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VLF transmitter locations and power: obscured, or classified?

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This one edges up closer to the limit of what can be obtained through open or declassified government sources: a list of VLF transmitters, their locations, and power. Before anybody starts sending me links such as this one: http://www.thornett.net/Rosliston_Archive_2009-11/VLF_Transmitters_List.pdf, or this one, http://en.wikipedia.org/wiki/Very_low_frequency#List_of_VLF_transmissions, read on a bit.

I think there is good reason to believe that much of the publicly available information is inaccurate or obscured. This is not a conspiracy, but an expected hangover from the Cold War as well as the obvious need to classify certain types of military capabilities. For example, Deming (2004) discusses the possible role of the TACAMO (Take Charge and Move Out) airborne VLF transmitters in producing the Hum. The TACAMO system protects the continuity and integrity of communications in the command structure of US forces, in the case of any attacks against its land-based VLF transmitters. There is no need for the public to know where these planes are at any moment, but their broad areas of service are known. I think it makes sense in this case to be skeptical of the commonly quoted numbers for transmitting power.

We don’t have access to internal documents, and so I can only speculate that the actual number of big VLF transmitters – in particular their broadcast powers – could be considerably greater than commonly assumed.

Feel free to send to me whatever you have on this topic, as long as the references and documents appear in the public record.

 


13 Comments

  1. jimvandamme says:

    Just a comment on the TACAMO system. Some (20? 30?) years ago I got a VLF transmitter off an excess list with the intention of using it for building and testing inverter transformers for radar transmitters. Unfortunately I never got to use it because a field user begged me for the transistors, which were in short supply. Anyway, it wasn’t anywhere near capable of the 200 KW that’s quoted in places like Wikipedia. The trailing wire antenna, I’m sure had a very low radiation efficiency, nothing as “good” as the mile-wide nets used in ground stations. The bottom line is that a flying VLF transmitter/antenna would have a much lower output, compensated by possibly being much closer to the receiving sub. Maybe they had to come closer to the surface, too. The costs would be much higher to keep one running, also. So I don’t think there are large fleets of high-powered VLF transmitters circulating around. In peacetime, it is better to run the 1MW systems with big top hat antennas plugged into commercial power.

    • From what I can gather, there is no “peacetime” stance in anything related to nuclear infrastructure or critical military systems. 250 KW TACAMO power was the status 35-40 years ago. I think it would be silly to think that there have not been significant power gains since then.

      • wzrd1 says:

        The publicly acknowledged highest power VLF station in the world pushes out 1.8 megawatts. It is possible to transmit at higher power, but if it’s already effective at reaching submerged submarines at depth, it makes little sense to make the significant expense of transmitting substantially higher power.
        In regards to the hum, concerns over transmitter power of VLF stations makes little sense in the face of the inverse square law.

      • The inverse square law has nothing to do with this. VLF signals have minimal loss over thousands of kilometres. Please read the post regarding VLF propagation.

      • Wzrd1 says:

        The inverse square law has everything to do with it. Electromagnetic energy intensity is the inverse proportion to the square of the distance from the source. That works for light, gamma radiation, microwaves, UHF, VHF, HF, LF, VLF and even ELF. It works for sound as well. It’s a fundamental law of physics.
        What you are thinking of is absorbtion of the signal, which is minimal for VLF and ELF.

      • No, I’m afraid it doesn’t work that way with VLF propagation on Earth. You may be surprised to learn that the behaviour of VLF radio waves is strikingly different than, say, FM radio waves. If need be, I can refer you to standard sources from NASA, the Stanford VLF Group, and so on. Please go check what I am saying here. VLF propagates by three modes: line of sight, ground wave, and sky wave. The ground wave moves along the corridor between the ground and the bottom layer of the ionosphere, and the signal attenuation (loss) is minimal, on the order a few dB per 1000 km. In fact, a VLF signal will refocus at the antipodal point on the planet, creating a stronger signal there that places closer to the source! The skywave bounces between the ground and the ionosphere, often making multiple hops around the planet, again, with minimal signal loss. The inverse square law is an idealized model that is useful for describing signal intensity from point sources in which there are no obstructions, reflections, refocusing, and so on.

      • “How can waves focus on the far side of the earth?”

        Your microwave oven is a good example of standing waves. At 2450 MHz, you get only a couple of inches between maximums of a wave. It bounces off the metal oven walls and adds to the wave coming from the magnetron, and makes a series of hot spots. This will burn your food if not broken up, so you have to either rotate the food or have a “mode stirrer” in the oven to move the standing waves around.

        The same process happens acoustically. You will find places in a room where a bass note from a speaker will be louder, and places where it almost disappears due to cancellation.

        You can hear AM radio signals many miles away at night due to reflection off the ionosphere. At VLF frequencies, the waves travel unimpeded day and night. But depending on the frequency, different hot spots can form due to standing waves just like the microwave oven. They will change periodically with atmospheric conditions, and maximum points will move at an audio rate due to the frequency shift modulation of the transmit signal. If they transmitted a continuous wave, the power at one point would not shift much; but the modulation will produce a continuous buzz.

        Since there are multiple VLF transmitters, there will be multiple hot spots; also, they may produce beat notes between them. But due to the frequency differences, I would expect these beat notes to be higher in frequency than the bass notes that Hum hearers experience.

        Another effect is nonlinear intermodulation distortion, which is the result of diode rectification. This can happen in many structures such as corroded pipes and towers. The effect may be small, but it is there. I’ve had to carefully build receivers to mitigate this effect using filters and expensive amplifiers, because all active electronic devices are nonlinear to an extent.

      • Imagine if the surface of the Earth were nothing but smooth water, and a massive rock splashed into the ocean. Circular ripples would move outward, but imagine what would happen when that initial wave pulse moved toward the other side of the planet. The waves would start converging, and would indeed focus at the antipodal point. But of course water waves do not behave the same as VLF radio waves, and this is just an analogy. Incidentally, this has been established experimentally with VLF waves since the 1920s. Let me know if you’d like some references for that. As for the rest of what you wrote, it seems to agree with most of the science that I’ve read.

      • I’d guess that standing waves aren’t that much of a problem; nulls would be critical to receivers and the Navy doesn’t seem worried. The earth is kind of low Q, anyhow. If you lose 2 dB per 1K Km, your signal has 20,000 Km to reach its antipodal point, and it’s down to a fraction of its former strength. (I don’t want to do the exact math. I have a copy of WIPL-D somewhere but it hurts my head to run it.) So, in order to get the coverage, they had to build more transmitters widely spaced at west Australia, Hawaii, Seattle, Maine, etc.

        Anyways, how about an update on your shielding experiment?

      • Wzrd1 says:

        Inverse square law still is in effect. The energy spreads out. You’re speaking of constructive interference of reflected waves, which is another beast altogether. Going into standing waves, things get even hairer. Some have, however, touched upon Schumann resonance.
        But, communications at a standing wave point would be problematic.
        But then, the submarines are moving, the data rate is slow, so even a CRITIC or FLASH message is expected to take a fair amount of time to receive.
        Once such a message code is received, the submarine goes shallow and either uses radio or satellite to get a more complex encoded message.

        As I recall for US VLF transmitters, one is in Michigan, Wisconsin, Maine, Antarctica, Hawaii, England and I can’t recall one other that I’m aware of. Not counting non-NATO nations, which operate their own, with Russia having quite a few.

      • I’m sure Glen will point out to you the list of VLF stations; the SLF stations in the UP of Michigan and upper midwest have long been abandoned.

        As for your comment on radiometry etc.: you are in a microwave oven, except the box is spherical, has another sphere inside it, and you’re standing on the inner sphere. Also, the surfaces and air are lossy, and the air has a slight gradient of dielectric constant. One could calculate the incipient power level at any point on the inner sphere using an EM solver app, but it would be more accurate to just fire up a field strength meter at the points in question.

        I’d expect the nulls to be kilometers wide due to the wavelengths used.

        All this is peripheral to the question at hand: what causes the Hum? There are lots of other RF sources.

  2. jimvandamme says:

    Looks like they’re keeping the E4B’s running.

    http://www.militaryaerospace.com/articles/2014/10/boeing-e4b-subcom.html

    They claim 100KW transmit, which is logical considering the 1200KVA electrical circuit panel, and the loads of other stuff they have to power. Receiver improvements are cheaper than bigger transmitters.

    With only 4 built, running intermittently during crises, I think you need to point the blame somewhere else.

    • wzrd1 says:

      Those are alternative communications units, used to maintain command and control in case of major disaster or nuclear war.
      The primary stations are ground based, with the most powerful pushing out 1.8 megawatts.

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