What is the shape factor value? ANS: 1. Suppose a receiver uses a 5-MHz IF frequency. Assuming high-side injection, what Suppose a SSB receiver requires an injected frequency of 1.
ANS: over 6. The transformer of a double-tuned IF amplifier has a Q of 25 for both primary and secondary. What value of kc do you need to achieve optimal coupling? What value of transformer coupling would a double-tuned MHz IF amplifier Compared to tuned circuits, ceramic and crystal IF filters do not require with optimal coupling need to get a bandwidth of kHz? ANS: fixed, constant 1. Analog signals cannot be sent using digital techniques.
Digitizing a signal can reduce distortion. Digitizing a signal can improve the signal-to-noise ratio. Quantizing is converting a sample of an analog signal to a binary number. Morse code is an example of a binary digital transmission system. Quantizing always introduces some error. Digital signals can be modulated onto an analog carrier.
Quantizing always introduces some "noise". Digitization removes noise and distortion from analog signals. The significance of quantizing noise increases as the number of bits per sample increases. A digital signal can be changed from a 1 to a 0 by noise. The dynamic range of a digital transmission system depends on the number of 8.
A regenerative repeater converts a degraded pulse into a new pulse. T bits per sample. TDM is easy to implement with digital signals. The bandwidth required by a digital transmission system depends on the number of bits per sample. Unlike analog, digital communications is not band-limited.
Companding allows improved dynamic range for a given bandwidth. The amount of digital data that can be sent is limited by the channel capacity C. The companding system used in America is known as "A-Law" companding. The digital data rate is limited by the bandwidth of the channel.
Companding is basically a linear process. The digital data rate is limited by the SNR of the channel. Companding can be done with analog circuitry. The digital data rate is limited by the number of levels transmitted. Digital companding is used by most modern telephone systems. The Shannon-Hartley theorem describes how to obtain the Shannon limit for With delta modulation, only one bit is transmitted per cycle. T transmission. Delta modulation is particularly well suited to rapidly changing analog signals.
Digital data can be sent through a channel no matter how low the SNR is, as long as it is not zero. Delta modulation is prone to "granular noise". Analog signals must be sampled before they can be sent in digital form. Adaptive delta modulation reduces the occurrence of "slope-overload". Mathematically, it is not possible to completely reconstruct a band-limited A disadvantage of adaptive delta modulation is that it requires a higher bit rate signal from only samples of the signal.
F than PCM. The Nyquist Rate is equal to half the highest frequency component of the analog Digital data is put onto a cable using a line code. T signal. Unipolar line coding requires DC continuity. Natural sampling is also called "flat-top" sampling. Flat-top sampling requires a sample-and-hold circuit.
The Manchester line code provides strong timing information. Aliasing occurs when the sampling rate is too high. The basic DS-1 signal consists of 12 voice channels. Foldover distortion occurs when the sampling rate is too low. In DS-1, each analog voice channel is sampled times per second. Sampling is actually a form of modulation.
In DS-1, the bit rate for each voice channel is 56 kbits per second. The output of a sampler is a PDM signal. A T-1 frame contains bits. The most commonly used digital modulation scheme is PCM. T-1 uses AMI. In PCM, the number of levels is the same as the number of bits. A T-1 cable can be twisted-pair copper wires.
Foldover distortion is caused by: a. A T-1 line runs at 1. In DS-1, bits are sometimes "stolen" from the voice channel to be used for The immediate result of sampling is: signaling. PAM c. PCM d. PDM Which of these is not a pulse-modulation technique: with fewer bits. PDM b. PWM c. PPM d. PPS Quantizing noise quantization noise : a.
The dynamic range of a system is the ratio of: 1. The first digital code was the: a. ASCII code c. Morse code b. Baudot code d. In digital transmission, signal degradation can be removed using: a.
Companding is used to: b. TDM stands for: c. Ten-Digital Manchester d. Time-Domain Multiplexing d. Ten Dual-Manchester In North America, companding uses: 4.
Hartley's Law is: a. In Europe, companding uses: 5. The Shannon-Hartley theorem is: a. Codec stands for: 6. The Shannon Limit is given by: a. Coder-Decoder c. Code-Compression a. Coded-Carrier d. A typical codec in a telephone system sends and receives: 7. The Nyquist Rate can be expressed as: a. Compared to PCM, delta modulation: 8.
Natural Sampling does not use: a. In delta modulation, "granular noise" is produced when: 9. Which is true about aliasing and foldover distortion? They are two types of sampling error. You can have one or the other, but not both. Aliasing is a technique to prevent foldover distortion. The number of framing bits in DS-1 is: d. They are the same thing. Which coding scheme requires DC continuity: A vocoder implements compression by: a.
AMI c. Manchester d. Manchester coding: d. Framing bits in DS-1 are used to: 3. In analog channels, the signal-to-noise ratio of an analog signal gradually The number of bits per sample in DS-1 is: channel. The number of samples per second in DS-1 is: 6. The bit rate for each channel in DS-1 is: 7. ANS: correct In DS-1, bits are transmitted over a T-1 cable at: a. A T-1 cable uses: ANS: error, noise a.
Manchester coding c. NRZ coding b. ANS: Time The number of frames in a superframe is: a. ANS: limited A typical T-1 line uses: a. ANS: Hartley's ANS: Shannon-Hartley Compared to standard PCM systems, the quality of the output of a vocoder is: a. ANS: half ANS: Quantizing ANS: 12 ANS: superframe ANS: 1, one ANS: higher The telephone switching hierarchy is being replaced by a "flat" network topology. A "twisted-pair" is twisted to minimize "crosstalk".
T ANS: 5 seconds 9. Use the Shannon-Hartley theorem to find the bandwidth required to send 12, bits per second if the number of levels transmitted is 8. In a local loop, the red wire is positive. F ANS: hertz In a local loop, the TIP wire is positive. What is the Shannon Limit of a channel that has a bandwidth of hertz and a signal-to-noise ratio of 15?
Local loops can carry voice signals in only one direction at a time. F ANS: 16 kbps Local loops carry DC current. What is the minimum required number of samples per second to digitize an analog signal with frequency components ranging from hertz to hertz? Local loops carry signaling information. Loading coils allow high-speed data loads to be carried on a local loop. What is the approximate dynamic range, in dB, of a linear PCM system that uses 12 bits per sample?
Typically, when a phone is on hook, a voltage of 48 volts appears across it. T ANS: 74 dB 6. What is the approximate data rate for a system using 8 bits per sample and When a telephone is off hook, the DC voltage across it can drop substantially running at samples per second? T ANS: 64 kbps The DC resistance of a telephone is about ohms.
If bits were "stolen" from every DS-1 frame, what would the useable data-rate be for each channel in the frame? Assuming maximum input and output voltages of 1 volt, what is the output DTMF uses sets of 3 tones. F Chapter 8: The Telephone System The technology to "dial" telephone numbers was invented in A telephone from could not work on today's public switched telephone The central office uses 24 volts AC at 20 hertz to cause a telephone to ring. F network. The local-loop is full-duplex.
The public switched telephone network is changing from an all analog to a mostly digital system. Telephones usually contain a hybrid coil or an equivalent circuit. A LATA is a local calling area. To allow for "sidetone", a hybrid coil should be slightly unbalanced.
A feature of the public switched telephone system is that calls cannot be The signal levels in analog telephone systems have increased substantially over "blocked". F the past years. Telephones connect to the central office via trunk lines. The signal levels in modern analog telephone systems are still based on 19th- century technology. Most local loops still use copper wire. To allow multiplexing, the bandwidth of voice-grade telephone signals is 2.
PSTN stands for: deliberately restricted. Public Switched Telephone Network b. Private Switched Telephone Network The net gain of a telephone system must be greater than 0 dB for an acceptable c. Primary Service Telephone Network signal level. Primary Service Telephone Numbers Too much gain in a telephone system causes "singing".
POTS stands for: a. Private Office Telephone System Echo suppressors prevent oscillations on long-distance telephone circuits. Primary Office Telephone Service c. Primary Operational Test System Echo suppressors can be switched off by a subscriber's equipment. Plain Old Telephone Service C-message weighting increases the bandwidth of a local loop. LATA stands for: a. Local Access and Transport Area c. Local Area Telephone Access The reference level for measuring noise in a telephone system is 10—12 Watts.
Local Access Telephone Area d. Local Area Transport Access In a telephone system, signal strength is given relative to the zero transmission 5. A LATA is a: loss point. Central offices are connected by: DS-1 can be used to carry digital data that did not originate as a voice signal. When using DS-1 to carry data, it is common to use each channel to carry 64 kbps.
Local loops terminate at: a. Digital carriers up to T3 can use copper wires. Call blocking: a. Every "in-channel" signal is also an "in-band" signal. In telephony, POP stands for: a. Post Office Protocol c. Power-On Protocol Common-channel signaling is being replaced by the more modern MF signaling. Point Of Presence d. The cable used for local loops is mainly: Common-channel signaling reduces opportunities for stealing telephone service.
FITL stands for: a. Framing Information for Toll Loops c. Framing In The Loop Fiber In the Toll Loop d. Fiber-In-The-Loop DTMF stands for: a. Digital Telephony Multiple Frequency The range of DC current that flows through a telephone is: b. Dial Tone Master Frequency a. Dual-Tone Multifrequency b. Loading coils were used to: In DS-1, bits are "robbed" in order to: a. The separation of control functions from signal switching is known as: b. ESS ISDN stands for: a.
Integrated Services Digital Network The typical voltage across a telephone when on-hook is: b. Information Services Digital Network a.
Integrated Services Data Network b. Information Systems Digital Network The typical voltage needed to "ring" a telephone is: Basic ISDN has not been widely adopted because: a. The bandwidth of voice-grade signals on a telephone system is restricted in d.
ADSL stands for: b. All-Digital Subscriber Line c. Allocated Digital Service Line b. Asymmetrical Digital Subscriber Line d. Access to Data Services Line VNL stands for: a. Signal loss is designed into a telephone system to: a. The reference noise level for telephony is: 1.
The number of voice channels in a basic FDM group is: 2. Basic FDM groups can be combined into: 3. In telephone system FDM, voice is put on a carrier using: central office. SSB b. DSBSC c. PDM d. PABX stands for: 5. Power Amplification Before Transmission to an overload of lines being used. Public Automated Branch Exchange d. Public Access Branch Exchange 6. ANS: digital SLIC stands for: a. Single-Line Interface Circuit c. Subscriber Line Interface Card 7.
Standard Line Interface Card d. ANS: tip ANS: green ANS: seized ANS: common-channel ANS: packet ANS: TE1 ANS: asymmetrical ANS: conditioned ANS: suppressor 1. For a certain telephone, the DC loop voltage is 48 V on hook and 8 V off hook. If the loop current is 40 mA, what is the DC resistance of the local loop? ANS: C-message 2. If the loop current is 40 mA, what is the DC resistance of the telephone? Which two DTMF tones correspond to the digit "1"?
Use the table in the text. In synchronous transmission, control characters in the data require special ANS: Hz and Hz handling, but flag sequences in the data do not. Calculate the dB of VNL required for a channel with a 3 ms delay. T ANS: 1 dB HDLC is a bit-oriented protocol. If a telephone voice signal has a level of 0 dBm, what is its level in dBrn? ANS: 90 dBrn When receiving digital data, it is possible to detect errors, but not to correct them. If C-weighting produces a dB loss, what would the signal level be in dBrnc0?
In digital data transmission, bad frames are usually retransmitted. CRC codes are particularly good at detecting burst errors. Hamming codes allow errors to be corrected without requiring retransmission. T Chapter 9: Data Transmission All schemes to detect errors require adding extra bits to the data being transmitted.
Huffman codes are as good as CRC codes at detecting errors, but are faster. Data can be sent either in serial format or in parallel format. Run-length encoding is a data-compression technique. For practical reasons, virtually all data communications is done in serial format. A "cipher" is, essentially, a secret code. The first binary code was invented in Both "private-key" and "public-key" encryption always require the addition of 4.
A character code is the same as a data code. T extra bits to the data. The old Baudot code is no longer used. An advantage of public-key encryption is that it is not "computation-intensive", meaning a computer doesn't have to do many numerical calculations to unencrypt 6.
How fast data can be transferred is independent of the character code used. F decrypt the data. Both synchronous and asynchronous transmission require bit timing. A "digital signature" does not require the use of encryption. There is no "framing" in asynchronous transmission. A "mark" is the same as a binary 1. In practical terms, parallel data transmission is sent: Digital modulation is sometimes called "keying". Due to the "bursty" nature of most channel noise, simple parity is more or less useless.
The five-level teletype code was invented by: a. Western Union An advantage of using a UART is that "buffer overflow" cannot happen. Emile Baudot Synchronous transmission is much more efficient than asynchronous 3. Data codes are also called: transmission.
In synchronous transmission, the data stream is used to "lock" the receiver's clock onto the transmitter's clock. Digital data that is not being used to carry characters is called: a. FIGS data c. Bit-oriented protocols are being replaced by the newer character-oriented b.
Character codes include: To maintain synchronization in synchronous transmission: a. ASCII stands for: d. American Standard Character-set 2 b.
American Standard Code for Information Interchange HDLC: c. American Standard Code 2 a. Alphanumeric Standard Code for Information Interchange b.
The use of flags in SDLC requires: a. FEC b. ARQ 8. LF stands for: The initials ARQ are used to designate: a. Line Feed c. Line Forward a. Link Feed d. Link Forward b. UART stands for: d.
Universal Asynchronous Receiver-Transmitter b. Unidirectional Asynchronous Receiver-Transmitter ARQ is used to: c. Unaltered Received Text a. Universal Automatic Receiver for Text b. In asynchronous transmission, the transmitter and receiver are: d.
FEC stands for: c. Fixed Error Control c. Forward Error Correction d. Forward Error Control d. False Error Condition In asynchronous transmission, the time between consecutive frames is: VRC is another name for: a.
ARQ c. LRC d. CRC stands for: In synchronous transmission, the frames are: a. Control Receiver Code c. Cyclic Redundancy Check a. Correct Received Character d. Cycle Repeat Character b. Huffman codes: d. Synchronous transmission is used because: c. Run-length encoding is used to: d. In synchronous transmission, the receiver "syncs-up" with the transmitter by using: Public-key encryption: a. SDLC stands for: Synchronous Data Link Control c. Synchronous Data Link Character transmission.
Synchronous Data Line Control d. HDLC is: ANS: Burst 5. ANS: stop ANS: even 8. ANS: mark, binary 1 ANS: burst 9. ANS: transitions Token passing can be implemented as a ring or as a bus.
T ANS: computation A token is used to control access to the network. A token is generated by a node wishing to access the network. How many different characters could be encoded using a six-bit code?
On a bus network, all traffic shares a common channel. T ANS: 64 CSMA networks must deal with "contention". Token-passing networks must deal with "collisions" between two tokens. F ANS: 20 hex 32 decimal A "collision" will take a CSMA network down. If an asynchronous frame is used to send ASCII characters in the form of bytes 8 bits , what is the shortest time it could take to send characters if each bit in a Token rings never have collisions.
T frame is 1 msec long? ANS: 10 seconds CSMA works best when traffic is relatively light. Suppose an asynchronous frame holds 8 bits of data, a parity bit, and two stop A token-ring network can be implemented with a bus topology. T bits it could happen. Calculate the efficiency of the communication system. Suppose a synchronous frame has 16 bits of non-data in the front and a bit Token-ring networks usually operate at megabits per second.
F BCC at the end. The frame carries bytes of actual data. Most LANs are based on the Ethernet type of network. T ANS: Ethernet was originated by Microsoft with participation by Intel. IEEE T Chapter Local Area Networks Ethernet-type networks are limited to a maximum speed of Mbits per second.
Classic Ethernet is no longer used for new networks. The maximum extent of a local area network is one building.
Originally, Ethernet used 10Base2 coaxial cable. An organization could have several local area networks in the same room. LANs can allow several people to access the same file at the same time. The "" in BaseT designates the supported bit rate. LANs often use "dumb" terminals as workstations.
The "Base" in BaseT indicates the cable carries an unmodulated signal. On a circuit-switched network, a data stream has a channel all to itself for the duration of the connection. The "T" in BaseT indicates the cable is Thick coax. A "node" is a workstation or PC connected to a network. In a star network, if one node fails, the entire network goes down. Ethernet type LANs use token passing. Hubs are, by definition, passive. In CSMA, a node must "listen" to the channel before trying to use it.
Carrier Detection c. Collision Detection Carrier Delay d. Collision Delay Ethernet cannot use fiber-optic cables. The Internet is: a. Most LANs: Longer packets means more bits must be retransmitted after a collision.
Dumb terminals are still used: a. A NIC gives a unique address to a node on a network. If coax is used, the ends must be left open to avoid reflections. In a circuit-switched network: a. Typically, a NIC requires a 4-wire cable to connect to a hub. Standard Manchester line encoding can be used up to Mbits per second.
Each computer on a network is called a: a. Compared to a hub, a switch reduces the chances for a collision. The key feature of a star network is that individual workstations are connected F to: a. Network software is generally independent of the network topology. The same network software can be used on a token-passing network and on an On networks, long messages are divided into "chunks" called: Ethernet LAN.
To a user on the network, a hard drive on the server looks like it is on the workstation. When two or more PCs try to access a baseband network cable at the same time, it is called: In a client-server network, each node takes a turn at being the server.
Software that runs a client-server network must have true multitasking ability. CSMA stands for: a. Client-Server Multi-Access c. Carrier Server Master Application One type of network that never has a collision is: b. Carrier Sense Multiple Access d. CSMA c. Ethernet d. In an Ethernet-based network, a switch can be used to reduce the number of: UTP stands for: a.
Untwisted-Pair copper wire b. Unshielded Twisted-Pair copper wire c. Uninterruptible Terminal Packet The effect of too many collisions is: d. Unicode Text Packet a. Compared to twisted-pair telephone cables, CAT-5 cables: a. MAU stands for: b. Multistation Access Unit c. Multiple Auxiliary Units b. Multiple Access Unit d. A hub: a. The standard that describes Ethernet-type networks is: b. EIA c. Ethernet was invented by: A switch: a.
IBM c. Xerox a. INTEL d. Digital Equipment Corporation b. Manchester encoding c. NRZ encoding b. Three-Level encoding d. AMI encoding An advantage of using a switch instead of a hub is: a.
A BaseT cable uses: b. RGU coaxial cable c. The word "Base" in 10BaseT means: Broadband LANs: a. Using one node in the network to hold all the application software is done in: a. Record locking is used to: a. The software that runs a client-server network must be: a. UNIX-based c. NIC stands for: b. Novell certified a. Network Interface Card c. Network Interface Code b. Network Interface Cable d. Network Internal Code A "thin" client is: a.
ANS: topology 1. Explain how a network can be a physical bus but a logical ring. ANS: A token-passing network sends the token from node to node in a 6. So it doesn't matter how the physical connection is ANS: token made. It still works like a token-passing ring. What is the key difference between a hub and a switch?
Libreng Librong Pang-inhinyero. Electronic Communication Systems Communications. Electronic Communication Systems. Now in its second edition, Electronic Communications Systems provides electronics technologists with an extraordinarily complete, accurate, and timely introduction to all of the state-of-the-art technologies used in the communications field today.
Comprehensive coverage includes traditional analog systems, as well as modern digital techniques. Extensive discussion of today's modern wireless systems- including cellular, radio, paging systems, and wireless data networks- is also included.
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