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NFER®, or "near field electromagnetic ranging" technology, involves a generally overlooked, and often times deemed irritating aspect of radio frequency, or "RF," behavior. The majority of conventional radios operate in the 'far field', a designation that, combined with the 'near field,' makes up the boundary regions of electromagnetic radiation emitted from an antenna. NFER® technology exploits peculiar behavior exhibited in the near field. These peculiarities manifest within about half a wavelength of the antenna, or in the field 'near' the antenna. To understand NFER Technology the physics behind it must initially be explained: First know, radio signals are electromagnetic waves, meaning: a radio wave is the combination of an electric wave and a magnetic wave. These waves leave the antenna and are offset by ninety degrees. However, by the time both the electronic and magnetic waves have transmitted from the antenna to travel just half the distance of a wavelength, that degree of offset has decreased to almost zero. This phenomenon is the essential principle behind NFER® technology.  The figure above is a graphic representation of how the phases of the electric and magnetic waves behave in the 'near field' of a small electric antenna. The green illustration is of the change in phase of the magnetic wave as it travels away from the transmitting antenna. The red curve illustrates the same change in the electric wave. The blue curve is fundamental key to NFER® technology. This blue curve illustrates the difference between the phase of the two waves, (the green curve minus the red curve equals the blue curve).
Example depicting the NFER® system's ability to measure distance: Begin with a receiver that is capable of detecting both electric and magnetic waves.
Next, add a transmitter (antenna) that is an unknown distance away from the receiver.
The transmitter periodically emits a signal at 1000KHZ. These signals are gathered by the receiver.
Now the receiver measures the difference in the phases of the electric and magnetic waves and finds the solution to be 30 degrees.
(Using the red curve in the figure, the extrapolated distance between the transmitter and receiver is 0.185 wavelengths.) An RF wavelength at 1000 KHz is 983.8 feet. Multiplying 0.185 times 983.8 reveals that the distance between the transmitter and receiver is 182 feet.
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