As far as I know, the word radio in Spanish belongs to the substantivos ambiguos, i.e. the word exists in both genders with different meaning. (la radio = the radio, el radio = the circumference, the chemical element radium, the radius bone)
So, how does all of this transfer into Catalan?
It doesn't have the same meaning in masculin or in femenin.
In femenin (la radio) it's the electronic equipment, in masculin (el radio) is a segment (radius in english) or a part of a bike (spoke in english).
In catalan we have the same: "la ràdio" (in femenin for the radiorreceptor) and "el radi" (in masculin for radius or spoke).