Term
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Definition
| The process, or result of the process, of modifying any characteristic of an information signal or carrier signal so that it varies in step with the instantaneous value of another information signal (analog, data, intelligence, or signal). |
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Term
| List one example each of analog-to-digital and digital-to-analog techniques. |
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Definition
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Term
| What are the two basic types of modulation? |
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Definition
(1) Analog modulation
(2) Digital modulation |
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Term
| What are the three basic types of analog modulation? |
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Definition
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Term
| What are the three basic types of analog modulation we use to convert a digital signal? |
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Definition
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Term
| What is the simplest form of PSK? |
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Definition
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Term
| What analog modulation technique is similar to QPSK? |
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Definition
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Term
| Why is DPSK better than PSK? |
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Definition
| Easier to implement and more robust. |
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Term
| What are the four basic types of pulse modulation? |
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Definition
(1) PAM
(2) PDM
(3) PPM
(4) PCM |
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Term
| How does ADPCM differ from PCM? |
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Definition
| Amplitudes are represented using 4-bit values (rather than the 8 bits used in PCM), and a 32 Kbps data-transfer rate is used (rather than 64 Kbps, as in PCM). |
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Term
| How does ADM differ from DM? |
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Definition
| ADM is a variation of DM where a signal's step size may vary from sample to sample. |
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Term
| What is a simple form of ADM? |
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Definition
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Term
| What frequencies are present at the output of an AM modulator? |
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Definition
(1) Carrier frequency
(2) Carrier plus modulating frequency
(3) Carrier minus modulating frequency |
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Term
| What component(s) of an AM modulated sine-wave carries information signals? |
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Definition
| Upper and lower sidebands |
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Term
| What are the two bands of frquencies located below and above the carrier in an AM modulated signal called? |
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Definition
| Lower and upper sidebands |
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Term
| Which sideband of an AM modulated signal is a mirror-image of the modulating signal? |
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Definition
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Term
| How does the bandwidth required to transmit an AM signal compare to that for transmitting the modulating signal by itself? |
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Definition
| The bandwidth required to transmit an AM signal is twice that of the modulating signal itself. |
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Term
| What is the predominant characteristic of SSBSC modulation? |
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Definition
| The transmitted signal is one sideband transmitted without a carrier. |
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Term
| What advantage does SSBSC have over other forms of AM? |
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Definition
| All of the power applied to the transmitter is applied to the sideband carrying intelligence. This provides a 6-to-1 power improvement. |
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Term
| What makes SSBSC more efficient? |
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Definition
| SSBSC uses a reduced bandwidth providing better power efficiency. |
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Term
| In AM, what products are present in the resultant waveform? |
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Definition
| The carrier, the upper sideband (carrier plus modulating frequency), and the lower sideband (carrier minus modulation frequency). |
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Term
| What term do we use for the additional sidebands that cause unwanted bandwidth and distortion in the transmitted AM signal? |
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Definition
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Term
| What problem is associated with all forms of AM? |
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Definition
| Susceptibility to noise interference. |
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Term
| What determines the amount of deviation of an FM carrier? |
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Definition
| The amplitude of the modulating signal. |
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Term
| How does rate of deviation compare with the frequency of the modulating signal? |
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Definition
| It is directly proportional. |
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Term
| What agency is responsible for determining the maximum amount of deviation? |
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Definition
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Term
| In PM, how is the transmitted signal modulated? |
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Definition
| The carrier's phase is caused to shift at the rate of the modulating signal. |
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Term
| What effect does a change in amplitude have on a PM signal? |
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Definition
| The amount of phase signal shift is proportional to the amplitude of the modulating signal. |
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Term
| What effect does a change in frequency have on a PM signal? |
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Definition
| The rate of phase shift is controlled by the frequency of the modulating frequency. |
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Term
| How is carrier stability maintained in a PM signal? |
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Definition
| With crystal-controlled oscillators. |
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Term
| In BPSK, what amount (degrees) of phase shift of the carrier is used to represent binary 1s and 0s? |
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Definition
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Term
| What are the advantages of bi-phase modulation? |
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Definition
| The transmitted signals are insensitive to level variations data can be transmitted at higher speeds, and data can be transmitted over smaller bandwidths. |
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Term
| What are the disadvantages of BPSK? |
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Definition
| BPSK systems require a stable transmission media to guard agains phase ambiguity, along with complex and costly multiplexing equipment. |
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Term
| What are the main advantages of QPSK over BPSK? |
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Definition
| QPSK can use the same signal bandwidth of a BPSK signal and transmit twice the amount of data, and the QPSK signal is not seriously degraded when passing through a nonlinear device. |
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Term
| How is phase ambiguity overcome when PM techniques are used? |
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Definition
| By using pilot tones as a carrier of transmitting timing pulses in the data streams along with the pilot tones. |
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Term
| How many carrier phases does quadriphase modulation have? |
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Definition
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Term
| How is information represented in DPSK? |
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Definition
| By changes in phase value from one sample to the next. |
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Term
| What is the main advantage of DPSK? |
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Definition
| It requires a less complex receiver than a basic PSK signal. |
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Term
| What are the three characteristics of a pulse train that can be varied by an information signal to produce a modulated rectangular pulse train? |
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Definition
(1) Peak voltage
(2) Period
(3) Pulse width or pulse duration |
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Term
| What determines the bandwidth of a pulse train? |
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Definition
| Only the width of the pulses determines the bandwidth of a pulse train, not the frequency. |
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Term
| What characteristic of a puls train does frequency influence? |
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Definition
| Frequency influences the number, or spacing, of the harmonics. |
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Term
| What two modulation processes are required to transmit pulse-modulated signals? |
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Definition
(1) Pulse modulation
(2) AM or FM |
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Term
| Name five pulse-modulation techniques that can be used to form composite TDM signals. |
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Definition
(1) PAM
(2) PDM
(3) PPM
(4) PCM
(5) DM |
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Term
| What is the simplest analog pulse-modulation technique? |
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Definition
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Term
| Briefly describe the PAM process. |
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Definition
| A pulse carrier is amplitude modulated to convey information. |
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Term
| What is the sampling rate of a 4-kHz voice channel? |
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Definition
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Term
| What determines the amplitude of a PAM pulse? |
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Definition
| The amplitude of the modulating signal at the point of sampling. |
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Term
| What susceptibility does PAM share with AM? |
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Definition
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Term
| By what other two names do we know PDM? |
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Definition
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Term
| What determines PDM pulse width? |
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Definition
| The amplitude of the modulating signal at the point of sampling. |
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Term
| Why is PDM less affected by noise than PAM? |
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Definition
| Noise pulses are less likely to be of the correct amplitude and time of occurrence to distort the width of the PDM pulses. |
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Term
| What disadvantage is shared by both PAM and PDM? |
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Definition
| Both are proportionately affected by any distortion in pulse width or amplitude of the modulating signal. |
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Term
| How does PPM overcome the disadvantage of distortion experienced in PAM and PDM? |
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Definition
| By maintaining pulses at a constant width and amplitude. |
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Term
| What is a disadvantage of PPM? |
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Definition
| PPM requires a larger bandwidth. |
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Term
| What determines the time position of a PPM pulse? |
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Definition
| The amplitude of the modulating signal at the time of sampling. |
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Term
| Give two reasons for converting analog signals to digital signals before transmission. |
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Definition
(1) Digital signals can be regenerated
(2) Digital signals can be readily encrypted |
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Term
| What is the principal disadvantage of converting analog signals to digital signals before transmission? |
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Definition
| Quantizing noise is produced when the digital signals are converted back to their analog form |
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Term
| Of PAM, PDM, PPM, and PCM, which technique is least affected by noise? |
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Definition
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Term
| Briefly describe the PCM process. |
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Definition
| First, the analog signal is passed through a band-limiting filter and the resulting pulses are amplitude sampled. Each pulse is assigned a binary code word corresponding to its amplitude. The resulting digital signals are then modulated using AM, FM, PSK, and so forth..., and transmitted as a series of pulses and empty intervals. |
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Term
| What is quantizing noise? |
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Definition
| Quantizing noise is the distortion produced during quantization of PAM signals where the PAM pulses are "rounded-off" to the nearest allowable assigned values differing from their true amplitude values. |
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Term
| How many code bits are required to provide 16 quantized steps? |
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Definition
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Term
| Which quantizing method produces less quantizing noise? |
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Definition
| Nonuniform quantizing produces less noise than uniform quantizing. |
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Term
| How can we increase the capability for regenerating quantized pulses? |
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Definition
| By keeping the quantized pulses at a constant duration and amplitude (encoding). |
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Term
| Explain the purpose of companding. |
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Definition
| To reduce the dynamic range of a voice signal by compressing the high-amplitude portions of the signal before transmission. |
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Term
| Why is PCM less susceptible to noise than PAM or PDM? |
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Definition
| To disturb PCM, noise must insert a pulse or obscure a pulse, not merely change its height or duration. |
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Term
| How is ADPCM different from PCM? |
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Definition
| It generates a 4-bitt word per PAM sample instead of an 8-bit word. |
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Term
| Name the two methods of multiplexing. |
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Definition
| Frequency and time division. |
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Term
| Describe the difference between the two methods of multiplexing. |
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Definition
| Frequency division multiplexing is used in the transmission of analog signals and the signals are divided among the frequency bandwidth. Time division multiplexing is used in the transmission of digital signals and the signals are allocated certain time slots along the transmission line. |
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Term
| What type of signal(s) is the T1 able to transmit? |
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Definition
| Analog, digital, and video. |
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Term
| What are some of the advantages of T1 multiplexing? |
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Definition
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Term
| What method of multiplexing does T1 use? |
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Definition
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Term
| The technology of WDM is considered a method of improving what? |
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Definition
| The efficiency of fiber through condensing, or multiplexing, the transmitted channels. |
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Term
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Definition
| In WDM, each device connected to the WDM is given a different wavelength of light or differrent color in the spectrum that allows the devices to pass together across the fiber within the same area of the light spectrum. |
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Term
| What are the WDM technologies? |
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Definition
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Term
| What does CWDM use to reduce cost? |
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Definition
| CWDM's use uncooled lasers with a relaxed tolerance of +/- 3 nm. |
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Term
| What three characteristics must the DWDM optical multiplexer have? |
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Definition
| First, it must be very stable over time and temperature; second, it needs to have a relatively flat passband or region of frequencies; and third, it must reject adjacent optical channels so that they do not interfere. |
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Term
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Definition
| A unit of information based on two symbols, states, or conditions. |
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Term
| What unit of measurement is normally used in data systems to express signaling speed for equipment? |
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Definition
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Term
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Definition
| The unit of modulation rate of the shortest unit interval. |
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Term
| Briefly explain the difference between baud and bit. |
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Definition
| Baud is an expression of time (duration) while bit carries no suggestion of time. |
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Term
| What is the difference between "overflow" and "underflow" in relation to bit count integrity? |
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Definition
| Overflow is when more bits are received than expected. Underflow is when fewer bits are received than expected. |
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Term
| What are the three terms we use to describe synchronization methods used in digital signaling? |
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Definition
(1) Synchronous
(2) Asynchronous
(3) Isochronous |
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Term
| How many synchronizing pulses are needed in synchronous operation? |
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Definition
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Term
| Briefly explain the principle of synchronous operation. |
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Definition
| In synchronous operation, the receiving device is adjusted automatically to the speed of the transmitting device by comparing the speed of the incoming signal with the time base of the receiving device. |
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Term
| What constitutes an asynchronous signal? |
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Definition
| Any signal that contains synchronizing bits within its signal stream. |
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Term
| Briefly explain the principles of asynchronous operation. |
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Definition
| In asynchronous operation, a receiving device is started with a start bit and runs only until it receives one character, then a stop bit causes it to stop and wait on the next start bit. |
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Term
| How does asynchronous synchronization affect transmission speed? |
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Definition
| It slows transmission speed. |
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Term
| What is an isochronous signal? |
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Definition
| A signal where all bits are of equal duration. |
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Term
| Of the synchronization terms synchronous, asynchronous, or isochronous, which is normally used with channel-packing systems to indicate the utilization of internal timing? |
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Definition
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Term
| Name the two actors that determine when a digital transition should occur. |
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Definition
(1) The bit rate of the signal.
(2) The signal's format. |
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Term
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Definition
| Information is contained in the level. One level is transmitted for a mark and another for a space. |
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Term
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Definition
| When two consecutive mark (1) signals occur with the same polarity. |
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Term
| How does the B8ZS signal format correct ones density problems? |
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Definition
| By intentionally inserting BPVs into the signal to break up long strings of zeros. |
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Term
| Which type of framing would be used for a T1 carrying video traffic? |
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Definition
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Term
| Which framing sequence is used for synchronization with incoming data? |
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Definition
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Term
| What are the three types of communications signals that are the functions to control and process analog calls? |
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Definition
(1) Control signals
(2) Informational signals
(3) Supervisory signals |
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Term
| What are the two methods of address signaling? |
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Definition
(1) Pulse dialing
(2) Tone dialing |
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Term
| Call waiting is what type of communication signal? |
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Definition
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Term
| What is the purpose of supervisory signaling? |
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Definition
| Monitor the status of a line or circuit to determine its state. |
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Term
| What are the two digital signaling methods to transmit supervisory signaling? |
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Definition
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Term
| How does CAS signaling convey signaling information? |
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Definition
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Term
| How does CCS convey signaling information? |
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Definition
| It uses a separate network channel to transfer supervisory signaling information in an out-of-band fashion and multiplexed with the digitized voice signals. |
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Term
| What are the three CCS signaling modes? |
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Definition
(1) Associated mode
(2) Nonassociated mode
(3) Quasi-associated mode |
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Term
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Definition
| Unintellible electrical disturbances in or to an electrical system, which may cause the desired signals carrying intelligence to be masked or distorted. |
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Term
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Definition
| A mixture of all frequencies in the spectrum of interest that, if loud enough, can completely mask the desired intelligence frequencies. |
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Term
| What is the usual circuit input impedance for a transmission line? |
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Definition
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Term
| What causes impulse noise? |
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Definition
| Disturbances that have abrupt amplitudes of short duration. |
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Term
| When is the best time to take measurements of impulse noise? |
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Definition
| During periods of peak system activity. |
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Term
| Define the term, "clocking." |
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Definition
| "The rate of running" or "to keep approximately standard time." |
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Term
| What is a station clock? What can a station clock minimize? |
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Definition
| A clock that controls some or all of the equipment in the station that require local time control; the effect of most of these impairments. |
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Term
| What are two types of station clocks? |
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Definition
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Term
| What is the master station clock? |
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Definition
| A highly stable cesium beam or GPS timing signal that is tied into the primary communications equipment. |
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Term
| How does a slave clock get its timing? |
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Definition
| It locks onto an incoming data stream from a stable source. |
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Term
| How does synchronization distinguish positions in the data bit stream? |
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Definition
| Since only 1s and 0s are transmitted, the equipment uses patterns of frame bits called framing formats. |
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Term
| What three factors can affect the line quality of a long distance transmission line? |
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Definition
| Attenuation distortions, delays, and noise. |
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Term
| How can the capacitane of a transmission line be varied? |
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Definition
| By varying the type of insulation, size of wire, and spacing between wires. |
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Term
| Define electronic attack. |
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Definition
| The component of EW involving the use of electromagnetic, directed energy, or anti-radiation weapons to attack personnel, facilities, or equipment with the intent of degrading, neutralizing, or destroying enemy combat capability. |
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Term
| What is an example of electronic attack? |
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Definition
| The deployment of high-speed anti-radiation missiles to disable an area defense radar site to allow for further penetration of our attacking forces. |
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Term
| Protecting people, facilities, and equipment from electronic is known as? |
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Definition
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Term
| What are two examples of EP for a radar system? |
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Definition
| Active decoys to draw missiles off target and the varying of pulse repetition frequency on a radar set. |
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Term
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Definition
| The means of putting a picture together for battlefield commanders to allow them to have an accurate picture of the use of electromagnetic spectrum within their area of responsiblity. |
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Term
| What are two items used to provide ES capability? |
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Definition
| Radar warning receivers and intelligence platforms. |
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Term
| State the purpose of a multimeter. |
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Definition
| It allows measurement of voltage, current, and resistance. |
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Term
| How is a multimeter connected in a circuit to measure microamperes? |
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Definition
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Term
| How is a multimeter used as a voltmeter in a circuit? |
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Definition
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Term
| When using an ohmmeter to take a resistance reading, what preliminary precaution should you take? |
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Definition
| Make sure all power is disconnected from the circuit being tested. |
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Term
| What kind of cable faults can the time domain reflectometer locate? |
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Definition
| Splices, water in the cable, split pairs, and discontinuities or faults. |
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Term
| Describe the time domain reflectometer's operating principle. |
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Definition
| It is similar to that of radar. A pulse from the time domain reflectometer is applied to a cable under test. Any impedance changes in the cable cause a portion of that voltage or energy to be reflected back to the cable input. |
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Term
| Explain how cable fault information appears on the time domain reflectometer's CRT. |
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Definition
| The CRT displays the pulse's progression from application to the cable on the left-hand side of the display to it return at the right. From the display, one can determine the distance down the cable to where the fault is and the type and severity of the fault. |
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Term
| Explain the purpose of the impedance selector buttons. |
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Definition
| Used to select the input/output impedance of the time domain reflectometer. You can select 50, 75, 95, and 125 ohm impedances. |
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Term
| Describe how you would connect a cable under test to the time domain reflectometer. |
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Definition
| Do not connect live circuit cables to the input of the time domain reflectometer. Connect the cable under test to the cable connector on the front panel of the time domain reflectometer. |
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Term
| What do deflections ("pips") indicate to the time domain reflectometer user? |
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Definition
| Upward deflections ("pips") indicate high impedance mismatches or opens and downward deflections ("pips") indicate shorts or low impedance mismatches. |
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Term
| Describe the two operating modes used by the TD-9930. |
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Definition
(1) REAL-TIME operation, reflections are amplified and displayed directly on the CRT for examination.
(2) In the AVG (AVERAGE) mode, the amplified signals are averaged to reduce noise, then stored as digital data. |
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Term
| What are the four tests and measurements performed by the optical time domain reflectometer? |
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Definition
| Cable acceptance testing; cable installation; end-to-end tests; fault location. |
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Term
| What is the power that is reflected back towards the optical source? |
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Definition
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Term
| How is the signal loss represented in on optical time domain reflectometer display? |
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Definition
| The dB drop in backscatter between the two reflections is the signal loss within the fiber. |
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Term
| What index factor is the TD-9930 already programmed to accept? |
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Definition
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Term
| What are the two major sections of a BERT set that create and receive the test pattern? |
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Definition
| The data code generator (transmitter) and code detector (receiver). |
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Term
| What type of test pattern does the data code generator produce? |
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Definition
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Term
| Name two common signal codes that are used with BERT sets. |
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Definition
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Term
| Name two framing formats used with BERT sets. |
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Definition
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Term
| What does 63,511, and 2047 in a test pattern identify? |
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Definition
| The total number of bits in the test pattern. |
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Term
| Explain the purpose of a breakout box. |
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Definition
| To monitor and access all 25 conductors of EIA RS-232 and ITU V.24 interfaces between data modems and terminals. |
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Term
| What is the purpose of the 24 miniature ON/OFF switches on a breakout box? |
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Definition
| To allow all interface conductors (except frame ground pin 1) to be interrupted individually for isolated testing and observation. |
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