(The following is largely copied from an article on the same subject posted at the NPS web page.)
Most investigative effort in this community is focused on frequency. Whether via “full spectrum” photography, the latest EMF gadget, audio recorders, or DIY sensors and transmitters, the omnipresent trend is to find some telltale signature within the electromagnetic spectrum. There seems to be, unfortunately, a general misunderstanding of what is being “sensed” with our equipment. As usual, I am not claiming to have to have the one and only correct perspective on this subject. Nor do I intend to provide complete answers and information. I am asking the reader to evaluate any information they are given by taking on a little research of their own.
Whether we see it, hear it, or even feel it, energy as we perceive it, is part of the same spectrum; from static fields to slow (long wave length) approaching zero cycles per second and up to what we can assume is an infinitely fast (short wave length). “Bandwidth” is a range of frequencies within this spectrum associated with a specific topic. We are most familiar with bandwidths such as visual, audio, radio, infrared, and ultraviolet.
Static fields (those with essentially no measurable frequency) include; magnetics, batteries, and the potential charge that zaps our fingers when we reach for a door handle. An intriguing, yet seldom discussed, aspect of the EM Spectrum is brain waves; near 0 Hz up to about 60 Hz. Within this frequency range, we also find information covering the Schumann Resonance (frequencies associated with Earth’s magnetic field). I will not go into this sort of detail here but, I recommend anyone intrigued by paranormal events also look into frequencies of the brain and the Schumann Resonance. At 50 and 60Hz we find the most common frequency for household power. 20 Hz up to 20,000 Hz (20 kHz) is the
nominal frequency range for human hearing; also the likely range for EVP sources. Above 20 kHz we find bandwidths defined as radio and microwave. It is important to note that most EMF meters are designed to detect or measure frequencies from 20 Hz up into the microwave range. The intent being to monitor frequencies commonly used in our technologies which may damage our health. Beyond microwave we find, infrared, visual, and ultraviolet. All three will be discussed briefly later this week. Beyond ultraviolet we find x-ray, gamma, etc.
The “man-made frequency” misnomer:
Nature vibrates, typically with a sinusoidal wave shape. The EM spectrum is not man-made, it is entirely comprised of natural frequencies. Humans have found ways to utilize and manipulate certain frequencies into signals to enable technology. Our technology generally creates signal shapes other than sinusoidal and signal patterns intended to transfer information. There are no uniquely man-made frequencies, though signal patterns are often man-made. While determining the frequency of an EMF “spike” may ultimately be valuable in attempting to determine its origin, the frequency alone does not indicate a man-made origin.
A few links to useful information:
An excellent graphic showing the EM Spectrum (thanks to Sparc Para Analytics):