Beginning in the early 1980s, UK homes could have electrical meters installed with a radio teleswitch attached. These switches listened for a 198 kHz signal from the BBC's Radio 4 Long Wave service, primarily broadcast from the powerful Droitwich Transmitting Station. These switches listened to 30 messages per minute, waiting for a certain 50-bit data packet to arrive that signaled that electricity was now at cheaper, off-peak rates ("tariffs" in the UK).

With this over-the-air notice, homes that bought into Economy 7 or Economy 10 (7 or 10 hours of reduced-price power) could make use of ceramic-stuffed storage heaters that stayed warm into the day, prepare hot water heaters, and otherwise make use of off-peak power. How the electrical companies, BBC, and meters worked together is fascinating in its own right and documented in a recent video by Ringway Manchester (which we first saw at Hackaday). https://hackaday.com/2025/04/10/farewell-economy-7-a-casualty-of-the-long-wave-switch-off/

But BBC Radio 4's Long Wave transmissions are coming to an end, due to both modern realities and obscure glass valves.

Two rare tungsten-centered, hand-crafted cooled anode modulators (CAM) are needed to keep the signal going, and while the BBC bought up the global supply of them, they are running out. The service is seemingly on its last two valves and has been telling the public about Long Wave radio's end for nearly 15 years. Trying to remanufacture the valves is hazardous, as any flaws could cause a catastrophic failure in the transmitters.

Rebuilding the transmitter, or moving to different, higher frequencies, is not feasible for the very few homes that cannot get other kinds of lower-power radio, or internet versions, the BBC told The Guardian in 2011. What's more, keeping Droitwich powered such that it can reach the whole of the UK, including Wales and lower Scotland, requires some 500 kilowatts of power, more than most other BBC transmission types.

As of January 2025, roughly 600,000 UK customers still use RTS meters to manage their power switching, after 300,000 were switched away in 2024. Utilities and the BBC have agreed that the service will stop working on June 30, 2025, and have pushed to upgrade RTS customers to smart meters. //

Arstotzka Ars Scholae Palatinae
8y
970
Subscriptor++

Taunted Happy Fun Ball said:
Seems like the obvious solution would be for the regulator to decree that any customer using an older meter following the shutoff will be billed at the off-peak rates for all usage.

Then watch the utilities fall all over themselves to deploy updated meters.

It's rare you can have a technological solution to a people problem, but here it is -- the last transmission before shutdown can be "switch to cheap rates". The utilities will figure it out, after all, because it might cost them money. //

jvok Smack-Fu Master, in training
3y
7

plectrum said:
This is the BBC conveniently lying because it suits them. Nautel recently-ish (2017) installed a 2MW solid-state transmitter for Antenna Hungaria on 540kHz. Their NX400 system is based on stacking phase-locked 25kW modules feeding into a combiner - just buy as many modules as you need. 600kW is no problem - at 90% efficient they're much more efficient than vacuum tubes (50-60%).

I think the bottom line is the BBC just doesn't want to spend the money, on either upgrading the transmitter or on the power bill. Which is fair enough - LW reception is only getting worse given the amount of RF smog from power supplies nowadays so there aren't so many listeners out there any more - but they should own up to it.

I completely buy the idea that the transmitter needs replacing (its 40 years old after all), and that the limited number of listeners left on longwave doesn't justify the expense. It fits with the BBCs and other broadcasters pattern of closing down other legacy services over the last few years (e.g. the local radio AMs). The content broadcast on 4LW is the same as you get on Radio 4 FM and DAB now anyway, the opt-outs (e.g. for cricket coverage) were discontinued a few years back. Hell, how many people even still own a longwave radio?

I get a serious case of Gell-Mann amnesia reading that Guardian article though. I get the impression that the author heard some off-hand comment about the transmitter using valves and decided to turn it into some "OMG critical BBC infrastructure is still using old school valves" story. Even calling them glass valves (which isn't accurate) to invoke images of us all gathering round the wireless like its still the 1930s. When in reality high power transmitters using valves is pretty normal and they're still manufactured today. But of course the public doesn't know that so it still makes for a good story. //

video series on how the 900MHz system in the US works.
https://youtube.com/playlist?list=PLYlhncU2MojDY9gxU36pxNVkiylGGcbwq&si=D0j-q_xzW_uuYAQp