Field Intensity Meter

(field strength meter), an instrument for measuring the intensity of the electric component (less frequently the magnetic component) of a field or the energy flux density of electromagnetic radiation. Such radiation may be emitted by sources of sinusoidal and modulated oscillations, including some sources of radio interference.

A distinction is made between field intensity meters used to measure weak and strong fields. The first type is used to study the propagation of radio waves, to evaluate the quality of shielding of radiation sources, to measure antenna directivity patterns, to detect and measure spurious radiation of transmitting equipment, and to search for sources of radio interference and to measure their radiation intensity. The second type is used mainly to measure the energy flux density of microwave radiation to determine whether the density is within the permissible limits established by medical and biological safety standards.

A field intensity meter consists of an antenna, usually a broadband rod, dipole, or ferrite antenna (for ultrahigh frequencies, a horn antenna is used), calibrated in terms of effective height or effective area, and a device that measures the intensity or power of the received oscillations. In field intensity meters for weak fields this device is a frequency-selective superheterodyne radio receiver that operates at frequencies of 0.015–1000 megahertz or higher. The sensitivity of such receivers is 0.5-10.0 microvolts; their total error is 2-4 decibels. Measurement results are read from a pointer indicator at the output of the radio receiver; headphones are often used as indicators of radio interference. Medium and strong signals (0.1 microwatt to 10 milliwatts, with a frequency of 0.1–40.0 gigahertz) are measured by thermistor or thermoelectric power meters. The total measurement error of such field intensity meters is 20-30 percent.