Talk:Ultra low frequency

I'm interested to know why there are no man-made transmitters in this range. I know next to nothing about radio matters in general, but I assume there is limited bandwidth at this range which makes transmission a waste of time. But if that's true, why are there transmissions on SLF and ELF? — Trilobite (Talk) 03:01, 24 Nov 2004 (UTC)

Mainly because you'd need an extremely long and the resulting signal would have almost no energy. Another limitation is that it is a very slow way (in information per time) method of sending messages. The even lower frequency ELF (extremely low frequency) is used to communicate with submarines because it can penetrate sea water to an appreciable depth (which is difficult). I changed the article to say no communications transmitters. There are signals in that range but it is just noise released by slowly changing electrical signals. RJFJR 16:48, Apr 2, 2005 (UTC)

ULF is used to detonate explosives in mines. You don't need to lay wires which just get blown up anyways. Pogostix 02:08, 31 Jul 2005

There are transceivers in use in this range. I work on directional drilling gear in the oil & gas industry, and we have some downhole RTs that operate in the ULF range. This is because they only need to transmit a short distance (tool to tool, not tool to surface), and higher frequencies would be quickly absorbed by the surrounding rock formation. Our RTs are operating at around 2kHz. I also wanted to add that there are no references listed in the "Earth Mode Communications" section. As a radio enthusiast and all-around geek, I found that section really interesting, and I would love to see some sources cited. Beefington (talk) 12:54, 22 October 2012 (UTC)

I think that there is an error in the frequency described to take up this ULF band. Please change this article accordingly!

Hyphen

I have undone the move to a hyphenated name. This is against the normal convention. Although ultra low frequency is a rare term in radio engineering one can compare ultra high frequency which is never hyphenated in the literature. SpinningSpark 01:06, 20 December 2013 (UTC)

It looks better without the hyphen. Graeme Bartlett (talk) 11:06, 20 December 2013 (UTC)

Should this be a disambiguation page?

The first sentence of the lede suggests that this article is about ULF (ITU), i.e, 300 hertz and 3 kilohertz. However, most of the article seems to be about ULF (electromagnetic waves) as used in science, e.g. geology, geophysics, studies of the ionosphere and magnetosphere, and astronomy. There is of course the additional problem that ULF can also refer to acoustic and gravitational waves. The point is, Wikipedia is not a dictionary. Articles should focus on concepts, not words and their multifarious meanings. At the very least, we should drop the ITU definition of ULF from this article and replace it with a hatnote pointing to [[1]]. I think this article should focus on ULF (electromagnetic waves) as understood by the scientific community rather than the radio engineering community. If radio engineers need an entire article about ULF (ITU) they can write one. Zyxwv99 (talk) 16:34, 13 July 2014 (UTC)

I can't really agree with that, the article is about radio engineering, the fact that the term is also used in acoustics and gravitational waves is irrelevant. If they want an article, they can write one. Is there any evidence that scientists studying the magnetosphere etc use a definition different from the ITU? Even if they do, I don't think that justifies a split of the article just on those grounds, we are still talking about fundamentally the same physical phenomenon. The title of this article follows a pattern that includes the more well known terms very high frequency and ultra high frequency. Those should certainly have the main title as they are well known to the public (or at least their acronyms are) and it would be a shame not to keep the whole series consistent. I would only support such a change if it could be shown that something else had incontrovertible claim to WP:PRIMARYTOPIC. SpinningSpark 18:33, 13 July 2014 (UTC)

Apparently you have misread my comments. Please read them again. This discussion is not about acoustic or gravitational waves; I merely mentioned them as an aside. The fact that you would direct your response at an aside, misrepresenting it as the subject of the discussion, is profoundly disturbing.

The main point was that this article, as it stands now, is almost entirely about ULF waves (electromagnetic) as the scientific community generally uses the term, as opposed to how the term might be used in radio engineering. If you don't believe me, try reading the article and see what the references are talking about. The vast majority are talking about something completely different from ITU ULF.

Try doing a Google search on ultra-low-frequency electromagnetic radiation, or any variant thereof. Aside from conspiracy-theory websites (not relevant) most of what comes up relates to geophysics, the magnetosphere, the ionosphere, and astronomy. They are talking about microHertz, milliHertz, and single-digit Hertz radiation (although they tend to speak of 1000-second periods rather than using the term "milliHertz").

If you think this article should be about ULF (ITU) then please make it so. At present the first sentence of the lede is deceptive. Zyxwv99 (talk) 20:17, 13 July 2014 (UTC)

The first sentence of the lede gives the ITU definition. The second sentence gives three alternative deinitions so I don't see how this is falsely pretending to be exclusively about ULF (ITU). Your point about the content of the article: setting aside the lede which is supposed to be a summary (but probably fails in this) about one third of the article is about earthquakes and two thirds are about Earth mode communications. The latter is surely radio engineering no? In any case, we can only have a disambiguation page if there are other articles to disambiguate. Do you have other articles to point to which could go on an ultra low frequency disambiguation page? SpinningSpark 22:38, 13 July 2014 (UTC)

You're right, earth-mode communications is an application of VLF and ULF (ITU definition). The section on earthquakes really belongs in Magnetohydrodynamics#Applications, since these are actually ultra-low-frequency MHD waves. Even though MHD waves are "electromagnetic" and a type of wave or radiation, they do not propagate at the speed of light are not really a type of EM. Zyxwv99 (talk) 23:45, 13 July 2014 (UTC)

In what sense are they not EM? DEMETER is orbiting in space so is only going to be able to detect stuff propagated to it as EM waves. I'm not sure why the propagation speed is relevant here, presumably this is not the speed of light because the wave is travelling through a medium while in the Earth, but in any case, whatever the source of the radiation, it is an EM wave reaching DEMETER, it reaches it at the speed of light, and its detection is within the ambit of radio engineering. SpinningSpark 00:08, 14 July 2014 (UTC)

Demeter is measuring EM. However, other satellites measure MHD from seismic activity. It gets into the ionosphere through MHD beams coming up from the ground. The people in charge of Demeter define ULF as follows: DC / DC / ULF [0-15 Hz], ELF [15 Hz-1 kHz], VLF [15 Hz-17.4 kHz] and HF [10 kHz-3.175 MHz]. [2] Meanwhile, the article about Loma Prieta makes it clear that EM was not measured, but magnetic oscillations "in the ULF range (0.01-10 Hz)". These phenomena are linked, since MHD and EM can induce one another (both ultimately due to piezoelectric and piezomagnetic effects). I guess we'll have to think about this some more. Zyxwv99 (talk) 03:35, 14 July 2014 (UTC)

"...MHD and EM can induce one another..." It is not only "can", there is a definite "will". A changing magnetic field implies an electric field. This is a fundamental consequence of Maxwell's equations:

$\nabla \times \mathbf {E} =\ -{\frac {\partial \mathbf {B} }{\partial t}}$

A changing magnetic field and a changing electric field together imply an EM wave. It is an inevitable result of fundamental principles. SpinningSpark 08:25, 14 July 2014 (UTC)