You have a shortwave receiver then and have checked all the broadcast bands between 2.3Mhz and 26.1Mhz then.
Technically this is absolutely valid, but a little cynical and theoretical in the context. In these days, in 'the first world', for want of a better phrase, how many people are using SW receivers covering the 120-11 metre bands. I appreciate that there are radio amateurs, DXers, people who use standard time signals, monitor marine broadcasts, and so on, but this is a tiny percentage of the population.
For most people, the homeplug would seem to be a good solution. Talking about this to friends locally I've discovered that they use it between their main property and and outhouse used as a study, and it works well and has not caused any interference with various hifis, wifis, satellite and terrestrial TV, or normal FM (95-105 Mhz) and AM (MW) broadcasts.