Thanks to everyone for all the replies! It seems unbelievably deceptive that the calculation is so trivial. For some reason I was under the impression that the waveform shape or modulation would influence this calculation i.e. 8kHz FM has a different power spectral density to 8kHz voice, which is different to 8kHz SSTV, which is different to 8kHz "whizzbang"-mode, etc, etc. I suspect I'm missing part of the story or confusing myself with an irrelevant parameter. If someone knows what I'm referencing, I'd appreciate it if they could set me straight! On a side note, this perhaps has more to do with the wording and language of our legislation, rather than technical matters.... but would the "1W per 100kHz" apply to the entire signal? or would it only apply to the signal outside 8kHz? I think this is what Frank G0GSR is alluding to in the post above, and I'm not sure what it means either. For example, if the signal was 10kHz wide, would the restriction apply only to the 1kHz excess on either side of the 8kHz? or the entire 10kHz? Andrew VK3CHI P.S. In answer to AH7I's question, I had a quick look at legislation regarding our; CB radio, LIPD, radio-controlled model, and scientific class licences, and none appear to have a parameter like this one.