Talk:Extremely low frequency
|WikiProject Physics||(Rated Start-class, Low-importance)|
The frequency range quoted (3-30 Hz) seems to be in error. According to the IARC Monograph on Static and Extremely Low-Frequency (ELF) Electric and Magnetic Fields, the "extremely low-frequency (ELF) range [is from] (3–3000 Hz)." ralian 03:28, 24 October 2007 (UTC)
You are correct. 30-3000 Hz should be the correct frequency listed. Military classifies this frequency range as ELF. Plus, converting 3-30 Hz into wavelength only gives you a tiny portion of the ELF range. —Preceding unsigned comment added by 18.104.22.168 (talk) 03:29, 8 April 2008 (UTC)
"Despite the extremely high electrical conductivity of salt water, the water's density shields submarines from most electromagnetic communications."
Don't conductors stop EM waves? - Omegatron 14:58, Aug 16, 2004 (UTC)
It's not quite that simple, but yes, I think the high conductivity of water serves to reduce the wave transmission. I'd need to do the maths, though, before I feel secure in changing the article. Kaet
Just was about to ask the same as Omegatron. So, Kaet, did you do the maths? Simon A. 13:21, 7 Sep 2004 (UTC)
I asked this question of the chairman of the Physics Department back at my college in the mid 80's. Short answer is that conductivity is a function of frequency, not an absolute quantity. User:David Battle
Generally, the higher the conductivity of a substance, the less electromagnetic radiation will pass through it. From my copy of Griffiths' "Introduction to Electrodynamics" (p. 394), the skin depth (the characteristic depth to which an EM wave penetrates) is
(my apologies, I don't know how to format math here yet). In the limit of high conductivity and low frequency this simplifies to , where sigma is conductivity. You can find this formula also in Jackson's "Classical Electrodynamics" (p. 220). So, when conductivty becomes large (compared to some "characteristic conductivity" that depends on frequency), EM waves don't penetrate far. As a sanity check, empty space is completely non-conductive and transmits EM waves perfectly, while a conducting Faraday cage is used to shield from radiation. I hope that helps. -- Unperson, of everything2 fame
I haven't been able to find anything to substantiate the line that says the Wisconsin and Michigan facilities were dismantled in 9/2004. Did this actually happen? jdb ❋ 08:46, 20 Jan 2005 (UTC)
- This is dated 9/2004 - "Navy Set to Ditch Its ELF Systems"
harm to humans.
Can ELF waves/arrays cause harm to living creatures? - Zepheus 19:57, 31 May 2006 (UTC)
http://www.raven1.net/elf.htm <-this maybe of interest
effects on the brain
Can ELF waves effect brainwaves?
- From reading the information the author of that article gave, which is the same experiment in the link above, incidentally, there is a big problem with the experimental setup.
The author, Walonick, sated the following: "The transducer was a 24" diameter hand-wound coil, consisting of 1000' of #25 magnetic wire. The coil had a DC resistance of 32.4 ohms. It was mounted on a 26" square piece of bakalite board for stability."
This describes the antenna. Further down the article:
"The voltage fed to the coil was 3.1 VAC (RMS). The coil was positioned 18" in front of the subjects head. The outputs from the ELF transmitter (function generator) and the brain wave monitor were fed directly into the computer A to D board, allowing both to be displayed on the computer monitor (and recorded on disk) simultaneously."
There are several fundamental issues with this experiment, the first being that unless it was a Placebo/double blind trial, it was non-functional.
The coil described would have an inductance of about 5mH, which would have a resonant frequency of 2kHz. As this is being used as an antenna, I've computed a -69dB Gain. The input is 3.1VAC RMS, with a source impedance of 600 Ohms for the signal generator given. The impedance mismatch of 30:1 will cause even worse signal out of the antenna, essentially none. The Radiated power from the coil would be in the picowatts, with more signal radiating from the connection leads.
The measurements by the EEG changing were most likely due to capacitive coupling of the cables leading between the EEG and the coil, and not anything from the brain itself.
ELF Transmissions require a tremendous amount of power, and ridiculously long antennas to propagate. A loop antenna isn't of much use below 500kHz, let alone 5-15 Hz.
In other words, from an engineer: The information in the link given is incorrect due to interference, with a dose of the experimenter finding what he wanted to find, rather than any actual change in the minds of the very small sample of volunteers. 21:26, 10 July 2010 (UTC) —Preceding unsigned comment added by 8r455 (talk • contribs)
Serial Experiments Lain? I haven't seen enough of the show to know if this is utter fanboy crap, putting this link here. But it smells strongly of it. Is it actually discussed in enough detail to warrant inclusion here?
Basically, all the other "see other" links are to radio-related topics. If someone wants to create a new section for references in fiction, fine, put it together with Tom Clancy. Until then, screw it I'm deleting it. User:Andy_Christ
I think there should be a section on the impact of elf waves on humans. Thats what i was looking for and instead you suggest I look up Tom Clancy??? Well okay duh. Why didn't i think of that? —Preceding unsigned comment added by 22.214.171.124 (talk) 05:21, 27 June 2008 (UTC)
There have been some concerns over the possible ecological impact of ELF signals. In 1984 a federal judge... (judge from what country?) 126.96.36.199 21:01, 5 January 2007 (UTC) [DubSnipe]
Can somone verify this?
- Sounds reasonable to me. It's not talking about pigs, its talking about Pipeline inspection gauges (Pig) and Pigging. "Communications are achieved by an extremely low frequency electromagnetic system that performs efficiently in both steel and seawater media. During pigging operations the plug emits a beacon that permits tracking. The accuracy of plug positioning is within +/- 100mm."Subsea Pipeline Solution Pipeline & Gas Journal, August, 2000. Try googling pipeline pig extremely low frequency for more items. --Dual Freq (talk) 14:26, 4 July 2008 (UTC)
What about other ELFs
- See Super low frequency for 30-300 Hz. Sometimes the technical use of therms like ELF, UHF etc does not follow closely the 3/30/300 classification. Sv1xv (talk) 16:39, 20 April 2009 (UTC)
- What is the 3/30/300 classification? Electromagnetic therapy often uses the term ELF to describe Extremely low frequency. Some articles on electromagnetic radiation and health also utilize the term. --CyclePat (talk) 22:39, 20 April 2009 (UTC)
- Is it 3 to 30 ELF, 30 to 300 SLF? Hence 3/30/300? --CyclePat (talk) 22:40, 20 April 2009 (UTC)
- By 3/30/300 I mean exactly that: LF: 30-300 kHz, MF: 300-3000 kHz, HF: 3-30 MHz, VHF: 30-300 MHz, UHF: 300 MHz - 3 GHz etc. See also Template:Radio spectrum. Sv1xv (talk) 04:10, 21 April 2009 (UTC)
ELF vs SLF vs ULF confusion
As a first time reader, this article is confusing. If ELF range is 3-30Hz then why does the article talk about military applications which are actually in the SLF range? If the 'military speak' doesn't line up with the scientific classification this should be made explicit.
Also the article needs to better explain how we can broadcast in this range if the antenna (in theory) needs to be thousands of kms long... ! It doesn't make this clear at the moment. There must either be a solution (workaround), or the military actually uses higher frequencies, e.g. SLF or ULF? Amilnerwhite (talk) 23:40, 10 November 2009 (UTC)
reference found for 3 30
found a reference for the 3/30 http://lws-trt.gsfc.nasa.gov/trt_liemohn05eos.pdf and this one categorizes all the bands. http://er.jsc.nasa.gov/SEH/f.html --CyclePat (talk) 07:16, 7 February 2010 (UTC)
I have reverted CyclePat's recent changes as fail to meet our criteria on several points. Per WP:UNDUE, the additions and new sections give undue prominence to single primary sources or WP:FRINGE sources, and some of the content is itself WP:FRINGE - hence fails our NPOV requirement. Further, they are not all WP:RS, and WP:MEDRS for medical claims, and therefore not suitable. This article should not be used as a WP:COATRACK or for WP:ADVOCACY, and must stick to WP:NPOV. If you feel some of these edits have merit please justify here, with RS as appropriate. Discussion is better than editwarring. Thanks, Verbal chat 13:03, 12 February 2010 (UTC)
- The new section is also a clear violation of WP:SYNTH, as well as not being very clear. CyclePat, please self revert and discuss these edits and additions, otherwise the article will have to be tagged as POV and OR. Verbal chat 13:07, 12 February 2010 (UTC)
- I'll be happy to give you a phone call to discuss this. We can record the conversation and publish it here on the talk page. In the meantime,
- 1) Since when does the addition of "new sections" give undu prominence to single primary sources? And why? If you explained the principle and an example, perhaps we could be on our way to a better start. In fact, per WP:UNDUE, I could argue that what I'm doing is correct. That's because "Neutrality requires that the article should fairly represent all significant viewpoints that have been published by a reliable source, and should do so in proportion to the prominence of each). However, please explain, why you believe this. The majority viewpoint, in our case the 3 to 30 hz, is simply not well referenced. If I could find more "peer-reviewed" information about that, then I would be putting it in. (Is this what you are alluding too?)
- 2)HAHAHAHAHA! LOL! Fringe sources... Yeah... the World Health Organization. And NASA... and the Government of Canada.... LOL... I think you may have watched to many X-files TV series. (b.t.w.: isn't there a popular episode about how the military tested ELF and this guy had to keep driving West because it influence his body functions?)
- 3)This is not a coat rack. I'm simply describing what well sourced, peer-reviewed journals say, as well as government agencies, regarding ELF. (I will say this one, ELF is simply a frequency.) The WP:UNDUE POV, which I've quickly analyzed, may be the military communications. ELF is used in many fields (pun intended), and hence, military communications is simply one branch of ELF. If you are concerned about this article becoming a medical article, as, in past, you have display dissent towards articles that utilize medical "peer-reviewed" journal, please WP:AGF and note that these are relevant, and pretty much the "majority" or easily accessible information regarding ELF. If you have some more information and references, please do add them. Thank you. And, you may refer to me in the first person... Thank you Verbal.
- 4) Wow! A violation of synth? NO, I don't think so. So please, do elaborate!! If the description of ELF is "unclear", it is simply because the facts (or opinions) of what quantifies as the frequencies of ELF are, in of itself, unclear between scientist. Ideally, we would find a source that says this.
- --CyclePat (talk) 13:44, 12 February 2010 (UTC)
- I do not see an issue with the additional content CyclePat has added. The primary use of the ELF band has been for communicating with submarines, using VERY short messages. The exact details of the communication methods, by the US in particular, are NOT for public/global exposure for obvious reasons, which leads to a lack of sources. This leaves legacy information/experiments as the only sources. Nearly all "Health Aspects" of low frequency EM waves in the US have been carried out in the 50-60Hz Range, which is in the SLF range, conducted on families near power lines, etc. These are above the "Traditional" ELF Band. I am new here somewhat, so forgive my misunderstandings. I feel most of the content with related flags should be in the SLF section. I would suggest the generation of a "Wiki Standard EM spectrum chart", and decide on a solid range of what constitutes Extremely Low Frequency. The ITU bands and the US Bands are quite close. The Planck-Einstein equation shows that ELF transmissions have low energy, compared to FM radio, which we are bombarded with in much heavier doses. Any study of higher frequencies and health would be irrelevant unless applied directly to the ELF spectrum. 8r455 (talk) 20:46, 10 July 2010 (UTC)
Antennas are used to amplify voltage (amplitude) by means of electrical resonance through induction. Any moving electric field will result in a corresponding magnetic field which emanates into free space indefinitely. An antenna is only required if the threshold of the detection equipment is below the amplitude of the transmitted wave.
As antennas function on the principle of resonance, for a properly tuned antenna, its size needs to be related to the wavelength. If not, electrical resonance won't occur and the signal will not be amplified.
Dubiousness of installing ELF antennas on submarines
Why is this statement marked as dubious? It seems obvious that it would have been impractical, otherwise they would have done it. — Preceding unsigned comment added by 188.8.131.52 (talk) 23:45, 23 January 2012 (UTC)