I tried stringing up 3 meters of random wire (connected to a 15 meter roll of wire, so 12m of wire was coiled up at the end of the 3m) as an antenna, extended on the floor of my 2nd floor residence and stuck directly into the antenna connector of my FT-817. It was unusably noisy and even booming SWBC stations audible on my loop were drowned in noise.
Next experiment was to raise the wire off the floor. I made a very rough "loop" (more like a tangled mass) about 1m in diameter and hung it from a curtain rail, leaving about 3m of wire at each end of the loop. The 3m wires at the ends of the loop draped down from the curtain rail to connect to my radio's antenna and ground terminals. Result was much less noise. I could make out many SWBC broadcasters and some digital signals on 10m. Not as quiet as my loop, but possibly acceptable for SWBC.
Conclusion: there must be noisy wiring in the floor, and, presumably, the ceiling as well (which is the floor of the upper story).
A balcony-mounted wire antenna should do better still (mainly for receiving). But what would be the proper way to feed a random wire antenna? If I just run the wire from the balcony to inside, it will lie on the floor and pick up noise. Would it make sense to connect, on the balcony, the random wire to the center conductor of a piece of coax, then run the coax inside (along the noisy floor) and connect it to the rig? Would that reduce noise pickup from the floor since the coax is shielded? Would the rig need to be grounded?
Please bear with me as I learn the fundamentals of signal transmission and propagation...
EDIT: Related link indicates grounded coax might help: http://www.radiobanter.com/archive/inde ... 39945.html