The most common and most likely answer to this crossword clue is the 6 letter word TRANNY
T
R
A
N
N
Y
Buddy explains!

The straight part
We know that "radio" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case radio = tranny.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TRANNY mean?
TRANNY noun- A transsexual, transgender or transvestite person, usually a trans woman.
- A transistor radio.
- A mechanical transmission, a gearbox.
- A transformer.
- A transition between moves.