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This huge transmitting station sends an embedded in-audible signal hidden within BBC Radio 4. The 500kW signal enters over 800,000 homes across the UK and controls their electricity. Two old and irreplaceable valves make this happen, but they could die at any point, and the BBC is looking to move away from longwave.
So as of the 30th of June 2025, the longwave radio signal that controls the hot water and heating on and off timings for over 800,000 of these on electricity meters will come to an end. Radio Teller Switch came about during the 1980s as part of a set of energy management projects initiated by the Electricity Council in the UK. The idea of using existing national broadcasting infrastructure for sending teller switching
signals was considered back in 1964. Following the success of extensive trials which started in 1979, the relevant authorities approved radio teller switching transmissions on the BBC's National 198 KHz longwave broadcasts. The system was developed by BBC Research and Development in 1984 and in 1987, it won a Queen's Award for Technology for the Radio Teller Switch system.
Full operational radio teller switching facilities became available in 1984, which have supported electricity demand management for over 40 years. Radio teller switches in device used primarily to allow electricity suppliers to switch large numbers of electricity meters between different tariff rates by broadcasting an embedded signal in everyday radio broadcast signals.
In simple terms, a radio signal is used to switch certain electricity meters between peak and off-peak rates. It has also been used in multi-rate meters to support customers who rely on electricity for heating and hot water such as those using electronic storage heaters, panel heaters or immersion heaters. The most common type of teller switch has a 24 hour clock and a memory that stores received
programs or messages for 24 hours. These programs or messages are sent within the BBC Radio 4 broadcast signal from Joy Twitch on 198 KHz. An important condition of the system's approval was that radio teller switching data couldn't impair the reception of BBC Radio 4. Both services remain separate as the program's sound amplitude modulates the radio carrier
wave while a data signal representing the encoded messages phase modulates the carrier, but perhaps are making things sound more complicated. In simple terms, the embedded signal does not interfere with the BBC Radio 4 signal. I'll explain how in a second.
The system basically comprises of user terminals and modems, the central teller switch control unit or CTCU, the LF data system, the 198 KHz BBC Radio 4 transmission and the radio teller switching receiver controllers or RCs. Each user of the system, the electricity distribution networks operator and electricity transmission
network operator has a unique set of codes enabling them to address only their own block of meters and switches. The CTCU processes and forwards their switching codes to the BBC message assembler at Crystal Palace. Here the electricity industry codes are combined with the instructions from other users of the service and centre three transmitters. The main transmitter at Joy Twitch outputs 500 kW and can reach most parts of the UK while
two smaller transmitters located at Westaglan and Burhead cover Scotland and Northern Ireland. 30 messages are transmitted per minute, each message having 50 bits of data. 18 of these bits are taken up by a BBC header and cyclic redundancy checktail. 32 bits are available for data. There are two message types, command or immediate which has a priority broadcast and on receipt
immediately sets a teller switch receiver controller internal switches to required status, overriding any program status. There's also program messages which contain updates or refreshes the operating program stored within a teller switch. The serial PSK data that contains the messages runs at 50 symbols per second. Manchester coding is used and this is what preserves the integrity of the BBC Radio 4 transmission
for users of frequency standard. The resulting data stream is at 25 bits per second. Manchester coding is a special case of binary phase shift king. Teller switches are widely used to switch consumer appliances on and off to make use of cheaper tariffs such as Economy 7 and Economy 10. Economy 7 is a differential tariff provided by electricity suppliers that uses base load
or minimum level power generation to provide cheap off-peak electricity during the night. Economy 10 is named because the corresponding electricity plan offers 10 hours of off-peak access during a 24 hour period. It was designed to reduce the electricity cost of overnight electric heating and serves a similar purpose to Economy 7. In the event of a transmitter failure, the teller switch follows the previously received
program. In the event of a power-cut, a temporary fallback program takes over until the next relevant signal is received. The effects of any random noise or interference obliterating the signals are overcome by routine broadcast of data messages. By the 30th of June 2025, the Radio Teller switch service is supposed to end. After a long, trusted and largely reliable service, the BBC is continuing to migrate
to all of its programs previously transmitted over longwave onto more modern digital and online media platforms. The BBC has previously announced that it's intending to switch off the radio for longwave transmitters as they're now at the end of their useful life and very few listeners now use longwave according to them. The aging transmitter at Joyt which relies on valve technology to work and there's nobody
making replacements anymore. It was estimated a few years ago that fewer than 10 spare compatible valves existed in the world and the teach valve had a working life of between 1 and 10 years. In October 2011, the BBC stated that Joyt which transmitter, including Radio 4's longwave service and Radio Teller switch, would cease to operate when one of the last two valves breaks.
The two used at Joyt which are both nearly 20 years old and there are now no spares anywhere in the world and if either breaks, the RTS system will stop working. The switch off will affect energy customers that have an RTS meter in their home and may mean that their heating and hot water supply stops functioning as normal. If you have an RTS or DTS meter, RTS is also known as Dynamic Teller switch service,
you can upgrade to a smart meter. Smart meters are the only technical replacement for RTS meters because they can be programmed to deliver a similar service. You may have seen these antennas all over the place on the edge of housing estates and they are used to talk over radio to your smart meter in much the same way RTS does. There has been continued pushbacks on the end date for this service in recent years.
Several extensions were negotiated between the Energy Networks Association and the BBC from 2019, mainly due to the lack of progress in developing suitable smart meter alternatives. In 2020, SSE, one of the major users of the service began informing its customers that teller switch meters would be withdrawn and replaced with alternative solutions. Since then, there has been a series of extensions with a 2021 deal securing teller switch until
mid-2024. As of October 2024, there were still over 800,000 radio teller switch meters still needing to be replaced and in January of this year, the RTS task force launched an advertising campaign to encourage customers to have their meters upgraded. Off-GEM expects energy suppliers to replace all of these meters by the 31st of March 2025.
The big problem is that energy companies may not be able to roll out that many smart meters by the deadline. Replacing RTS meters with smart meters by the 31st of March means they need to install around 21 and a half thousand meters per day just to RTS customers. Currently they are managing over 9000 installations a day for all customers. Some energy firms have already replaced 75% of their customers RTS meters while others
have only managed 10% according to off-GEM statistics. Because of the slow smart meter rollout, energy firms have agreed several extension details to the RTS with the BBC. This likely that the March 2025 deadline will be extended to, but either way, the days of radio teller switch are certainly numbered.
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