I read in sci.electronics.design that John wrote (in ) about 'Powerline modem', on Thu, 10 Feb
2005:
This can be done very well using frequencies below 150 kHz which don't create huge EMI problems.
Not at any price; the emission levels 3 to 30 MHz are 60 dB or so above those currently accepted. It's very far indeed from a marginal increase.