Old tracks supposedly set for broadcast by large Spanish lady (3,5)
I believe the answer is:
ley lines
'old tracks supposedly' is the definition.
(supposed paths once connecting ancient sites)
'set for broadcast by large spanish lady' is the wordplay.
'set' becomes 'lay' (synonyms).
'for broadcast' indicates a 'sounds like' (homophone) clue.
'by' is a charade indicator (letters next to each other).
'large' becomes 'l'.
'spanish lady' becomes 'ines' (Ines is a common Spanish name).
'lay' sounds like 'ley'.
'ley'+'l'+'ines'='LEY LINES'
(Another definition for ley lines that I've seen is " straight paths".)