UK Medium Wave and Long Wave Transmitter Closures.

[kalee20]

I agree. That's for 'proper' AM.

But I'd been led to believe that the Droitwich transmitter was using a degree of downward modulation, where the upward modulation peaks were a lot less than the modulation troughs (in effect, the carrier amplitude is decreased at high modulation levels).

In addition, the 100kW : 50kW ratio applies for continuous 100% sinewave modulation. The speech content of Radio 4 is a lot more peaky than that, so the average is a lot less.

It's speculation on my part - but I'd bet the increased power bill due to modulating the carrier, is a small part of the running cost.

The likelihood of the power being turned down for low-data-rate comms signals, of course, could be a big threat, especially as this would result in bigger power savings. And I guess the transmitter wouldn't need to run 24/7 either.

[John_BS]

Yes, you're right.
If we assume the nominal power level has not been backed off, a 500kW Tx with 70% efficiency will consume around 740kW at 40% mean modulation depth.

Now, the BBC AMC system was implemented on AM transmissions some time ago, and for domestic Tx's this was originally set at 3dB maximuum carrier power reduction. Recently, driven by the rising cost of energy, work was done to establish if 6dB would be acceptable, (as was the case historically for SW transmissions). This, I understand, has now been implemented, and with typical program material, should result in around 45 to 50% power saving compared with no AMC.
Note that with 6dB AMC, the peak envelope with 100% mod is equal to the mean envelope of the unmodulated carrier.

[Pfraser]

Re. power reduction and programmes: I presumed that an ERP deemed adequate for the teleswitches would not be sufficient for regular broadcasting. Perhaps programmes will continue, but with a degraded S/N ratio, to 'encourage' listeners to seek alternative sources of R4.

[Pfraser]

The Teleswitch service will end next year. From Energy UK:

Over 900,000 energy customers who currently use the Radio Teleswitching Service (RTS) are being urged to take action to upgrade their meters after it was confirmed that the service will end on 30th June 2025.

[Paul Stenning]

If the transmitter is only used for Teleswitches it may only need to be powered during the period when the relevant signals are being sent, which is probably only an hour or two late evening and early morning. It could be run at low idle power or powered down the rest of the time.

[G6Tanuki]

I don't know the precise way in which the radio-teleswitch data is encoded but I know there are multiple different 'addresses' to which the data can be targetted; some but not necessarily all of these will be asociated with electricity tarriff switching.

Having worked with low-data-rate piggyback systems in the past, the one thing that we always did was repeat the messages over and over again so long as there was the bandwidth - this guarded against loss-of-messages due to propagation, interference, power-failure etc; if the R4LW radio-teleswitch phase-modulated carrier were to run at reduced power _and_ only be transmitted for a short period when there was a tarriff-change to implement, there's a risk that not all devices would get the message.

The French Allouis setup runs the transmitter continuously but at reduced power.

[Pfraser]

The latest LW campaign news, reported at Ydun's Medium Wave Info:

Longwave Campaign Update
The petition has now received close to 3000 signatures!

This is a quick update to let you know how things stand at the moment.
The BBC has confirmed that the LW transmitters will continue to broadcast radio teleswitching time signals used for Economy7 heaters until at least March 2025, following a request from the energy companies. We are told that ‘it is a good assumption’ that LW broadcasts of BBC Radio 4 will continue until this date, but this is not 100% certain yet.
However, separate LW programming is still expected to stop at the end of this month, March 2024. This means that the LW signal will be a simulcast of Radio 4 FM from April onwards.
Most programmes will not change as a result of this. But ‘Yesterday in Parliament’, ‘Daily Service’ and ‘Test Match Special’ are not carried by FM and will therefore become digital only, available via Radio 4 Extra, Radio 5 Extra or online. The BBC don’t seem to be willing to budge on this, despite a reconfiguration of the Radio 4 schedule at the same time that could have seen ‘Daily Service’ at least get a new slot on FM.
The future of the LW band, and iconic Droitwich transmitter, after any potential switch-off remains unclear.
Since cost seems to be the main issue, a cheaper option of installing a ‘solid state’ LW transmitter at Droitwich instead of replacing the valves in the current one has been suggested to the BBC, but they are currently unwilling to pursue this.
Overall, we still have hopefully around a year to continue the campaign. It may be that a change in government, and more signatures on the petition, could help to sway things in our direction.
Do please get in touch with any ideas or questions.

Thanks again for your support,
Dr Tobias Thornes
Campaign To Keep Longwave

I hadn't considered the likely change in government as a factor. Interesting!

[stitch1]

Apologies if this has already been covered in the understandably long thread but I’ve not seen mention of R4 medium wave. Does this service cease with R4 LW or is this already a simulcast of R4 FM and what if any plans are there to turn the MW service off?

Thanks

John

[russell_w_b]

Originally Posted by stitch1

Apologies if this has already been covered in the understandably long thread but I’ve not seen mention of R4 medium wave.

I've been away from domestic MF transmitters since 1997, but BBC R4 MF transmitters up here (Carlisle, Wrekenton) were installed to overcome the 'mush-area' problems caused by Droitwich and Westerglen phasing each other out - maybe Redmoss at Aberdeen on R4 MF was for the same reason for Burghead and Westerglen? - the received signals being about equal roughly along Hadrian's Wall plus or minus twenty miles or so north or south.


There was a mush-area correction antenna installed at the BBC Sandale TV/VHF transmitter which was linked to Droitwich or Westerglen (can't remember which) to correct any phasing error but think it fell from use years ago.

The feeds to the MFs were same as those to the LFs. I imagine these R4 MF sites will go when the LF goes. I can't realistically see these small 1kW MF sites being kept alive when the main transmitters are shut down.

[russell_w_b]

Originally Posted by G6Tanuki

I don't know the precise way in which the radio-teleswitch data is encoded...

Seen this?

[winston_1]

Originally Posted by Pfraser

Since cost seems to be the main issue, a cheaper option of installing a ‘solid state’ LW transmitter at Droitwich instead of replacing the valves in the current one has been suggested to the BBC, but they are currently unwilling to pursue this.

And what has that got to do with the BBC who no longer own the transmitters since Birt sold them off?

[paulsherwin]

The BBC pay Arqiva for transmission facilities. Arqiva would happily commission a new LW transmitter if the BBC would pay for it - in fact, this would be relatively cheap given the number of perfectly good modern AM transmitters being decommissioned around the world. However, we all know that the BBC is under great financial pressure, and senior management doesn't see any form of linear broadcasting as a long term priority, let alone LW AM.

[Paul Stenning]

Someone shared this on the Facebook group which seems to confirm what has been said in recent posts here https://rxtvinfo.com/2024/end-of-an-...wave-reprieve/

[emeritus]

None of the BBC announcements on Radio 4 that I have heard have mentioned the possibility of using Freeview on your tv as an alternative to buying a digital radio.

[russell_w_b]

Originally Posted by stitch1

Apologies if this has already been covered in the understandably long thread but I’ve not seen mention of R4 medium wave.

https://radiotoday.co.uk/2024/03/dat...e-frequencies/

[stitch1]

Well that’s that then, thanks for the info.

John

[raditechman]

If you read post 213 and open the link posted by Paul you will read, near the end of the article, that the Medium Wave services of Radio 4 will shut down on 15th April, so not long to go.

John

[HamishBoxer]

Radio 4, it was stated by a BBC person is due to stay on till at least 2025. Needed for time switches and emergency devices etc. Sorry if I have already missed this earlier.

[roadster541]

As the last day of R4 MW is nearly here, does anyone know what the expected times of shutdown of the transmitters will be? The links in previous posts say it will end by 15th April. I would like to listen to the very end of my local 756kHz broadcast as I have been a regular listener to it for a long time. I was in Plymouth a couple of days ago and had good reception on the car radio of R4 on 756 which is around 50m from the transmitter.
Rod

[murphyv310]

Recent closures occurred at 12 noon with no warning. Whether the BBC will be any different is anyone's guess