# Low frequency electromagnetic waves

Some frequencies of electromagnetic waves are used for transmission of information, like radiowaves, microwaves, light, but some are not..

Perhaps low frequencies aren't used for transmission simply because the waves haven't got enough energy to reach the destination, but it's well-known that if you go near a high voltage transmission tower, you can turn on a fluorescent lamp http://www.electric-fields.bris.ac.uk/

Perhaps the intensity of the high voltage gives more photons to interact there, than in a home installation, but the fact is waves are traveling anyway at 50/60 Hz without need any modulation.

There is a limit on how low a frequency can be to put photons into travel?

Very Low Frequency (VLF) and Extremely Low Frequency (ELF) radio waves are used for communication between submarines, because higher-frequency radiation doesn't propagate well through sea water.

I think the main reason they're not used much outside of the water is simply that higher frequencies are easier to use for a number of reasons. For one thing, the lower the frequency you're trying to use, the longer your antenna needs to be. For another thing, the rate at which you can send information depends on the bandwidth (i.e., the range of frequencies you're using). There just isn't much bandwidth at the low-frequency end.

• hi!, thanks. Do you think it's possible to make a double slit experiment for low frequency with bigger slits? has it been done?
– HDE
Commented Mar 6, 2011 at 17:08
• How big? It's easy to do it at centimeter wavelengths -- that's a common student lab experiment. It'd be hard to do it with kilometer wavelengths, and not worth the bother. Commented Mar 6, 2011 at 17:37
• I've read in wikipedia this statement : "the energy carried from one winding of a transformer to another, in quantum terms, is carried by virtual photons, not real photons" it's a strange statement, I don't know what is the limit for that, what are the frequencies for virtual or real photon interactions..
– HDE
Commented May 13, 2011 at 11:44

To complete Ted Bunn's answer in most telecommunications applications the informations are transmitted by the far field which is present from about two wavelengths from the source to the infinity. In case of lower frequencies the communicating parties wouldn't be able to exchange data if they would be too close.

• Is there any proof of that? I mean close field can't communicate information? thnks
– HDE
Commented Nov 30, 2011 at 10:59
• @HDE Theoretically the information could be transmitted by close field but in order to do that you should "encode" the information into close field component. The electromagnetic field consists of close field component and far field component and most of communication standards (all that I know) exploit just far field component. Commented Nov 30, 2011 at 17:29

The real issue. I think, is data transmission rates.

I don't know what type of keying or data transmission are used at ELF, but, as I understand it data transmission rate is a big issue. When frequency rate is so low, it's hard to stick data onto.

FWIH data transfer rate at ELF is measured in words per hour, not words per second.

Normally the carrier frequency is modulated (amplitude or frequency) by a much lower frequency carrying the data.

If you decrease the ratio of data frequency relative to carrier frequency, you can reduce data error/incorrect signals.

For low fundamental frequency carriers signals, this significantly reduces the data rate below what many find useful.

It may be more efficient at these low frequencies to use spread spectrum techniques to transmit the data. You are then in effect using the bandwidth in a more efficient manner - and this generally has much better interference rejection.