Radio 4 Long Wave Switch Off

[tom66]

I tuned into it this morning to confirm it's still broadcasting the retune message and it is. This is really annoying because it's wasting energy. Listeners have been given plenty of warning the long wave service was going to end and how to receive Radio 4. There is no need to keep it on, just to broadcast a retune message. If they're willing to use the energy, they should have delayed the shutdown. The BBC keep on banging on about climate change and how we should all reduce our energy consumption. They are complete hypocrites.

As far as I know, the 198 kHz carrier also transmits a low-rate digital data signal containing things like time information and other control data, and it's used by some electricity meters and other devices.

I actually learned about that from this discussion, so I haven't tried decoding the data stream myself yet. That may be the reason they're keeping the transmitter on for now while discontinuing the Radio 4 audio service.

In this way, they are still maintaining the service for meter infrastructure, while effectively removing the "free add-on" in the form of the broadcast audio program.

The 198kHz frequency was regulated by a caesium reference, which meant it could be used by some to generate a timing reference.  Nowadays GPS time sources provide good alternatives.  There's a digital data carrier there that provides time and date info used by timeswitching meters.  GPS and newer smart meters replace this information source.

Wouldn't they still save power by completely shutting down the audio, leaving it as a pure data station? Otherwise they should have left the audio on.

As far as I understand the power consumption of AM transmitting modulated audio and no audio is pretty much the same.  Sure it will use more power for higher amplitude but audio is an AC signal, so in the net it should balance out, ignoring any nonlinearity.  Happy to be corrected.

[SteveThackery]

Yes, that's exactly why I updated original post, I'm not even sure whether it's worth discussing.

Sometimes I wonder whether it's better to warn people about a possible future so they have a chance to prepare, or to leave them with their peace of mind if there's little they can do to change the outcome. I honestly don't know which approach is kinder. Unfortunately, I've seen that many people struggle to accept reality as it is, and for some, the psychological impact can be overwhelming.

We're grownups - give it to us straight. I, for one, would really appreciate it.

[Zero999]

I tuned into it this morning to confirm it's still broadcasting the retune message and it is. This is really annoying because it's wasting energy. Listeners have been given plenty of warning the long wave service was going to end and how to receive Radio 4. There is no need to keep it on, just to broadcast a retune message. If they're willing to use the energy, they should have delayed the shutdown. The BBC keep on banging on about climate change and how we should all reduce our energy consumption. They are complete hypocrites.

As far as I know, the 198 kHz carrier also transmits a low-rate digital data signal containing things like time information and other control data, and it's used by some electricity meters and other devices.

I actually learned about that from this discussion, so I haven't tried decoding the data stream myself yet. That may be the reason they're keeping the transmitter on for now while discontinuing the Radio 4 audio service.

In this way, they are still maintaining the service for meter infrastructure, while effectively removing the "free add-on" in the form of the broadcast audio program.

The 198kHz frequency was regulated by a caesium reference, which meant it could be used by some to generate a timing reference.  Nowadays GPS time sources provide good alternatives.  There's a digital data carrier there that provides time and date info used by timeswitching meters.  GPS and newer smart meters replace this information source.

Wouldn't they still save power by completely shutting down the audio, leaving it as a pure data station? Otherwise they should have left the audio on.

As far as I understand the power consumption of AM transmitting modulated audio and no audio is pretty much the same.  Sure it will use more power for higher amplitude but audio is an AC signal, so in the net it should balance out, ignoring any nonlinearity.  Happy to be corrected.

Of course that's true, but then how do they transmit the data, without interfering with the audio?

Something doesn't quite add up.

[tom66]

Of course that's true, but then how do they transmit the data, without interfering with the audio?

Something doesn't quite add up.

Phase modulation of the carrier.  This is ignored by the AM audio decoder since it is sensitive to amplitude only. 

[G0HZU]

For regular AM modulation it definitely requires more power input when modulated and this is most noticeable at high modulation depths. However, in the case of R4 on 198 kHz LW I think they do a trick with the carrier level when the modulation depth is high. It looks to me like the carrier sags during these high depth events. I don't know why this carrier sag trick is done but it has been like this for a long time and it may be to reduce stress on the transmitter components  and/or to improve efficiency slightly. There must be a way to do it to prevent excess distortion/spreading and it appears to me to be similar to having compression added. Maybe someone else knows about this in more detail?

I can see this 'compression' effect in the time and frequency domain on my test gear here. If anyone wants to see this then be quick because I think the transmitter may be turned off on Tuesday. Tuesday 30th June is the anniversary of the start of the phasing out of the Teleswitch data and a couple of energy websites have claimed that this gets turned off this Tuesday. Presumably, the carrier will get turned off at the same time and this will end both the BBC looped signal and the Teleswitch service.

[G0HZU]

Many years ago I posted up a youtube video showing the time pips on R4 LW using an old Tektronix RSA3408A RTSA. This shows the carrier sag effect fairly well but it's best viewed in the time domain on a suitable scope. The RSA3408A RTSA is very dated now but it did OK here I think.



You can see the attack and decay time is different for the change in the carrier level. It recovers slower than it sags. Many other AM stations (eg on medium wave) don't do this and the carrier level remains (essentially) static during modulation peaks.

[G0HZU]

One thing to bear in mind is that there has to be some sort of limit to the modulation dips because otherwise this will compromise the Teleswitch phase modulated data. The modulation can’t dip too low in amplitude in other words. So when viewed in the time domain, the AM modulation isn’t quite the same as other stations in terms of how low the signal gets on modulation dips. The modulation looks shallower and this is presumably done to protect the integrity of the phase modulated data. The carrier ‘sag’ or compression effect may be part of this. But I can only guess at this.

[radiolistener]

We're grownups - give it to us straight. I, for one, would really appreciate it.

You may feel that anything can be discussed freely, and in some environments a high degree of openness is indeed possible, but this is not universal. In such cases, people use what is called Aesopian language.

[Xena E]

For regular AM modulation it definitely requires more power input when modulated and this is most noticeable at high modulation depths. However, in the case of R4 on 198 kHz LW I think they do a trick with the carrier level when the modulation depth is high. It looks to me like the carrier sags during these high depth events. I don't know why this carrier sag trick is done but it has been like this for a long time and it may be to reduce stress on the transmitter components  and/or to improve efficiency slightly. There must be a way to do it to prevent excess distortion/spreading and it appears to me to be similar to having compression added. Maybe someone else knows about this in more detail?

I can see this 'compression' effect in the time and frequency domain on my test gear here. If anyone wants to see this then be quick because I think the transmitter may be turned off on Tuesday. Tuesday 30th June is the anniversary of the start of the phasing out of the Teleswitch data and a couple of energy websites have claimed that this gets turned off this Tuesday. Presumably, the carrier will get turned off at the same time and this will end both the BBC looped signal and the Teleswitch service.

Very interesting thank you Jeremy. I've never seen any of the technical details of how this was done, but believe that it was by some form of digital feed forward control of the PA stages, the only clue I have for this is once being told that there was a very small modulation delay being introduced so that the output power can be economised, my guess being in effect some kind of sliding bias.

Having seen it done with other smaller installations where the program material is discontinuous and savings no doubt a real advantage. I wondered if it were a similar system, as I'd heard the same 'sibliance' on the transmitted audio from Droitwich on occasions when for some reason the processing failed. 

[Xena E]

We're grownups - give it to us straight. I, for one, would really appreciate it.

It's very bad form to try to goad someone into repeating off topic opinions when you know they have been expressly requested not to make them by administration.

You may feel that anything can be discussed freely, and in some environments a high degree of openness is indeed possible, but this is not universal. In such cases, people use what is called Aesopian language.

Unfortunately history is prone to repeat itself because of human nature, people who have not lived in a repressed society do not believe it will happen to them.

International broadcasting was always considered a valuable tool in getting a message into a foreign territory, for the listener, it was an anonymous way to get a more balanced view of events. No one invests in it any more is what I'm told, strangely though I find that at least one regime is bucking that trend, even paying for new high power transmitters within Europe.

When people feel safe they tend to like to live with convenience, so why would they listen to crackling signals on a broadcast radio when they can just ask a smart speaker to play whatever. It is so attractive to them.

Radio 4 on longwave was a symbolic entity, the long closed down BBC world service transmitter on 648kHz was more of use internationally, just as the VOA transmitter in Botswana was also. Long range broadcast radio is in it's death throes, do I think it's bad? Maybe, can an individual change the situation? No chance! The VHF FM services will follow next.

Don't get me wrong, I don't think it's the be all and end all of the situation, or even a constructive conspiracy, it's just setting up conditions for a perfect storm.

If the worst happens not only will the little frogs be boiled slowly in the pot, but they will get in willingly, it's best to leave them in their happy ignorance.

[Zero999]

Of course that's true, but then how do they transmit the data, without interfering with the audio?

Something doesn't quite add up.

Phase modulation of the carrier.  This is ignored by the AM audio decoder since it is sensitive to amplitude only.

That makes sense, but if it doesn't take that much more to broadcast the audio and the station is needed for data anyway, then they might as well continue to broadcast Radio 4 on it. Now I personally don't care. I've never been a Radio 4 fan, either on long wave or FM. I remember listening to it whilst on holiday in France, back in the 90s, because it was one of the few English stations I could receive to get the news, but now we have the Internet. I can just see the other side of the argument.

[tom66]

That makes sense, but if it doesn't take that much more to broadcast the audio and the station is needed for data anyway, then they might as well continue to broadcast Radio 4 on it. Now I personally don't care. I've never been a Radio 4 fan, either on long wave or FM. I remember listening to it whilst on holiday in France, back in the 90s, because it was one of the few English stations I could receive to get the news, but now we have the Internet. I can just see the other side of the argument.

There are only a few timeswitch meters in parts of the country remaining and there is an ongoing program to replace them for about a decade.  In the absence of received signals these meters will not know if they are in off peak or on peak.  Hopefully they "fail safe" and default to keeping heating on.

I suspect that some do not want to switch away from timeswitched meters due to unfounded fear of smart meters, this may be the kick they finally need.

Unfortunately history is prone to repeat itself because of human nature, people who have not lived in a repressed society do not believe it will happen to them.

International broadcasting was always considered a valuable tool in getting a message into a foreign territory, for the listener, it was an anonymous way to get a more balanced view of events. No one invests in it any more is what I'm told, strangely though I find that at least one regime is bucking that trend, even paying for new high power transmitters within Europe.

When people feel safe they tend to like to live with convenience, so why would they listen to crackling signals on a broadcast radio when they can just ask a smart speaker to play whatever. It is so attractive to them.

Radio 4 on longwave was a symbolic entity, the long closed down BBC world service transmitter on 648kHz was more of use internationally, just as the VOA transmitter in Botswana was also. Long range broadcast radio is in it's death throes, do I think it's bad? Maybe, can an individual change the situation? No chance! The VHF FM services will follow next.

Don't get me wrong, I don't think it's the be all and end all of the situation, or even a constructive conspiracy, it's just setting up conditions for a perfect storm.

If the worst happens not only will the little frogs be boiled slowly in the pot, but they will get in willingly, it's best to leave them in their happy ignorance.

It is far easier to jam a radio signal than it is to block all means of access to the internet, given satellite internet now exists.  For instance look at how Iranians managed to access the internet throughout the various blockades via Starlink, satellite radios and cellular signals across borders.  All Radio 4 gives you is the government-sanctioned take on things; sure, they can be a little critical here or there, but do you really think the BBC will be able to defy an authoritarian state?

[Zero999]

That makes sense, but if it doesn't take that much more to broadcast the audio and the station is needed for data anyway, then they might as well continue to broadcast Radio 4 on it. Now I personally don't care. I've never been a Radio 4 fan, either on long wave or FM. I remember listening to it whilst on holiday in France, back in the 90s, because it was one of the few English stations I could receive to get the news, but now we have the Internet. I can just see the other side of the argument.

There are only a few timeswitch meters in parts of the country remaining and there is an ongoing program to replace them for about a decade.  In the absence of received signals these meters will not know if they are in off peak or on peak.  Hopefully they "fail safe" and default to keeping heating on.

I suspect that some do not want to switch away from timeswitched meters due to unfounded fear of smart meters, this may be the kick they finally need.

My point is, if they have to continue the 198kHz transmission for other services and it doesn't cost much to have Radio 4 on it, then they might as well continue with it, until the 198kHz signal is no longer needed.

Unfortunately history is prone to repeat itself because of human nature, people who have not lived in a repressed society do not believe it will happen to them.

International broadcasting was always considered a valuable tool in getting a message into a foreign territory, for the listener, it was an anonymous way to get a more balanced view of events. No one invests in it any more is what I'm told, strangely though I find that at least one regime is bucking that trend, even paying for new high power transmitters within Europe.

When people feel safe they tend to like to live with convenience, so why would they listen to crackling signals on a broadcast radio when they can just ask a smart speaker to play whatever. It is so attractive to them.

Radio 4 on longwave was a symbolic entity, the long closed down BBC world service transmitter on 648kHz was more of use internationally, just as the VOA transmitter in Botswana was also. Long range broadcast radio is in it's death throes, do I think it's bad? Maybe, can an individual change the situation? No chance! The VHF FM services will follow next.

Don't get me wrong, I don't think it's the be all and end all of the situation, or even a constructive conspiracy, it's just setting up conditions for a perfect storm.

If the worst happens not only will the little frogs be boiled slowly in the pot, but they will get in willingly, it's best to leave them in their happy ignorance.

It is far easier to jam a radio signal than it is to block all means of access to the internet, given satellite internet now exists.  For instance look at how Iranians managed to access the internet throughout the various blockades via Starlink, satellite radios and cellular signals across borders.  All Radio 4 gives you is the government-sanctioned take on things; sure, they can be a little critical here or there, but do you really think the BBC will be able to defy an authoritarian state?

Yes, trust in the BBC has really taking a battering in recent years and it's largely their fault.

[Xena E]

It is far easier to jam a radio signal than it is to block all means of access to the internet, given satellite internet now exists.  For instance look at how Iranians managed to access the internet throughout the various blockades via Starlink, satellite radios and cellular signals across borders.  All Radio 4 gives you is the government-sanctioned take on things; sure, they can be a little critical here or there, but do you really think the BBC will be able to defy an authoritarian state?

A swing, and a miss!

Firstly. To paraphrase what I said for you, the R4 Longwave thing is symbolism of all traditional broadcast radio. It wouldn't have had any real use in spreading either information or propaganda.

Secondly I have no regard for the BBC whatsoever. They who are at best a shower of institutionalised shit, spouting the opine of whatever group of political morons are in power at the time, it has always been thus.

My point is the anonymity that listening to a broadcast radio brings the listener, wheras as soon as you log in to your computer you and what you listen to, watch, read, or buy can be and is tracked.

I didn't mention internet, but as it seems to be what people want to discuss so be it.

In the Afghanistan conflict British personnel were instructed not to use internet connections or mobile phones to contact family because the Taliban had resources to track the connection and identify both caller and recipients. If they can do it so can anyone with inclination and the money for resources.

[tom66]

A swing, and a miss!

Firstly. To paraphrase what I said for you, the R4 Longwave thing is symbolism of all traditional broadcast radio. It wouldn't have had any real use in spreading either information or propaganda.

Secondly I have no regard for the BBC whatsoever. They who are at best a shower of institutionalised shit, spouting the opine of whatever group of political morons are in power at the time, it has always been thus.

My point is the anonymity that listening to a broadcast radio brings the listener, wheras as soon as you log in to your computer you and what you listen to, watch, read, or buy can be and is tracked.

I didn't mention internet, but as it seems to be what people want to discuss so be it.

In the Afghanistan conflict British personnel were instructed not to use internet connections or mobile phones to contact family because the Taliban had resources to track the connection and identify both caller and recipients. If they can do it so can anyone with inclination and the money for resources.

Let's be honest though, the internet is the eventual replacement for services like analog radio.  DAB has had a pretty muted reception, broadcast TV is waning, and FM radio will likely be phased out in the next decade.

And in terms of safety, VPNs exist that provide effectively perfect anonymity.  You can trace what device was using a VPN (maybe) but you cannot tell what that device was accessing.  And with HTTPS transport and DNS over HTTPS, VPN looks no different to any other internet traffic.  This is why China has still not managed to ban VPNs and even countries like UAE which make it illegal to use a VPN can only catch you if they find the app on your phone, etc. 

[tom66]

My point is, if they have to continue the 198kHz transmission for other services and it doesn't cost much to have Radio 4 on it, then they might as well continue with it, until the 198kHz signal is no longer needed.

My understanding is Arqiva/BBC have determined the valve that powers the transmitter is EOL and there are no longer sufficient spares to guarantee a service can be maintained.

Therefore, they are taking the route of advising people well in advance and phasing the broadcast out, which will include the time switch and data channel.

The alternative would be to leave the transmitter running but at some undetermined time in the future it suddenly stops functioning and everyone relying on that service is left in the dark.

Or they could refurbish the equipment at some significant expensive and move to solid state transmitter, but it's not exactly value for money to do so given the small audience.

I think they made the right decision.

[chilternview]

My understanding is Arqiva/BBC have determined the valve that powers the transmitter is EOL and there are no longer sufficient spares to guarantee a service can be maintained.

I suspect this is just an excuse. They could have replaced the transmitter with something modern and solid state. But the real issue is that the listener figures are no doubt very low.

I think they made the right decision.

Only time will tell...

[paul cotter]

As I have previously stated all high power thermionic devices can be rebuilt. Actually that may not be !00% true: all powerful glass thermionic devices can be reconditioned- I don't know about ceramic valves(tubes) as I never tried.
On the subject of carrier dip on modulation I would have thought that distortion would result? There were in the past schemes to produce enhanced positive going modulation while maintaining negative excursions <100% and although they never caught on I'm sure distortion would result. In the 80s in the US audio processors were all the rage on AM(and FM) and maybe they still are. A common one was the Orban Optimod and this could seriously raise the subjective loudness by clipping and a multiband compressor. Orban stated that their processor could raise positive going modulation to 125%, with the proviso of the tx being able to, and I always found this to be dubious as it would require DC coupling throughout after the processor. Another radio engineer that I was discussing this point with suggested that such a scheme would be pointless as any possible gain would be lost without the use of a synchronous detector- synchronous detectors were not common in that era.

[G0HZU]

I'm not sure how they manage the distortion issue but it may involve some pre-processing to minimise spectral spreading. To show the R4 signal in the time domain, I upconverted the signal to 10.7 MHz and fed this to an old Hameg analogue scope via a buffer amp and a wide crystal filter. I think an analogue scope is the best choice here. A digital scope (at least the ones I have here) can't deliver the same quality here.

The result is as below. You can immediately see that the modulation peaks never seem to go much past 50% but there is definitely some carrier sag and recovery each time there is a pause in the speech. The amount of sag (and recovery rate) seems to depend on the audio so this makes me think there is some processing involved. It does seem to be similar to compression in some ways but it isn't as simple as just adding compression.

It's also possible to see the modulation never dips enough to cause a significant loss in signal level and this may be done on purpose to preserve the integrity of the RTS Teleswitch (phase modulated) data.

When viewed in the frequency domain on the RSA3408A there is some obvious spectral spreading (beyond the +/- 5 kHz BW) on the strongest voice peaks but it isn't at a significant level IMO.

[G0HZU]

In case anyone still can't see this carrier sag effect, then have a look at the start of the video and keep a mental note of the level of the unmodulated carrier. Then watch the whole video and note how high the highest peaks are and also how low the lowest peaks are. They are roughly in the range of the red and blue arrows in the image below. This is not symmetrical around the level of the unmodulated carrier so something is clearly going on here in terms of carrier level control vs modulation depth.

You can also see a few places in the video where the carrier sag recovers during pauses in the speech. I think this may all be managed by using pre-processing of the audio and some form of carrier level control that depends on the modulation depth etc.

[paul cotter]

Thank you very much for those scope shots. If I had been shown these and asked for a diagnosis I would have said poor DC regulation due to the modulation loading the psu! I have often seen such waveforms on a poorly designed tx. The time constant is long enough to discount overt distortion.

[G0HZU]

Thanks. I agree it does look similar to a PSU regulation (HT?) regulation issue but it has been like this for many years now. I've added another video below where I look in the frequency domain with the old RSA3408A analyser as I still have it here.

The audio in the video isn't great as I've used a medium sized portable radio to receive the signal (for sound) but R4 LW never sounds that great on my other receivers. You might be able to detect some of the sibilance that Xena E was referring to. There is some spectral spreading visible when this happens.

The transmitter has been prone to this sibilance issue for many years and sometimes it gets really bad and the transmitter has to be taken off air and serviced. I've got numerous data recordings of R4 on LW using the RSA3408A and these date back to 2016 at least. Some of them were taken when the sibilance was particularly bad. I'm not sure where they all are now but I've found a few of them still stored on the RSA3408A HDD.

They are in a format that can be played back on a vector sig gen like an Agilent ESG E4433B or E4438C (as long as it has a dual arbitrary waveform generator fitted) and this means the original RF signal can be replicated and received on a LW receiver or whatever frequency the sig gen is set to. I hope the video below is interesting to a few people. It shows the carrier sagging on modulation peaks and shows some spectral spreading in places. This is the real R4 signal taken off air (today) via a screened loop antenna rather than something re-created via a vector sig gen.

[SteveThackery]

....... but if it doesn't take that much more to broadcast the audio and the station is needed for data anyway, then they might as well continue to broadcast Radio 4 on it.

We seem to be missing an important point. The BBC doesn't own the 198kHz transmitter; it's owned by Arqiva. The BBC pays Arqiva to transmit Radio 4 on 198kHz. While the exact cost of the contract isn't published, the best estimate seems to be around £6 million per year. So the BBC is saving around £6 million per year as a result of the R4 long-wave shutdown.

Presumably there is a different contract, with a different customer, for the data transmission.

[tom66]

Radio Teleswitch Signal is paid for by electricity suppliers (retailers).  Cost isn't published.
https://utilityweek.co.uk/energy-suppliers-to-bear-full-cost-of-rts-service/

Arqiva also runs the 420MHz band radio service for smart meters in the North of England which is widely reported by rural users to be "absolutely rubbish".

[radiolistener]

....... but if it doesn't take that much more to broadcast the audio and the station is needed for data anyway, then they might as well continue to broadcast Radio 4 on it.

We seem to be missing an important point. The BBC doesn't own the 198kHz transmitter; it's owned by Arqiva. The BBC pays Arqiva to transmit Radio 4 on 198kHz. While the exact cost of the contract isn't published, the best estimate seems to be around £6 million per year. So the BBC is saving around £6 million per year as a result of the R4 long-wave shutdown.

Presumably there is a different contract, with a different customer, for the data transmission.

£6 million sounds like a rounding error for an organization the size of the BBC.
It feels more like cutting back on office coffee, or even toilet paper, than shutting down a historic national service.