Hi, Phil!

I read that, too - in a pre-1980 NASA publication on SETI (paperback, collected papers from a symposium). I don't have it with to check citation information, but that might be enough of a start for interest parties to track it down. I also recall the article saying that, in that region of the EM spectrum, Earth is a far brighter source than Sol.

Observed at a distance, our orbital motion (detectable as Doppler shift) might make it easier to deduce that the source of the radiation was artificial... The ETs might even recognize the emission as radar - that is, its purpose - if they had also gone through a similar stage in their political/military/industrial history.

E'