"The probability for 'intelligence? Or better yet that for technical civs that can build radios?"

Or those that could but decide not to.

Does an advanced civilization necessarily need to be highly technological? Maybe the ones that have a drive to that end don't last long enough to be detectable by us at this time. I can imagine an intelligent society without high tech.

Wouldn't most of human history other than last hundred years count?
Thereby requiring less imagination?

Or if our world was smaller and there wasn't a New World, we could still be in that intelligent society without high tech- and France would probably still be ruled by a monarchy. And that kind of thing could continue for thousands of years- as it did in China and India.

And instead of going to the Moon, perhaps the current project could be some great wooden sailing fleet going somewhere for some noble reason.
And high technology of the day might involve preventing wooden ships from rotting.