Scan Receiver - A receiver that resides in the base station that is dedicated to measure mobile's signal strengths. These measurements are used in the handoff process (but not in the power-up/power-down process, which is handled by each voice transceiver).

Sector-Receive Cell Site - Six or three directional antennas that are used at a cell site to get additional gain required to serve mobiles. A mobile could move completely around a Sector-Receive cell site and never change channels, but would change antennas.

Sector-Sector Cell Site - The cell is broken up into two or more independent sectors that each have their own transmit and receive antennas. A mobile moving around a Sector-Sector cell would change channels (Intra-cell handoff)

Selectivity - The ability of a receiver to reject interfering signals close to the desired carrier frequency.

Sensitivity - The ability of a receiver to operate on very weak RF signal levels.

SHF - Super High Frequency. A signal in the frequency range of from 3 to 30 GHz.

Sidetone - An attenuated portion of the transmit audio returned to the originator. Can be intentional as all phones produce some sidetone and is caused by unbalanced 2-to-4 wire hybrids.

Signal-to-Noise - The ratio of the magnitude of the signal to that of the noise with no signal present, usually expressed in dB.

Signaling Tone (ST) - A 10 kHz tone transmitted by the mobile station on a voice channel to (1) confirm channel change orders (HO tone, 50ms ST), (2) request a flash-hook by the mobile (400ms ST), (3) mobile alert (continuous ST), (4) mobile ending call (1.8sec ST).

SIM - Subscriber Identification Module. A credit card size card which is owned by a subscriber, who slides it into any GSM handset to transform it into 'their' phone. It will ring when their unique phone number is dialed; calls made will be billed to their account; all options and services connected; voicemail can be collected and so on.

SMR - Specialized Mobile Radio. FCC has allocated the 896-901 MHz band (800 MHz band) which uses two paired 25 KHz channels and the 935-940 MHz band (900 MHz band) which uses two paired 12.5 KHz channels. Ten 20 channel blocks have been allocated in these frequency bands. 900 MHz SMR is primarily used for radio dispatch , paging and wireless data communications.

Source Cell - The cell that a mobile is leaving during the hand off process.

Source Channel Falsing - A condition that exists when co-channel SAT exists on the source channel during handoff, so that source channel does not squelch during the handoff process. This results in noise during the handoff process (after the handoff order) that can be heard by both the landline and mobile parties.

Spectrum - The electromagnetic spectrum. A continuous group of electromagnetic frequencies.

Spread Spectrum - A communication technique that spreads a signal bandwidth over a wide range of frequencies for transmission and then de-spreads it to the original data bandwidth at the receiver.

Squelch Circuit - A radio receiver circuit which disables the audio path when the incoming signal is below a predetermined threshold. When the radio signal from a transmitter is too weak to produce a quality audio signal, the receiver will shut off or "squelch."

Standby time - The amount of time you can leave your fully charged cellular portable or transportable phone turned on before the phone will completely discharge the batteries.

Station Class Mark (SCM) - Indicates mobile station type (mobile/transport), and if station has DTX.

Subaudio - Frequencies below the audio bandwidth for speech, which is 300 to 3000 Hz.

Subscriber - The mobile user of the cellular system.

Subscriber Files - Stored at the MTSO and contains all information pertaining to each subscriber. Includes mobile number, home service location, last known location, type of mobile, service denial flags, and special feature options available to that subscriber.

Super Audio - Frequencies above the audio bandwidth, which is 300 to 3000 Hz.

Superheterodyne - The mixing of two signals producing a third signal. Almost all other receivers) utilize an oscillator, producing a signal which is mixed with the incoming radio signal from the receiver antenna to produce a lower frequency signal (the IF signal).

Supersonic Noise Squelch - A fairly popular method of muting the audio output of a receiver when the supersonic noise reaches a preset level. The assumption is that noise buildup above the audio passband (20 to 30 KHz range) is an indication that the signal to noise ratio of the system is inadequate to produce a usable audio signal.

Supervisory Audio Tone (SAT) - One of three tones (5970, 6000, and 6030 Hz) that are transmitted by the base station and transponded by the mobile station. Used to evaluate the complete radio path, both Forward and Reverse Voice Channels. The SAT received by the mobile unit is actually regenerated by the mobile unit with the same amplitude and noise associated with the actual received SAT.

System Identification (SID) - A unique digital code assigned to each cellular system. The home system of each mobile is stored in it's internal memory so that the mobile knows when it is a roamer (outside it's normal service area).

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