Complex sentence: The previously experimental long-wave station 5XX moves from Chelmsford to Daventry and becomes, as the first station to achieve near national coverage, the main transmitter of the BBC National Programme.
Split into simpler sentences: The previously experimental long-wave station 5XX moves from Chelmsford to Daventry and becomes the first station to achieve near national coverage. The Daventry station will later become the main transmitter of the BBC National Programme.