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Old 18th May 2022, 11:03 pm   #1
joebog1
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Default BIG transmitter

I was surfing yesterday when I found this.

https://www.youtube.com/watch?v=f6cEm9A71g8

A 200 Kw no valves transmitter made in 1920 something. Some of you will know about it, for those that havent its a superb piece of history. Note the quality of the equipment itself!!.

AND for those that like longwaves its output is at 17 Khz plus a bit. Apparently you cant use a tweeter as a receiver.


Joe
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Old 18th May 2022, 11:09 pm   #2
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Default Re: BIG transmitter

IIRC this transmitter is actually used once a year, and somewhere on this forum there is a report about this.
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Old 18th May 2022, 11:15 pm   #3
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Default Re: BIG transmitter

The Grimeton transmitter is well known here Joe. They fire it up periodically, and the signal can be received easily in Britain with the right equipment. It probably struggles to reach QLD though.

Wiki article: https://en.wikipedia.org/wiki/Grimeton_Radio_Station
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Old 18th May 2022, 11:31 pm   #4
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The vid I posted is actually "firing it up ". And fire it up they do!!. The only thing missing is a bloke called Igor to pull those massive ( slightly burned ) knife switches. All the exposed slip rings, brushes and commutators. You definately need a certificate of proficiency in that transmitter hut!!!.

I was struck by the accuracy of a purely mechanical "governer ", to keep frequency accuracy. Yes I know its not PLL, but the inertia in all that rotating heavy equipment would help I guess, but one needs the get it "to speed " first, THEN maintain it there.

In any case, I was highly impressed.

Joe
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Old 19th May 2022, 12:22 am   #5
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Default Re: BIG transmitter

Nice to see that the operator was using a Swedish style key. I find them very comfortable to use with their leaf-sprung contact, and very precise, but they do tend to make your speed run away with you.

Youtube doesn't do the film any favours with the relay movements, the meter jumps and the flashing bulb all out of sync with the sidetone.

Great film, though.

David
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Old 19th May 2022, 9:15 am   #6
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Default Re: BIG transmitter

Quote:
Originally Posted by joebog1 View Post
The vid I posted is actually "firing it up ". And fire it up they do!!. The only thing missing is a bloke called Igor to pull those massive ( slightly burned ) knife switches. All the exposed slip rings, brushes and commutators. You definately need a certificate of proficiency in that transmitter hut!!!.

I was struck by the accuracy of a purely mechanical "governer ", to keep frequency accuracy. Yes I know its not PLL, but the inertia in all that rotating heavy equipment would help I guess, but one needs the get it "to speed " first, THEN maintain it there.

In any case, I was highly impressed.

Joe
I've noticed that when they are trimming the aerial tuning/matching, there is often a small change in frequency, maybe 10 or 20 Hz due to the loading on the alternator.
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Old 19th May 2022, 10:40 am   #7
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Default Re: BIG transmitter

In the Youtube comments, there's some info on frequency control. As I understand it, when it's keyed 'on' and the load increases, the speed would tend to drop... but it's compensated by a separate set of of relay coils altering the impedance (wound rotor?) in the induction motor which drives it, so the driving torque is increased.

I guess in theory this is capable of under- or over-compensation, thus it should be possible to maintain frequency exactly, once set up.

Presumably, an induction motor is used rather than a synchronous, because the output frequency is needed to be more accurate than the AC utility frequency, and an induction motor with its slight 'slip' can achieve this with suitable control?
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Old 19th May 2022, 3:34 pm   #8
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Default Re: BIG transmitter

Thanks Joe, you have started a really interesting thread. I never knew an alternator could double up as a Radio Transmitter & wonder if any other versions are out there ?

I have only basic knowledge of Radio theory so wonder if someone could answer the following please:-

1.Would the antenna wires be "end fed" from one connection to the alternator with a separate earth connected to the other connection ?

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
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Old 19th May 2022, 5:30 pm   #9
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1) Yes/No/Maybe/Depends. Usually low frequency antennae are a vertical with a huge 'capacity hat' on top. The bottom is driven against a huge earth mat. some form of matcher/tuner can be expected where the feeder meets the vertical and the mat.

2) Yes, a little. But that's also true of higher frequency transmitters,, and it's easier to have an efficient receiving antenna. This is how crystal sets work.

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Old 19th May 2022, 5:53 pm   #10
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Default Re: BIG transmitter

There were a lot of alternator transmitters built in the 1920s for long distance communications where an undersea cable wasn't available or practical. They were mostly replaced by electronic HF transmitters in the 30s, and Grimeton is now the only survivor.
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Old 19th May 2022, 9:25 pm   #11
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Default Re: BIG transmitter

Quote:
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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.

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Old 19th May 2022, 11:25 pm   #12
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Reason I posted that link, is that in my time and all the schools I have been through, (school, college, university and some specialised stuff ) NOBODY ever mentioned low frequency transmitters. Especially "mechanical " ones.

Roger I think has had the same "non-education ".

Joe
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Old 20th May 2022, 6:16 am   #13
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Default Re: BIG transmitter

Quote:
Originally Posted by paulsherwin View Post
The Grimeton transmitter is well known here Joe. They fire it up periodically, and the signal can be received easily in Britain with the right equipment. It probably struggles to reach QLD though.

Wiki article: https://en.wikipedia.org/wiki/Grimeton_Radio_Station
It’s regularly heard in Alaska by an old mate of mine!
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Old 20th May 2022, 6:30 am   #14
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Default Re: BIG transmitter

There have been several high power low frequency transmitters built much more recently. Nuclear missile submarines go and hide where potential enemies can't find them. Communicating with them without giving away clues to where they are is difficult. Very low frequency radio has the advantage of a deep skin depth in salt water oceans and can be received in a submerged vessel. It also has the advantage of global coverage if powerful enough.

Look up Jim Creek Radio Transmitter:

https://en.wikipedia.org/wiki/Jim_Cr..._Radio_Station

to see one.

The Americans also planned a VLF transmitter using electrodes in the sea on opposite sides of a dog-bone shaped island. Using the conductivity of the sea water as a loop antenna. I'm not sure if they built it.

VLF comms was a technology of prime importance in the cold war. The receivers used tiny bandwidths and correlation techniques to find and read the very weak signals. Consequently, the data rate was extremely low.

https://en.wikipedia.org/wiki/Skelto...itting_Station

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Old 20th May 2022, 10:44 am   #15
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Default Re: BIG transmitter

Quote:
Originally Posted by joebog1 View Post
Reason I posted that link, is that in my time and all the schools I have been through, (school, college, university and some specialised stuff ) NOBODY ever mentioned low frequency transmitters. Especially "mechanical " ones.
Alternator transmitters were a relatively short lived technology and all the ones I'm aware of were used for transatlantic comms. I don't think any were built in Australia. Grimeton survived so long because Sweden lost access to the transatlantic cable system during WW2, and postwar it was used as a VLF transmitter for the Swedish navy. It was only decommissioned in the early 60s and continued to be maintained in reserve even after that.

There may be an (electronic) VLF transmitter in Aus somewhere for the RAN, but it's possible they rely on the Americans or Brits for comms given the size and makeup of the submarine fleet.
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Old 20th May 2022, 4:33 pm   #16
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Default Re: BIG transmitter

I expect that "non-ferrous content" was what assured the rapid elimination of the alternator transmitter once they became outmoded. As Paul says Grimeton was lucky to have a continued role because of circumstance and by time it was finally out of service it was appreciated as a historical artefact. It's a, um, classic tale with classic things that there's an interval between "obsolete old rubbish, bin it" status and "lovely heritage item, preserve it" status, during which the majority are doomed to disappear for good.
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Old 20th May 2022, 10:19 pm   #17
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We do have one Paul, North western Australia somewhere. It is for navel use, but I dont know where it came from. I believe its for our non submarines.
I discovered this while looking for more on low frequency transmitters.
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Old 20th May 2022, 11:19 pm   #18
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You don't need VLF for surface ships, which can just use satellite military comms, with HF as a backup. Subs use VLF as it will penetrate water to some extent. VLF is more important for nations with fleets of nuclear powered subs, which may stay submerged for weeks or even months at times of international crisis. Aus doesn't operate nuclear subs at present, but there has recently been the controversial AUKUS deal to procure some (these would be attack subs, not nuclear weapon launch platforms.)

https://en.wikipedia.org/wiki/Aukus
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Old 20th May 2022, 11:24 pm   #19
joebog1
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I am very aware of that Paul. My TV set is permanently tuned to the ABC ( equivelent to BBC ) news service.

https://en.wikipedia.org/wiki/Naval_...Harold_E._Holt

I am somewhat of a nerd with the subject that cant be discussed here .

Regards
Joe
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Old 20th May 2022, 11:33 pm   #20
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Interesting. It's presumably an important comms facility for American subs in the Indian Ocean and western Pacific, as well as the RAN.
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