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UK Broadcast Transmission |
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ON THE HOME FRONT - AM RADIO IN SOUTH-EAST ENGLAND
During the Second World War, a serious conflict of interests arose regarding broadcasting. On one hand, the population had to be kept informed of the current situation, especially with the threat of invasion across the Channel. On the other hand, broadcast transmitters also made excellent sources for Radio Direction Finding (RDF) by the Luftwaffe.
The problem was resolved to a great extent by using synchronous groups of transmitters. The high power MF transmitters were split into two groups of four, each group having its own frequency. All four transmitters in the group broadcast on the same frequency, thus providing a radio service with a much reduced chance of it being of use to the Luftwaffe.
The stations were all under the control of Fighter Command who, if enemy aircraft approached one of the stations, would order it to be closed down. (In fairly close proximity RDF could be used). With the common frequency working, listeners in the area could still hear the Home Service from one of the other stations in the group, though at a reduced level. As air-raids increased, it was sometimes necessary to close three out of the four transmitters in the group; in this case the fourth was also closed, again to deny an RDF source.
To cope with this problem, the "Group H" stations were built. This group consisted of 61 transmitters, with an output of 50-100W in towns having a population of 50,000 or more. All operated on 1474kc/s and were, if possible, built adjacent to a tall structure (water tower, chimney etc) so that conventional masts were rarely used to support the wire aerials. Each station was staffed 24 hours a day by Engineers, Technical Assistants (Female) and Youths (Transmitters). Although technically under the control of Fighter Command, the stations were to close down independently, if an air raid was in progress or (Especially along the South Coast) "...if local gunfire is heard".
The frequencies of all the MF stations had to be maintained within very fine limits to prevent beats with nearby stations. A system of audio tones derived from the group "Master" frequency, was line fed to all the group, multiplied, then compared with the station output. Drives were then adjusted for zero beat. Later, in 1943, a single 1kc/s tone was distributed to all stations from a master crystal oscillator in BH and applied to a CRT for a visual display of the frequency error.
In the late forties and early fifties, a number of small MF stations were built; some to provide the new Third Programme and some to provide a better Home Service.
Also, at this time, more and more powerful transmitters were coming into service in Europe some of which made domestic MF listening a much more difficult operation. All of the small Third programme Transmitters worked as a Synchronous Group on 1474kc/s.
In some cases, Group H sites were used. Brighton MF started at the Group H site in September 1946, then moved to the present site (with a 1kW transmitter rather than the 100W Group H unit) and entered service on 21-Nov-1948. The W.E. transmitter was replaced in Oct '49 by a prototype multi-unit transmitter manufactured by Wayne Kerr Laboratories. This consisted of ten 150W units, each having a PSU, modulator and modulated amplifier. This system was found to be unpracticable but the experience gained was put to use in the design of the MWT BD210 660W transmitters, used in groups of three, which became fairly standard in later years. When other services were required, some of the three-unit sets were split to provide more than one service from a site. Folkestone, for example, when Radio One started in 1967, had one of the three Radio Two units retuned for the new service.
During the late 1940s-early '1950s, the transmitters were all manned (but only for one hour a day) by a "Technical Assistant in Attendance". At other times, the TAiA was expected to monitor the station, using a modified receiver with a carrier fail alarm. Each station was also provided with a Telephone Indicator Panel (TIP) the first form of the present TM1M. When a major fault developed, the area Transmitter Maintenance Team, based at Bartley near Southampton, would attend. The Bartley Team was only the third to be formed (C1953) and would visit each station for routine maintenance every four to six weeks. (Bartley's patch covered the South of England and South Wales!)
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Bartley carried the West of England Home Service to Southampton on 1457khz 206m in a synchronous chain with Clevedon, Brighton, Bexhill and
Folkstone. I believe the power was 10kW.
All that remains is the concrete block of the mast base and the anchor points. The introduction of Radio 4 UK on Long Wave spelt the end of the station. |
Of the six "Group H" stations in South-East England, two survived into the 1970s. Ramsgate was used as an R4 "filler" until the big MF frequency change on 23- Nov-1978 when it was closed down, dismantled, and the site returned to the Water Board. Gillingham was resurrected for a time to serve as the Radio Medway (now Radio Kent) MF transmitter, before the move to Hoo in 1976.
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Home Service AM coverage in the South-East of England |
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Bexhill, Brighton, Folkestone, and Ramsgate all used the BD210s until, in the period 1979 - 1984, they were either closed down (Ramsgate) or re-engineered with Solid State transmitters.
Bexhill | Brighton | Clevedon | Folkestone
Home, Light and Third - AM radio in the early Sixties
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