When the BBC first began transmissions on 14 November 1922, the technology for both national coverage and joint programming between transmitters did not exist – transmitter powers were generally in the region of 1 kilowatt (kW).
Marconi began experimenting with higher power transmissions from a site in Chelmsford under the call sign "2MT" in July 1924. The experiments were successful, leading to the development of both shortwave international broadcasting and longwave national broadcasting, the latter with the call sign 5XX.
In 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 local services. Initially the national programme was transmitted on 187.5 kHz longwave but this was later changed, with the opening in 1934 of a new high-power longwave transmitter site at Droitwich, to 200 kHz, which was to remain the BBC's longwave frequency until 1988, when it was moved slightly to 198 kHz. Mediumwave transmitters were used to augment coverage.
The Regional SchemeEdit
On 21 August 1927, the BBC opened a high power mediumwave transmitter at the Daventry 5GB site, to replace the existing local stations in the English Midlands. That allowed the experimental longwave transmitter 5XX to provide a service programmed from London for the majority of the population. This came to be called the BBC National Programme.
By combining the resources of the local stations into one regional station in each area, with a basic sustaining service from London, the BBC hoped to increase programme quality whilst also centralising the management of the radio service. This was known as The Regional Scheme.
The local transmitters were gradually either converted to a regional service relay or closed entirely and replaced by high power regional broadcasts. Some local studios were retained to provide for programming from specific areas within each region. Most transmitters also carried the BBC National Programme on a local frequency to supplement the longwave broadcasts from 5XX, initially these were on three separate frequencies in order to minimise interference. As the regional network expanded these were synchronised with Brookmans Park.
Upon the outbreak of World War II, the BBC closed the Regional and National Programmes and replaced them with a single channel known as the BBC Home Service. The transmitter network was synchronized on 668 and 767 kHz. Each transmitter group would be turned off during an air raid to prevent their signals being used as navigational beacons and listeners were required to retune to a low-powered single-frequency network on 1474 kHz.
On 29 July 1945, within 12 weeks of VE Day, the BBC reactivated the Regional Programme, but kept the name "BBC Home Service". The National Programme was also reopened under a new name as the BBC Light Programme.
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