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Old 21st May 2022, 12:28 am   #21
fetteler
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Default Re: BIG transmitter

When did the 16kHz VLF transmitter at Rugby stop operating? I don't recall seeing the masts from the M1 for some time now.

Steve.
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Old 21st May 2022, 1:02 am   #22
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Default Re: BIG transmitter

Hello,
According to this https://en.wikipedia.org/wiki/Alexanderson_alternator, VLF altrenators were used by the US military in the second world war and beyond.
Yours, Richard
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Old 21st May 2022, 2:51 pm   #23
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Impressive stuff! The nearest I've got to this experience was starting up the 3 phase generator for a large marine radar transmitter. I have no idea how the generator worked but it was a huge noisy thing in a large room. The scariest bit was when the generator did its power on self test routine. It generated a 3 phase 300A supply and when it tested itself under load the dials briefly went to 300A full scale. It felt like the whole room shook when it did this and it did it two or three times in quick succession.
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Old 22nd May 2022, 1:06 am   #24
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Default Re: BIG transmitter

Having been not exactly inundated with replies I did some reading and answered my own question. Apparently eight of the twelve 'tall' masts at Rugby (so iconically visible from the motorway) were obsolete and demolished on the night of 19 June 2004 to 20 June 2004 with the remaining four masts suffering the same fate on 2 August 2007.

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Old 22nd May 2022, 2:22 am   #25
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Default Re: BIG transmitter

Interesting. It's presumably an important comms facility for American subs in the Indian Ocean and western Pacific, as well as the RAN.

I think you are correct Paul. Our submarines are all in dry dock as they make so much noise they can be heard 200 miles away, BY EAR, when they are submerged. You are all aware of the $5 billion gift to the French government for nothing.

Joe
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Old 22nd May 2022, 7:07 am   #26
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Default Re: BIG transmitter

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Originally Posted by paulsherwin View Post
You don't need VLF for surface ships, which can just use satellite military comms, with HF as a backup.
There also isn't much bandwidth available on VLF due to simple arithmetic, so that part of the spectrum can't handle a fraction of the traffic of satellites or HF.

There is a communications channel, but it's a very thin one, so it's best reserved for the uses which need its special properties.

Messages to subs must be rather terse and with no back channel for sending confirmation, I assume a number of repeats are sent. It would also make sense to run up the VLF transmitters on a regular schedule and send undecipherable junk messages in lieu of real traffic so that an opponent can't deduce something is about to happen by looking at the amount of traffic. This could also serve to confuse cryptanalysts.

David
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Old 22nd May 2022, 4:29 pm   #27
Graham G3ZVT
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Default Re: BIG transmitter

Given the limited channels availible, and the sensitive uses governments put their allocations to, I am surprised that a group of amateur enthusiasts are allowed to run the Grimeton transmitter, even on special occasions.

Long may it continue!
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Old 23rd May 2022, 1:35 pm   #28
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Default Re: BIG transmitter

Rugby VLF having closed-dowm it's worth noting that its counterpart at Criggion, near Welshpool, also went QRT in the early-2000s.

http://www.oswestry-history.co.uk/cr...o-station.html
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Old 23rd May 2022, 7:08 pm   #29
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Default Re: BIG transmitter

Quote:
Originally Posted by Hartley118 View Post
Quote:
Originally Posted by Roger Ramjet View Post

2. Would anyone living close by have been able to extract "power", from the antenna using a suitable resonant coil (albeit only when the morse key is pressed) ?

Rog
My father, born and brought up not far from Droitwich, told me that when the high power 200kHz BBC transmitter there was commissioned, local residents complained that they couldn’t turn off their bedroom lights completely. They continued to glow because the wiring was picking up the 200kHz carrier and extracting power from the transmitter. It was though deemed a nuisance rather than a useful source of power.

Martin
I once heard a story about the same transmitter. Don't know how true it was. Someone close by put some kind of an antenna in their loft, with a rectifier, and fed some lights in the house. It led to a significant drop in signal in the area 'shadowed' by the thief and hence they were found out and prosecuted.

As I say, something I heard, no proof.

Still have family in the area. Actually handed a car over to my SiL in the car park of Webbs in the shadow of those masts.
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Old 23rd May 2022, 7:39 pm   #30
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Default Re: BIG transmitter

There are certainly plenty of urban myths about people living close to big transmitters, but it seems extremely unlikely that enough energy could be harvested to light a house, and I can't see how the transmitter operators would have noticed it anyway. There are more plausible stories of people being able to hear Droitwich on their gas cookers, and it should certainly be possible to light a small neon lamp.

Don't forget that Droitwich (and indeed Grimeton) were baby stuff where LF transmission was concerned. There were quite a few LW broadcast transmitters in Europe and Russia running over 1MW, and the Americans were shoving 10MW into the Cobra Mist array at Orfordness in an attempt to get OTH radar to work. The USSR 'Russian woodpecker ' radar needed so much power that they built a complete nuclear power station complex (Chernobyl) primarily to service it.
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Old 23rd May 2022, 9:18 pm   #31
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Default Re: BIG transmitter

As a local of Brookmans Park there are plenty of these stories in the local folk lore.
People hearing Radio 4 on their new dental fillings, it coming out of cranes, somebody lit up their house with a coil in the loft and they found it by a hole in the radiation pattern +blah.

"All I know is" I could just light a grain'o'wheat bulb off my crystal set when it was tuned up right on 909kHz (the big one). LEDs came later - easy peasy.

And I could listen to The Archers with a crystal earpiece and a 33k resistor clipped to the school classroom radiator. The background spitch was Radio 1, BBC R.London and whatever else they were sending at the time.

Last edited by Jon_G4MDC; 23rd May 2022 at 9:25 pm.
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Old 25th May 2022, 1:46 am   #32
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Default Re: BIG transmitter

The Oz Omega station in Victoria was VLF....

From Wiki...

Station G, near Woodside, Victoria. Ceased Omega transmissions in 1997, became a submarine communications tower, and was demolished in 2015.

Omega was approved for development in 1968 with eight transmitters and the ability to achieve a 4-mile (6.4 km) accuracy when fixing a position. Each Omega station transmitted a sequence of three very low frequency (VLF) signals (10.2 kHz, 13.6 kHz, 11.333... kHz in that order) plus a fourth frequency which was unique to each of the eight stations.
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