This is the Review Notes in Wire and Wireless Communications System as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Summary of Important Wire and Wireless Communication Review Notes
10 to 100 μW – typical speech power
The maximum intelligibility for voice frequency is located between 1000 and 3000 Hz
The maximum voice energy is located between 250 and 500 Hz
Volume unit meter – a device used to measure speech volume
By definition, for a sine wave 0 dBm = 0 V.U
Presently, 300 to 3400 Hz is the “standard” frequency bandwidth for voice transmission
AWG # 19 is commonly used wire for subscriber loop design
The resistance limit for No.2 Crossbar Exchange (US) is 1300 Ω
AWG # 26 has typical loss of 0.51 dB/1000 ft
4 kHz is the standard voice channel spacing
Reflectometer is used to measure SWR
Singing – an undesired self-sustained oscillation in a system, generally caused by excessive positive feedback
IF stage increases the selectivity of the circuit in an AM receiver
The sensitivity of radio receiver amplify weak signal and produce a desirable intelligence at the output speaker
Full-duplex transmission means two-way simultaneous transmission
Multi drop line – a line or circuit interconnecting several stations
A passive attenuator is an electronic device which reduce signal strength by a specified amount in dB
Roaming – the signal quality of the cells is constantly monitored by the base station, when the quality of the calls drops below a certain specified level, the base request the MTSO to try and find a better cell site.
MIN – a digital identification associated with a cellular system
Facsimile transmit a standard page of 25 seconds
Electrolytic recording – a kind of recording is used in facsimile
Skewing – a type of distortion a facsimile produces when it becomes out of synchronization
Acoustic coupler – a device that converts electric signal signals into audio signals, enabling data to be transmitted over the public telephone network via a conventional telephone handset
Crosstalk causes a herringbone pattern in facsimile
The capture effect in an FM receiver causes a stronger signal to dominate over a weaker signal on the same frequency
Hybrid circuit – a device that converts a 2-wire circuit to a 4-wire circuit
Decision theory is deciding between a set of hypotheses when given a collection of imperfect measurement
Jaynes maximum entropy principle of a data reduction says that when reducing a set of data into the form of a underlying mode, one should be maximally non-committal with respect to missing data
Estimation is selecting the best value of a parameter from a continuum of possible values when given a collection of imperfect measurements
Discrete channel – combination of modulator, channel, and detector
The frequency band of DECT is 1.88 – 1.90 GHz
Each DECT system can support 12 simultaneous calls
A DECT radio transceiver can assess 120 simultaneous calls at any given time
The AGC voltage of a radio receiver is always DC, but may have either polarity
Concentrator – a switching system that lets a large number of telephone or data processing subscribers use a lesser number of transmission lines or a narrower bandwidth
If you find that an SAW filter output is 6 dB down from the input of a receiver during test, this is normal
A triple conversion superheterodyne receiver, diode mixer stages are operated in the nonlinear region
Leased line – a permanent circuit for private use within a communication network
If two FM signals of different strengths are received on the same frequency only the stronger will appear in the AF output
Cellular mobile system was first operated in 1983
TACS is a cellular system with 1000 channels
Supervisory Audio Tone (SAT) has 6000 Hz frequency
GSM uses GMSK digital modulation technique
The power output of Personal Communications System (PCS) is 10 mW
RG-58 cable has a loss of about 3 dB at cellular frequencies up to 15 feet length
Pilot carrier signals – the signals designed to keep the receivers and transmitters aligned
When a line and a load are match, the reflection coefficient is zero
When line is terminated in an open circuit load, the reflection coefficient is unity
The telephone set is powered by the central office on the ring side at -42 to -52 Vdc
The telephone voice band frequency is from 300 to 3400 Hz
Green wire is used to transmit the signal
The corresponding frequencies for digit 7 in the touch tone telephone is 852 & 1209 Hz
The physical connection between the telephone set and the switching equipment is called the subscriber loop
The local loop of a telephone system is a two-wire or four-wire communication circuit between the customer’s premise and the central office
Dial long lines, voice repeater, and loop range extender are used in long loop design
A two-wire circuit is a circuit usually in the subscriber loop, between the telephone set and the local central office
1 mW is equal to 90 dBm
First selector responds to the request of a subscriber by sending a dial tone
Section – the other name of Class 2 office in the North American Switching Plan
A cell in the cellular telephone system means small area
MTSO is the linking point between cell phone and regular telephone
The typical power output of a cellular phone is 3 W
When a single cell is subdivided into smaller cells the process is called cell splitting
The first cell shape is a circle
In order to provide 100% coverage without overlap, cellular telephone system can use hexagon cell shape, triangle, or rectangular
The beamwidth of the reflector of the receiving antenna in the base station is 60 degrees
A cellular phone operates on full duplex
Cellular phone transmit in the band from 825 to 845 MHz
Cell phone receives in the band from 870 to 890 MHz
The frequency separation between the transmit and the receive channels 45 MHz
For channel 1, transmit/receive frequency is 825.015/870.015 MHz
The number of transmit/receive channels in the cellular system is 666
The transmission range of cellular telephony is generally about 80 km
Large service area is not an advantage of a cellular telephone system
When the message is transferred from one cell site transmitter to another cell site transmitter as the caller crosses a boundary hand off process take place
The sensitivity of a cellular receiver is 50 dB
The frequency deviation of the cellular telephone system is +-12 kHz
Hailing channel is otherwise known as calling channel
Erlang is equal to the number of simultaneous calls originated during a specific hourly period
All of the cell base stations are linked together by MTSO which serves as the central office and management node for the group
Cell site – provides interface between the mobile telephone switching office and the mobile units
A phone call over the cellular network actually requires full duplex channels
Volume – a method of expressing the amplitudes of complex non-periodic signals such as speech
Echo is a signal returned to the talker after making one or more round trips between the talker and the listener
Echo suppressor is a voice operated device that inserts a high loss in the opposite direction of transmission of the talking party
Double spotting is picking up of the same station at two nearby points on the receiver dial
Crosstalk – when one channel picks up the signal carried by another channel
TPS type of connector arrangement wherein a customer may move to another location and still retain the same telephone number
An advantage of sidetone is that is assures the customer that the telephone is working
Half-duplex – radio communications between points using a single share frequency
TDM – the transmission of information from multiple sources occurring on the same facility but not at the same time
When human voice and music are transmitted, the type of communication employed is known as radiotelephony
Printed documents to be transmitted by fax are converted into a baseband electric signal by the process of scanning
Charge couple device is the most commonly used light sensor in a modern fax machine
In FM fax, the frequencies for black and white are 1500 and 2300 Hz respectively
Group 2 fax uses vestigial sideband AM
The most widely used fax standard is Group 3
Group 3 fax uses QAM modulation
Most fax printers are of thermal type
Facsimile standards are set by the CCITT
Satellite weather photos are commonly transmitted by radio fax
The transmission speed of group 4 fax is 56 kbits/s
Mobile telephone switching office is the master control center for cellular telephone system
Each cell site contain a repeater
Trunk – a telephone line connecting two central offices
Cellular telephones use full-duplex type of operation
The maximum frequency deviation of an FM cellular transmitter is 12 kHz
The output power of a cellular radio is controlled by the MTSO
When the signal from a mobile cellular unit drops below a certain level, the unit is “handed off” to a closer cell
In a cellular radio, the duplexer is a pair of sharp bandpass filters
On a telephone system, the loop is open during on-hook condition
For every button pressed on a touch-tone telephone, two audio-frequency tones are transmitted to the C.O.
Erlang B is the traffic model about blocked calls clear condition specified blocking probability
A touch-tone telephone generates 8 audible tone frequencies
935 – 960 MHz – the base-to-mobile frequency assignment of a GSM system
A voice-grade channel is suitable for transmission of signals with a frequency ranging from 300 to 3400 Hz
The bandwidth of cellular CDMA system is 1.23 MHz
A communication link is a channel or circuit intended to connect other channels or circuits
Poisson – block calls held condition specified the held probability at a time period equal to an average holding time
Echo – a wave which has been reflected or otherwise returned with sufficient magnitude and delay for it to be perceptible in some manner as a wave distinct from that directly transmitted
The system used by Personal Communication Network (PCN) is modified GSM
Termination refers to load connected to the output end of a transmission line
The multiple access used by Digital European Cordless Telephone (DECT) is TDMA
Erlang C – blocked calls delay condition specified delay probability
GFSK – the modulation technique used by DECT
A four-wire circuit is used between serving central offices for long-distance connections, with one pair being used for each direction of transmission
Cellular CDMA system uses BPSK modulation
PABX means Private Automatic Branch Exchange
The voted cellular digital standard at TIA is Digital AMPS
The number for channels for Band A and for Band B in Digital AMPS is 416
The mobile-to-base frequency assignment for GSM system is 890 – 915 MHz
The range of a cellular CDMA system is 13 miles
In a cellular system, radio capacity is used to measure the spectrum efficiency
Singing echo is completely out of control
Loop extender increase the battery voltage on a loop and extends its signaling range
Under ordinary circumstances, the CCITT recommends that the number of circuits in tandem must not exceed 12
The system capacity of AMPS is 100,000
NAM means Numeric Assignment Module
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