Since you mentioned interference on longwave, at least you get something on your R75 at those frequencies. On mine, I don't get anything from MW; instead I run into one loud AC hum after another as I tune up and down the band. Because of that, even though we have five NDBs within reception range, I can only hear the closest one, which is just 2 miles away.
The ATS-909X, on the other hand, gets all of those NDBs just fine without all the power line hash, even when running on the AC adapter, but then it has a built-in loop antenna, whereas I only have a 23-ft. length of wire for the R75. The loop is very directional, too, so that helps quite a bit.
The odd thing about the portable, however, is that once in a while I hear a siren-like sound on various LW frequencies, sometimes covering up the weaker NDBs. It sounds like one of those infernal car alarms. I couldn't find the source, until I happened to notice that those sirens start rising and falling in pitch exactly in time with the flashing LED on my laptop that indicates sleep mode. As soon as I wake the computer up, the sirens stop. This is certainly not a radio-friendly computer, because unless I put it to sleep it puts strong carriers in various places on HF, even if it's running on battery power.
