The most common and most likely answer to this crossword clue is the 4 plus 3 letter word SIGN OFF
I've seen this crossword clue in The Daily Telegraph
S
I
G
N
O
F
F
More clues leading to the result SIGN OFF
Buddy explains!

The straight part
We know that "makes one stop broadcasting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case makes one stop broadcasting = sign off.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 SIGN OFF mean?
SIGN OFF noun- The act or process of signing off (approving with a signature).
- The process of exiting a computer system; logoff.
- A bid indicating that one's partner should pass.