Extech Instruments 480836 User Manual page 3

2.0 - Introduction
2-1 Fundamentals
Electromagnetic Radiation
This meter is used to indicate radiated electromagnetic fields. Wherever there is
a voltage or a current, electric (E) and magnetic (H) fields arise. Examples
include the electromagnetic fields from radio broadcasting and TV transmitters.
Electric Field Strength
This is a field vector quantity that represents the force (F) on an infinitesimal unit
positive test charge (q) at a point divided by that charge. Electric field strength is
expressed in units of volts per meter (V/m).
Use the units of electric field strength for measurements in the following situations:
• In the near-field area of the source
• Where the nature of the electromagnetic field is unknown
Magnetic field strength (H) :
This is a field vector that is equal to the magnetic flux density divided by the
permeability of the medium. Magnetic field strength is expressed in units of
amperes per meter (A/m).
Power density (S) :
Power per unit area in the direction of propagation, usually expressed in units of
watts per square meter (W/m2) or, for convenience, units such as milliwatts per
square centimeter (mW/cm2).
The characteristic of electromagnetic fields :
Electromagnetic fields propagate as waves and travel at the speed of light (c).
The wavelength is proportional to the frequency.
λ(wavelength) =
Near-field is assumed if the distance to the field source is less than three
wavelengths. For far-fields, the distance is more than three wavelengths. In the
near-field, the ratio of electric field strength (E) and magnetic field strength (H) is
not constant, so measure each separately. In the far-field, however, it is enough
to just measure one field quantity, and compute the other accordingly.
2-2 Application
High frequency (RF) electromagnetic wave field strength measurement
Mobile phone base station antenna radiation power density measurement
Wireless communication applications (CW, TDMA, GSM, DECT)
RF power measurement for transmitters
Wireless LAN (Wi-Fi) detection, installation
Spy camera, wireless bug finder
Cellular/Cordless phone radiation safety level
Microwave oven leakage detection
Personal, environmental EMF safety
c (speed of light)
f (frequency)
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