That's correct: "Five by five" = "Loud and clear."

It's old radio terminology for rating an incoming radio signal. 5 (out of 5) signal strength, aka "Loud," and 5 (out of 5) signal clarity, aka "Clear."

In actual radio comms a given signal could be say, 5:1, super strong but so distorted it's utterly unreadable, or 3:3, reasonably strong and clear enough to pretty much understand it, or any other combination. Even 1:5 is possible, being a signal as soft as a whisper from across the world, but in such calm propagation conditions that it's clear as a bell.

Source: I love me some shortwave radio!