At the time he was writing, TVs didn't know how to blank out between channels. They just broadcast the noise. Blank television screens (when the TV was on) hadn't been invented yet.
(edit: maybe that's not true, perhaps in 1984 TVs with plain blue between the channels did just about exist? I don't know, in the 80s I only had access to the sort of black-and-white TV that meant his image came across to me exactly the way he apparently intended it)