from 9 july 1924, however, the company began experimenting with higher power longwave transmissions from the marconi company's site near chelmsford in essex, using the call sign 5xx. the experiments proved successful and on 27 july 1925 the chelmsford longwave transmitter was relocated to a more central site at borough hill near daventry in northamptonshire. this provided a "national service" of programmes originating in london, although it remained somewhat experimental and was supplementary to the bbc's locally based services, including its main london station, 2lo.