Electromagnetic Frequencies

Analog Communications Channel – A communication channel in which the message being transmitted, for example voice, directly modulates the amplitude or frequency of a higher frequency RF or MW signal.

Antenna: A wire or set of wires used to send and receive radio waves.

Base Station: The combination of antennas and electronic equipment used to receive and transmit wireless telephone signals.

CDMA (Code Division Multiple Access) – A method of coding the digitized messages of several users and transmitting them at the same time using a single communication channel. Each user’s message is decoded independently of the others.

Cell Phone: A wireless telephone that sends and receives messages using radiofrequency energy in the 800-900 megahertz portion of the radiofrequency (RF) spectrum.

Cell Site: Another name for a cellular base station.

Cellular Base Station: Antennas and electronic equipment used to receive and transmit cellular telephone signals.

Cellular Phone System – A system for mobile wireless communication where blocks of frequencies (channels) can be reused by dividing a geographical area into hexagonal “cells” each of which contains a transmit/receive base station antenna. A mobile user within a cell communicates with the base station in that cell or an adjacent cell depending on the strength of the received signals. As the usermoves from cell to cell, the connection between the user and network is maintained by “handing-off” the user from one base station to another, i.e., switching to a channel assigned to that base station.

Cellular Phone: A wireless telephone that sends and receives messages using radiofrequency energy in the 800-900 megahertz portion of the radiofrequency (RF) spectrum.

Cordless Telephone: A portable telephone that transmits signals over a small distance to a receiver that is wired into the telephone network. Cordless telephones are generally used only in or around one’s home.

Digital Communication Channel – A communication channel in which the message is encoded as a series of “ones” and “zeros” (binary code). This can be done in several ways, but a common scheme has the phase of a component of the transmitted signal switched in discrete steps to represent the “zeros” and “ones,” respectively.

Directional Antenna – An antenna that radiates energy efficiently in a specific direction. For example, the energy from directional antennas used for personal wireless service, often called “high-gain,” “panel,” or “sector” antennas, is usually propagated in a relatively narrow beam in the vertical plane (of the order of 10 degrees) and typically 120 degrees in the horizontal plane.

Downlink – The communication connection (transmitted signal) from a base station to a mobile station.

Electromagnetic Energy: Waves of electrical and magnetic energy moving together through space. Also called electromagnetic radiation.

Electromagnetic Field: An area containing electromagnetic energy (electromagnetic radiation).

Electromagnetic Radiation: Waves of electrical and magnetic energy moving together through space. Also called electromagnetic energy.

Electromagnetic Spectrum: The collection of all electromagnetic energy arranged according to frequency and wavelength.

ERP (Effective Radiated Power) – A measure of how well an antenna concentrates the radiated energy in a specific direction. An analogy can be drawn in a comparison between an ordinary light bulb and a spotlight. At a given distance, the light that falls on a surface in the beam of a 100 W spotlight is much brighter than that from an ordinary 100 W bulb at the same distance, because the spotlight concentrates the light into a beam. Correspondingly, the light that falls on a surface that is not in the beam of the spotlight is much less than that from the ordinary light bulb at the same distance.

FDMA (Frequency Division Multiple Access) – A method for carrying multiple messages during a RF or MW transmission by encoding the messages of different users as modulations of different carrier frequencies.

Frequency: The number of waves passing a given point in one second. Measured in Hertz (Hz), or cycles per second.

GSM (Global System for Mobile Communications) – A hybrid TDMA/CDMA scheme widely used throughout Europe, and also becoming available in The USA.

Hertz: The unit of measurement used to describe the frequency of a wave. One Hertz (Hz) is equal to one cycle of the wave per second.

High-Gain Antenna – an antenna whose radiation pattern is concentrated in a more or less narrow beam, i.e. a “directional antenna”.

Ionizing Radiation: Very high energy electromagnetic radiation that strips electrons away from their normal locations in atoms and molecules.

Microwatt (µW) – a power of one millionth of a watt.

Microwave (MW) – An electromagnetic wave with a wavelength between about one millimeter and 30 centimeters corresponding to a frequency between 300 GHz and 1 GHz.

Microwaves: A subset of radio waves that have frequencies ranging from around 300 million waves per second (300 MHz) to three billion waves per second (3 GHz).

Milliwatt (mW) – a power of one thousandth of a watt.

Non-Ionizing Radiation: Levels of electromagnetic radiation that are too low to strip electrons away from their normal locations in atoms and molecules

Omni-Directional Antenna – An antenna that radiates energy power more or less uniformly over an angle of 360 degrees in the horizontal plane around the antenna. Sometimes called a “low-gain” antenna. The familiar “whip” antennas are omnidirectional in their radiation patterns.

PCS (Personal Communication Service) – A term used by cellular service providers for digital service primarily in the 1800 – 2000 MHz frequency band. The term distinguishes this newer wireless protocol from cellular service at lower frequencies.

PCS Phone: A wireless telephone that uses radiofrequency signals in the 1850-1990 megahertz (MHz) portion of the radiofrequency (RF) spectrum. PCS stands for portable communication system.

Power Flux – sometimes called “power density,” is a measure of the radiated power reaching unit area of a surface. The accepted unit for this parameter is watts per square meter (W/m-sq). However, the older measure milliwatts per square centimeter (mW/cm-sq) is still encountered. 1 mW/cm-sq is equivalent to 10 W/m-sq.

Radiation: (1) The emission and transmission of energy through space or through a material medium. (2) The radiated energy itself.

Radio Frequency (RF) – frequencies of electromagnetic waves between approximately 3 kHz (3,000 Hz) and 300 GHz (3 x 10¹¹ Hz). Sometimes, a distinction is drawn between radio waves, which have frequencies between 3 kHz and 1 GHz, and microwaves, which have a frequency between 1 GHz and 300 GHz.

Radio Waves: Electromagnetic energy with frequencies in the 3000 hertz (3 kHz) to 300 billion Hertz (300 GHz) portion of the electromagnetic spectrum.

Radiofrequency Energy: Another name for radio waves.

RF Energy: An abbreviation for Radiofrequency Energy.

SAR (Specific Absorption Rate) – A measure of the rate at which electromagnetic energy is absorbed by an exposed object. SAR, measured in watts per kilogram (W/kg), is the basic quantity from which modern RF and MW safety criteria (exposure limits) are derived.

Specific Absorption Rate: A measure of the rate at which RF energy is absorbed by the body.

TDMA (Time Division Multiple Access) – A method for combining the messages of several users on a single radio channel by assigning each user a different time segment of each transmit interval.

Telecommunications: The transmission of words, sounds, or images, usually over great distances, in the form of electromagnetic energy, for example by telegraph, telephone, radio, or television.

Telephone Network: The system of wires, fiber-optic cables, satellites, and transmission towers that transmit telephone messages from caller to receiver.

Transceiver - A term used to describe a communication device that can both receive (detect) signals, and transmit signals.

Uplink – The communication connection (transmitted signal) from a mobile station to a base station.

Telephone Transmission Tower: A telephone base station located on top of a tall, free-standing structure.

Wavelength: The distance covered by one cycle of a wave.

Wireless Telephone Base Station: The combination of antennas and electronic equipment used to receive and transmit wireless telephone signals. Sometimes called a base station.

Wireless Telephone: A hand-held phone with a built-in antenna that transmits signals through the air without a physical connection. Cell (cellular), PCS, mobile, car, and bag (transportable) phones are all considered wireless telephones. Cordless telephones used only in or around one’s home are not considered wireless telephones.