I never read this one as a kid, but I've just finished it and it's good. I wish now I had read it when I powered through all the Winston books in my school library!
A book explaining radio to children, but it's written in such a cutesy, irritating voice that I can't imagine anyone actually learning anything from it. I put it down after a dozen pages.
This one is fun: a completely improbable, but likeable, nobility called E's (for Extrapolators) are called in to make contact with a non-human, crystalline intelligence.