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Radio on LW (long waves)
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<blockquote data-quote="Fisty McB" data-source="post: 1080959" data-attributes="member: 389824"><p>That's a bit of an urban legend - the valves in question can be easily repaired, if required, by sending them back to the manufacturer. It's more the case that the transmitter itself at Droitwich is getting on in years and compared to modern solid state TX's is quite inefficnent. </p><p></p><p>The story of UK nuclear submaries having to check for a signal on 198 kHz as a sort of "dead mans switch" is also very likely to be an urban legend, though given military confidentiality it's something that laymen can neither confirm or deny. However, such thinking assumes that (a) Droitwich cannot fall off the air at all, which is impossible to guarantee (the site is not permantently manned these days) , nor that there are also two other co-channel transmitters for BBC R4 on the same frequency in Scotland which would probably still be on the air. A big kicker however would be the penetration of the depth of the signal into seawater - for the depths nuclear submarines would often dive down to for weeks or even months at a time, LW radio signals would not reach them - while seawater can provide an excellent conductive layer over the top of its surface, it also acts as a very good insulator below it, attenuating signals strongly depending on frequency & depth. VLF frequencies (technically between 3 & 30 kHz, but most usually take it to be up to around 100 kHz) can penetrate to some shallow depths, 20 to 30 metres at best depending on salinity. Lower than this, the only way to communicate to submarines is by using ELF (3 - 300 Hz) which requires a massive set up, but it gives the ability to pretty much reach any submarine on the planet. The USA used to have such a system, but has no been decommissioned, while the UK looked at building their own during the Cold War but didn't go ahead with it. Today, Russia, India & China are the only countries known to have an ELF transmission in place. Of course, because of the limited bandwidths available at such low frequencies, voice can't be used so only data at a low speed rate is transmitted, and it's one way communication only.</p><p></p><p>Other than broadcasting BBC R4's Long Wave Service (i.e. the same as the main service except for a couple of short weekday opt-outs as well as opting out to cover test match cricket), the main use for Droitwich at present is to transmit signals to receive-only electrical metres as a form of time metering e.g. Economy 7 tariffs. As I understand it, the contract for this is due to expire in 2020 but given the large backlog in the roll out of "smart metres", it'll probably continue for a few more years yet. And of course, there's nothing to stop 198 kHz at Droitwich having its audio simply turned off but the carrier left on for its data use - like how 162 kHz is still being used in Allouis, France when France Inter ended its LW transmissions - the BBC R4 LW network is more than just the single TX at Droitwich.</p></blockquote><p></p>
[QUOTE="Fisty McB, post: 1080959, member: 389824"] That's a bit of an urban legend - the valves in question can be easily repaired, if required, by sending them back to the manufacturer. It's more the case that the transmitter itself at Droitwich is getting on in years and compared to modern solid state TX's is quite inefficnent. The story of UK nuclear submaries having to check for a signal on 198 kHz as a sort of "dead mans switch" is also very likely to be an urban legend, though given military confidentiality it's something that laymen can neither confirm or deny. However, such thinking assumes that (a) Droitwich cannot fall off the air at all, which is impossible to guarantee (the site is not permantently manned these days) , nor that there are also two other co-channel transmitters for BBC R4 on the same frequency in Scotland which would probably still be on the air. A big kicker however would be the penetration of the depth of the signal into seawater - for the depths nuclear submarines would often dive down to for weeks or even months at a time, LW radio signals would not reach them - while seawater can provide an excellent conductive layer over the top of its surface, it also acts as a very good insulator below it, attenuating signals strongly depending on frequency & depth. VLF frequencies (technically between 3 & 30 kHz, but most usually take it to be up to around 100 kHz) can penetrate to some shallow depths, 20 to 30 metres at best depending on salinity. Lower than this, the only way to communicate to submarines is by using ELF (3 - 300 Hz) which requires a massive set up, but it gives the ability to pretty much reach any submarine on the planet. The USA used to have such a system, but has no been decommissioned, while the UK looked at building their own during the Cold War but didn't go ahead with it. Today, Russia, India & China are the only countries known to have an ELF transmission in place. Of course, because of the limited bandwidths available at such low frequencies, voice can't be used so only data at a low speed rate is transmitted, and it's one way communication only. Other than broadcasting BBC R4's Long Wave Service (i.e. the same as the main service except for a couple of short weekday opt-outs as well as opting out to cover test match cricket), the main use for Droitwich at present is to transmit signals to receive-only electrical metres as a form of time metering e.g. Economy 7 tariffs. As I understand it, the contract for this is due to expire in 2020 but given the large backlog in the roll out of "smart metres", it'll probably continue for a few more years yet. And of course, there's nothing to stop 198 kHz at Droitwich having its audio simply turned off but the carrier left on for its data use - like how 162 kHz is still being used in Allouis, France when France Inter ended its LW transmissions - the BBC R4 LW network is more than just the single TX at Droitwich. [/QUOTE]
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