your ATS-803A doesn't seem to like +9VDC going to it. I'm not using the original wallwart for my radio, but one from a trashed cordless phone base unit that is a transformered wallwart that happened to be +9VDC, 500mA, loaded. So, that worked out fine. BTW also, you might be able to find such one yourself at any junk store, or the Salvation Army, or Good Will, stores. I'm buying up every transformered wallwart I see, most for around $1.00 each. You just never know what they might be useful for. Better than +$20.00 for a new one.