Objectives of radio mast from time to time (4)
I believe the answer is:
aims
'objectives' is the definition.
('aim' can be a synonym of 'objective')
'radio mast from time to time' is the wordplay.
'from time to time' indicates alternate letters (letters removed on a regular basis).
'radio'+'mast'='radiomast'
The alternate letters of 'radiomast' are 'AIMS'.
'of' is the link.
(Other definitions for aims that I've seen before include "Purposes or intentions" , "Sets sight on, having ambitions" , "Targets and ambitions" , "Objectives; points" , "Objectives, purposes" .)