[Andrew2]

From everything I've read in the past, Radio 390 had only 10kW, but its efficient tall mast enabled it to claim 35 kW to attract advertising. I don't know if it's true, but I see it quoted often.
R 390 was a useable signal up here in Manchester, even in the daytime. We could also hear Radio City, Radio London (not so good) and of course Caroline North. Caroline south was only just audible. Radio 270 off the NE coast was decent and Radio Scotland was always a good signal at breakfast time while getting ready for school.
It's worth mentioning that noise levels on MW were generally much lower than they are today. I suspect the pirates' signals would mostly be buried under modern-day hash.