Scrap the LW radio?

[maby]

Good question, happy to be corrected, but I would guess each would transmit on a slightly different frequency?

This is done on Radio 4 VHF FM in London, which is mostly covered by Wrotham Mast, but Wrotham can't reach a dip in the ground in SW London, which is served by Crystal Palace mast, and the two are on slightly different freq's, although nominally the same (93.3 MHz?).

Modern broadcast receivers jump automatically so the difference is masked (eg a car radio).

I'm only a humble 2E0 so don't take it as gospel..but not too far off the mark..

Not at long wave frequencies, I would think - 20 or 30 khz is nothing at VHF frequencies and the AFC in the receiver probably would cover it up, but R4LW is running at 198khz - that's only 10 times the upper limit of audio frequencies - and AM - AFC does not work.

 

[Minchsailor]

The BBC said several years ago that they had no source for the high power LW transmitter valves, and when they blew, that would be the end of LW in this country. But I can't believe they couldn't be custom made quite cheaply. They're simple devices, and all the requisite fabrication skills are readily available.

When I was a lad, (many, many moons ago...) I had a job in the research labs of a large electronics company building low light TV pickup tubes - not a world away from large transmitter valves, but arguably more complex. Yes, it is reasonably easy; a bit fiddly, and you have to know what you are doing, but not impossible.

I believe there is a Danish company that could supply a new transmitter module for LW virtually off the shelf.

 

[bedouin]

Good question, happy to be corrected, but I would guess each would transmit on a slightly different frequency?

This is done on Radio 4 VHF FM in London, which is mostly covered by Wrotham Mast, but Wrotham can't reach a dip in the ground in SW London, which is served by Crystal Palace mast, and the two are on slightly different freq's, although nominally the same (93.3 MHz?).

Modern broadcast receivers jump automatically so the difference is masked (eg a car radio).

I'm only a humble 2E0 so don't take it as gospel..but not too far off the mark..

LW is not like VHF in having multiple frequencies - but googling shows the other 2 transmitters are much lower power so must be used to fill in gaps caused by local geography

 

[MM5AHO]

They used to be all three transmitters on the same freq. It was only during announced routine maintenance that a distant listener like I was, could tell which one they were receiving. They were all on 198kHz. I didn't notice any interference, nor time difference (distance is a bit shorter from west Iceland to Scotland than to Droitwich).
Even though the two Scottish TX were (still are) lower output power, they were what I received best. I don't think there's any deliberate directionality in antennas.

 

[Yellow Ballad]

Thanks all, vhf holes and poor mobile internet is a good reason to keep LW.

I think I'll replace the fixed with a portable one though.

 

[lw395]

How can they transmit on the same frequency from 3 transmitters? Wouldn't that cause interference effects in the signal?

Because the wavelength is 1500m, the interfence effects are easier to predict and manage.
I'm not sure if the two slave transmitters are polarised differently from Droitwich?

 

[maby]

Because the wavelength is 1500m, the interfence effects are easier to predict and manage.
I'm not sure if the two slave transmitters are polarised differently from Droitwich?

I seriously doubt that - with a wavelength close to a mile, antenna polarisation is a bit academic - antennae are supposed to be a significant fraction of a wavelength above ground to perform in a predictable way!

 

[Giblets]

IIUC if long wave goes down there will be a lot of leccy customers (amongst others) who will suddenly find that their Economy Seven meters won't switch to low price juice not to mention all those with radio controlled clocks.

 

[maby]

IIUC if long wave goes down there will be a lot of leccy customers (amongst others) who will suddenly find that their Economy Seven meters won't switch to low price juice not to mention all those with radio controlled clocks.

Radio controlled clocks get their signal from another transmitter - 60khz which is ultra-long wave and purely for a time signal. Economy 7 meters did get a timing signal from the Radio 4 transmission, but I was under the impression that that had died out a long time ago. We are all supposed to be switching to smart meters over the next few years - they sync up over the internet via 3G.

 

[Yellow Ballad]

Economy 7 meters did get a timing signal from the Radio 4 transmission

Is that why you sometimes get odd noises from R4, like a beep or a split second sound as if someone was speaking over the reporter?

 

[maby]

Is that why you sometimes get odd noises from R4, like a beep or a split second sound as if someone was speaking over the reporter?

I'm afraid I don't know how the time signal was encoded - not something I've ever needed to understand. I'm not convinced that it is still broadcast anyway - it predated the 60khz MSF time service which is now the official way of synchronising time along with GPS.

 

[Giblets]

As recently as September 2015 the signal was sent out with the R4 LW broadcast.

"Economy 7 switching signals are sent to dual rate meters over the radio 4 long wave carrier - a low data rate phase modulation is 'hidden' under the normal AM speech signal. This transmits coded time information every minute and also proprietary "meter switching" data blocks for different DNOs teleswitches and meters. "

 

[Goldie]

What sort of range can you usually pick up R4 on LW?

At night, I've picked up the shipping forecast (the night one is/was the only one to include sea area Trafalgar) from the Straits of Gibraltar.

 

[Goldie]

Really what I should ask is what is the benefit of a MW/LW radio apart from the R4 shipping forecast?

It's there for Test Match Special - the shipping forecast is a bonus!

Seriously though, my long wave radio has suffered a catastrophic accident (it was a Sony SW100 and no longer made). Any suggestions for a sensibly priced portable that works EFFECTIVELY on LW would be much appreciated. I tried a Tecsun (which came recommended) but it was nowhere near as good as my tiny old Sony was in the same location. I've been offered a Sony 7600GR - any LW user experiences out there please?

 

[Goldie]

Tuning in last year reception in Falmouth seemed poor - have they economised on the transmission power? The whole point of LW was good long distance reception.

LW reception is poor in that area BUT, R4 LW is re-transmitted by 2 MW sites: Redruth (for W. Cornwall) on 756 kHz and Plymouth (W. Devon/E. Cornwall) on 774 kHz.

 

[jeanpaulcopie]

At night, I've picked up the shipping forecast (the night one is/was the only one to include sea area Trafalgar) from the Straits of Gibraltar.

Quite right, that's why if you didn't have Navtex you can pick up that forecast in Trafalgar aerea, just before BBC World Service. So still usefull!

 

[machone]

I have a Tecsun and it is worth the bilge space - very small. With iPad and relevant lead(I use an apogee one converter) you can turn your Radio/iPad/iPhone into a navtex receiver. Get the navtex app, plug in your iPad via the apogee or similar and let it listen in silence if you want. At the published times on 490 and 518 you will get decoded Navtex. Very handy. This in addition to a backup forecast receiver. Do not chuck or buy a smaller one.

 

[john_morris_uk]

Both China and Russia still manufacture thermionic valves. Presumably not the exact ones used by Droitwich. The skills and techniques are not disappearing.

What appears not to be known by many on here is that Droitwich 198 kHz is extremely accurate and can be used to phase lock a local source to provide accurate time or frequency measurement.

The Droitwich 198 kHz signal is broadcast by a BBC Radio 4 transmitter with a carrier power of 400 kW. The Droitwich station uses rubidium frequency standards and the fractional frequency offset typically observed is less than 10e-11 over a one day averaging period. For nothing one can lock a frequency standard to this very accurate signal.

 

[Deleted member 36384]

..... Russia still manufacture thermionic valves. ....

A bass player for Jimi Hendix bought a factory in one of the former Russian countries that makes thermionic valves. He bought them for hi end amplifiers and when he heard the factory was being closed he stepped in. The townsfolk were so grateful that later they defied mafia threats who tried to burn the building down to get the land, by surrounding the building and not letting the mafia near it. Interesting TV programme about it all.