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ADC - Analog to Digital Converter.

Adjacent channel interference - Refers to interference caused by the energy from a transmitting channel spilling over into an adjacent channel. This interference can be minimized by applying filters to the transmitting and receiving ends or by simply using non-adjacent frequency channels within a cell. Cellular systems typically transmit on non-adjacent frequencies within a cell in order to prevent adjacent channel interference.

Airtime - Actual time spent talking on the cellular telephone. Most carriers bill customers based on how many minutes of airtime they use each month.

AJ - Anti-Jam. A communication signal that is designed to resist interference or jamming.

Alert - Constant 10 KHz signaling tone sent on the reverse voice channel (by the mobile), in an analog conversation, while the mobile phone is ringing.

Alphanumeric - A message or other type of readout containing both letters ("alphas") and numbers ("numerics"). In cellular, "alphanumeric memory dial" is a special type of dial-from- memory option that displays both the name of the individual and that individual's phone number on the cellular phone handset.

AM - Amplitude Modulation. The simplest carrier modulation technique where the RF carrier's amplitude envelope is modulated.

AMPS - Advanced Mobile Phone System. The current analog cellular FM system in North America. It uses 30 KHz channels and signaling is done superaudio.

Analog - The traditional method of modulating radio signals so that they can carry information. AM (amplitude modulation) and FM (frequency modulation) are the two most common methods of analog modulation. Analog modulation techniques have been around for more than 50 years and offer a proven, known method of using analog, but the switch to digital is already underway.

ANSI - American National Standards Institute. The ultimate accolade for any standard is ANSI certification. This does not mean that ANSI has reviewed the standard, but that it has been circulated widely throughout the industry and that it conforms to their document design and publication guidelines.

ARDIS - A wireless two-way data network jointly owned and operated by Motorola and IBM.

Attenuation - Weakening of the RF signal due to being partially blocked or absorbed. Attenuation is heavily dependent on the frequency of the RF transmission and on the physical characteristics of the material that the transmission interacts with. For example, high frequency microwave transmissions are severely attenuated by rain, but lower frequency cellular transmissions are not.

Auto-correlation - A measure of the similarity between a signal and a time-shifted replica of itself; a special case of cross-correlation. The auto-correlation function is the theoretical basis of direct sequence spread spectrum.

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