Transmits time signal to cover end of programme (5)
I believe the answer is:
pipes
'transmits' is the definition.
(I've seen this before)
'time signal to cover end of programme' is the wordplay.
'time signal' becomes 'pips' (sounds indicating the time on the radio).
'to cover' indicates putting letters inside.
'end of' says to take the final letters.
The last letter of 'programme' is 'e'.
'pips' enclosing 'e' is 'PIPES'.
(Other definitions for pipes that I've seen before include "Tubes for fluids" , "Tubes - musical instrument" , "Hollow cylindrical shapes" , "Long tubes" , "Wind instruments" .)