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Electromagnetic frequency question

  1. Feb 2, 2010 #1
    Hey hey!
    I'm doing a project on detecting very low electromagnetic frequencies and was curious if anyone new the lowest frequency that we have the technology to detect. I was thinking of using that Yahoo answers for this question but I felt the general public wouldn't really know what I am looking for.

    What is the technology called?

    How much does it cost?
  2. jcsd
  3. Feb 2, 2010 #2
    Not totally sure on this but I think down in the area of 3 khz is the lowest electromagnetic frequency receivable.

    They used the ELF at one time to communicate with submarines. Not sure if they still do.

    Lots of natural ‘stuff’ in the low frequency band though, including lighting whistles, solar activity and Jovian storms.

    I built several VLF receivers years ago and they worked well. However, if I want to go into the low end of the band now I just tune in on my ham receiver. Actually, though it is not as good as the simple kits.

    There are still a few places around that deal in such things.

    The term is VLF DXing ( listen or searching out Very Low Frequency transmissions)

    You might be interested in these two sites.

    http://www.vlf.it/" [Broken]

    http://theinspireproject.org/index.php?page=order_vlf_receiver_kits" [Broken]
    Last edited by a moderator: May 4, 2017
  4. Feb 2, 2010 #3
    ELF (Extremely low frequency) band spans from 3 to 30 Hz. It was mainly used for communication with submarines.
    Anyway, when dealing with long wavelengths, one of the main issues is the size of antenna, which needs to be HUGE. Basically antenna size is proportional to wavelength, and for efficient transmission or reception it should be at least 1/10 of wavelength it is designed for. It is clearly not possible for, say, 3 Hz, because you would need 10000 km long antenna, so in some cases Earth itself is used as antenna.

    How much does it cost? Probably a lot, although I have heard for amateurs 'listening' to the earth's electromagnetic field, using long wires as antennas.
    Last edited: Feb 2, 2010
  5. Feb 2, 2010 #4
    Hi S.Vasojevic

    Antenna are much more critical in a transmit mode than receive in the lower end of the frequency spectrum.
    A good signal to noise ratio can be achieved with a simple (so called) long wire or a magnetic loop antenna.
    This is why low end commercial AM band radios will work with a short ferrite rod antenna or even a short piece of wire and easily receive a station at let’s say ≤650khz.

    On my General Coverage Receiver I only have a 20 ft dipole and use it for quite low frequencies. I could use a much shorter antenna yet.

    Even transmitting antenna can be made shorter than the wave length by using multiples of the frequency, base loading and electronic antenna tuning.

  6. Feb 2, 2010 #5
    Thanks Ron. You are right. But since the OP posted in Astronomy forum, I was under impression that he is keen to listen to 'out of earth' signals, and possibly lower than 3 Hz. I am out of my zone here, but I would assume that you need big antenna for that, or not?
  7. Feb 2, 2010 #6
    I was under the same impression. I thought perhaps he was interested in solar ‘noise’ or solar flares. Both of which ‘splatter’ over the radio spectrum into the VLF range and relatively easy to receive on simple VLF receivers.

    It would certainly be advantageous to have a very long antenna but not totally necessary.
    Or perhaps I better rephrase; not that necessary for simple receivers operating at that level.

    Just about any type wire antenna, especially something with multi strand individual insulated wires to increase the effective surface area.

    Actually, I have received http://en.wikipedia.org/wiki/Dawn_chorus_%28electromagnetic%29" [Broken] with a simple whip antenna years ago when playing with Low Frequency stuff.
    Last edited by a moderator: May 4, 2017
  8. Feb 3, 2010 #7
    Thanks guys the information you gave was excellent. no more help needed.
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