Complex sentence: At the suggestion of Ernest Fisk, these five stations operated under a system possibly unique to Australia, the sealed set system under which listeners-in were to buy a set which was sealed to the frequency of the station nominated.
Split into simpler sentences: At the suggestion of Ernest Fisk, these five stations operated under a system possibly unique to Australia! This was the Sealed Set system under which listeners-in were to buy a set which was sealed to the frequency of the station nominated.