Long Wave radio era set to end with Droitwich switch-off

74 pointsposted 11 hours ago
by speckx
(bbc.com)

30 Comments

bilegeek

2 hours ago

IMO, when the last LW transmitter shuts down, the whole band needs to be reallocated to hams. Realistic small-ish antennas are shockingly doable with a capacitance hat, loading coil, and counterpoise.

yakkers

2 hours ago

There’s still a lot of utility stations in the LF/longwave band. Particularly time signals (WWVB in the US, ALS162 in France, DCF77 in Germany, JJY in Japan, etc.) and NDB beacons.

At least in VK/Australia, there’s the 2200 meter band, but it’s quite limited (1W power limit, CW/digital only, 135.7–137.8 kHz).

At the same time, as much as I don’t want the AM broadcast band to die, I’d love an amateur band in the lower/middle part of MF/MW.

bilegeek

an hour ago

> There’s still a lot of utility stations in the LF/longwave band. Particularly time signals (WWVB in the US, ALS162 in France, DCF77 in Germany, JJY in Japan, etc.)

I meant just the broadcast band 148.5-283.5 kHz. (Though I'd love if 2200m and 630m were just a bit wider.)

> and NDB beacons.

Good point[1]. So 148.5-200 kHz in ITU Region 2 (and keep LowFER allowances on 160-190kHz as a consolation prize.)

[1]https://www.dxinfocentre.com/ndb.htm

_whiteCaps_

9 hours ago

Seems like everyone's shutting down radio services. CHU and Weather radio in Canada too :(

mschuster91

8 hours ago

These transmitters consume insane amounts of power. Per Wikipedia, that's 500 kW of rated transmission power for this one [1], so probably a solid megawatt of grid power input.

At 30 ct/kWh, that's 300€ per hour, 7200€ per day and about 2.6 million € a year - for a customer base that is only decreasing.

[1] https://en.wikipedia.org/wiki/Droitwich_Transmitting_Station

yakkers

7 hours ago

Doesn't excuse CHU: two 3kW, one 5kW ERP.

And by the virtue of shortwave propagation, it could be heard across the world. For the past month and a half (from when the news of its impending shutdown was revealed) I was regularly picking it up in Australia right up until the bitter end.

ggm

5 hours ago

Wave skip? (Naieve question)

yakkers

2 hours ago

HF propagates through skywave (most reliably from 5-30MHz), which is where the signal bounces off the ionosphere.

In the MF (AM broadcast) band, you can observe this at night - in Australia I can pick up the 50kW Melbourne ABC station (public broadcaster) at 774kHz with a good radio, just about across the entire country.

In the LF (longwave) band, the earth’s surface and the ionosphere start to behave more like a waveguide than skywave. This is actually more reliable/consistent than even HF, but you need massive transmitting antennas due to the large wavelengths involved.

HF also generally wins for distance covered per watt - despite the massive power of Radio 4 longwave, I’d have no chance of hearing it reach Australia.

reaperducer

8 hours ago

Is that emitted power, consumed power, or effective radiated power? Without knowing that, your power calculations have no meaning.

Radio stations are usually measured by the last of those: Effective radiated power.

You can have a radio station with a 50,000 watt ERP, but running only a 2,500 watt transmitter.

For FM radio stations, it's all about the height of the transmitter above average terrain. For AM, it's about the ground conductivity and frequency.

I once worked at a 1,000-watt AM station that had a signal much larger and clearer signal than the 5,000-watt AM station a few miles away.

I'm not a radio engineer, but I'm sure there are plenty on HN who can correct and clarify what I've written.

BuildTheRobots

7 hours ago

Also bear in mind that Droitwitch is radiating 3 different services. Talk Sport (1053 kHz), Radio 4 (198 kHz) and Radio Five Live (693 kHz).

My suspicion is that this means an exciter and a stack of amps per service, which then go through a two stage combiner and out to the antenna. There might even be a pair of exciters and amps per service depending on redundancy.

The combiners (certainly for FM/DAB/TV services) also cause cumulative attenuation as the signal gets combined each time, so even if all 3 are radiating at the same power, the first in the chain might need twice as much amplification to make up for losses.

edit: MB21 (of course) has some fantastic technical info about Droitwitch: https://tx.mb21.co.uk/gallery/gallerypage.php?txid=1454&page... and there's some great pics here, too: https://www.radiorewind.co.uk/radio1/droitwich.htm

I believe they're still using a pair of Marconi B6042 transmitters (250kW each, in parallel) to provide at least one of the services.

nickcw

9 hours ago

The Droitwich transmitter used to transmit on exactly 200 kHz which I always thought was very cool, but it moved to 198 kHz in 1988 to better harmonize with European stations.

The program was mostly the same as BBC Radio 4 but it used to diverge at certain times of day. I used to be woken up at 5am every day by my parents clock radio with the farming news which was very dull, but easy to sleep through.

mark-r

8 hours ago

Thanks for mentioning the actual frequency. The article says "long wave" many times without specifying what it actually means.

LeoPanthera

7 hours ago

"Longwave", usually written without a space, is an informal and not well-defined term for radio frequencies lower than the AM broadcast band, which in Europe is known as "medium wave".

In the USA there have never been commercial longwave stations, though various WWV time signals are broadcast in that band.

reaperducer

8 hours ago

It was my father's morning alarm, too. But he was a couple of thousand miles away in New York state.

That, and Atlantic 252 (I believe now long gone) were what he woke up to every morning.

gavinward

7 hours ago

Despite the name I would not have guessed you could pick up Atlantic 252 in the US. The quality of it wasn't great for listening to music.

https://en.wikipedia.org/wiki/Atlantic_252

"Although the transmitter was in Ireland, the signal's reach meant that it was often looked upon as a "UK national station". Reception reports were received from such locations as Berlin, Finland, Ibiza and Moscow."

jmclnx

9 hours ago

That is too bad, you would think these could be kept active for historical purposes. But seems these services are all being turned off even though I heard a few were very useful in this day and age.

cjs_ac

7 hours ago

IIRC, their operation relies on enormous vacuum tubes that the BBC can’t get replacements for any more.

RachelF

7 hours ago

In some way it is short-sited, as radio is a good backup medium for global communications in case the entire Internet ever goes down.

Vacuum tubes also aren't vulnerable to nuclear weapon electro-magnetic pulses.

However, other than ham radio enthusiasts I guess no one listens to analogue radio anymore.

jasonjayr

5 hours ago

I got my RTL-SDR to see what I could listen to, and by the time I tuned in, nearly all the short wave stations I could tune to were just broadcasting evangelical religious stuff, or other crazy conspiracy stuff. It's remarkable that these powerful stations spend most of their broadcast day transmitting that content.

jstanley

3 hours ago

It's hard to believe that civilisation has lost the ability to build longwave radio transmitters.

gerdesj

6 hours ago

We do spend out quite a lot here in the UK for the BBC. They could easily dump a couple of expensive presenters and use the savings for vacuum tubes, if that is what is needed.

No idea where vacuum tubes were invented but I'm sure the BBC could find someone to make them.

downrightmike

5 hours ago

I wonder how many of the Van Allen radiation belts is held up by this