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CDC Volume 2
Volume 2
| Question | Answer |
|---|---|
| What purpose of modulation involves modulating low frequency signals for transmissionover long distances? | Ease of radiation. |
| What purpose of modulation prevents interference when sharing the same communicationspath? | Channel allocation. |
| What factor determines the spacing of the sidebands in an amplitude modulated signal? | Frequency of the modulating signal. |
| The relationship of the bandwidth required for double-sideband emitted carrier (DSBEC)AM to the bandwidth of the modulating signal of the AM bandwidth alone is | twice the modulating bandwidth. |
| The output of the oscillator in a FM modulator increases in frequency with each | positive half cycle of the modulating signal. |
| In FM, the amount of oscillator frequency change is | directly proportional to the amplitude of the modulating signal. |
| A 10 kHz modulating signal has enough peak voltage to cause a deviation of 30 kHz. What isthe modulation index? | 3. |
| What is the formula to find the modulating index? | Deviation/Frequency. |
| In PM, the carrier’s | phase is shifted at the rate of the modulating signal. |
| By using 8–PSK instead of binary phase shift keying, information capacity is increased | three times. |
| By using 16–PSK, how many bit combinations are allowed to be used? | 4 |
| What is the first step in the pulse code modulation process? | The analog signal is band-limited. |
| What part of the pulse code modulation process converts a continuous time signal into adiscrete time signal? | Sampling |
| Non-uniform quantizing and companding decreases the length of the code word from | 11 to 7 bits. |
| How does synchronous transmission reduce the overhead costs of data transmission? | Blocks many characters together for transmission. |
| When using vertical redundancy check, what significance does the amount of ones have in adata bit pattern? | Determines parity. |
| Using the longitudinal redundancy check method of error correction, what does the receivercompare with the transmitter to ensure an accurate transmission of data? | Block check character. |
| What two error detection methods, when used together, are 98 percent effective in detectingerrors? | Vertical redundancy check and longitudinal redundancy check. |
| What error detection method is used for checking a data block greater than 512 and is about99 percent effective in most applications? | Cyclic redundancy check |
| When using forward error control as a method of error correction, where does errorcorrection take place? | Receiving End |
| Which statement describes an advantage of using fiber optic cable? | Electromagnetic fields do not affect fiber optic cables. |
| Which statement describes a security feature of using fiber optic cable? | |
| What component of a fiber optic cable provides the reflective surface that allows light topropagate? | Cladding |
| What type of buffer allows the fiber optic cable to be twisted or pulled with little stress onthe fiber? | Loose tube. |
| Most fiber optic links use infrared light that has a frequency range of | 750 to 1500 nm. |
| When considering light wave propagation, the normal is an imaginary line perpendicular tothe interface of two materials. The angle between the normal in the first material and the ray thatis bounced back in the first material is called the | angle of reflection. |
| Propagation of light as seen by Snell’s law is known as | total internal reflection. |
| What logarithmic expression do we use to specify the ratio of power loss in fiber opticcables? | dB/km. |
| What results from the imperfections in an optical fiber’s basic structure? | Scattering |
| The most useful way to classify fiber optic cable is by | refractive index profile and number of modes. |
| What type of fiber is the least efficient, with the highest dispersion and has a core diameterof 30μm to over 800μm? | Multimode step-index fiber. |
| What type of fiber has a core diameter of 50–125 micrometers (μm) and consists ofnumerous concentric layers of glass, something like the annular rings of a tree configured toreduce dispersion? | Multimode graded-index fiber. |
| Which analog multimeter control compensates for the voltage of the internal batteries whencalibrating for resistance measurements? | Zero ohms control. |
| When you make a resistance measurement, how do you electrically isolate a resistor fromthe circuit? | Disconnect one side of the resistor. |
| How do you place multimeter test leads in a circuit to measure voltage? | Parallel. |
| In which type of circuit would you measure the AC component of an output voltage whereboth AC and DC voltage levels exist? | Amplifier. |
| Which feature of the Fluke 8025A multimeter do you use to select various measurementfunctions? | Rotary switch. |
| Which part of the Fluke 8025A’s display section indicates the absolute value of the input? | Analog bar graph. |
| Which feature of the Fluke 8025A locks the measurement into the display for viewing andautomatically updates the display when you take a new measurement? | Touch-hold push button. |
| When you use the Fluke 8025A, which voltage range do you select to measure 50 volts DC? | Volts DC. |
| Which current range on the Fluke 8025A do you select to measure 250 milliamps AC? | Milliamps/amp AC. |
| Low-insulation resistance between conductors can cause | high-attenuation, crosstalk, and noise |
| With what values do we measure insulation resistance? | Ohms or megohms |
| Insulation resistance increases if | c. thickness of the insulating material increases. |
| When using the AN/PSM–2 megger, how do you know you are applying the correctregulated output voltage? | d. Turn the hand-crank at a rate to keep the indicator lights at a steady glow |
| What type of megohmmeter do you use on paper insulated conductor cable? | 500 volt. |
| How are voltage, time, and depth represented on the oscilloscope display? | Voltage = vertical axis, time = horizontal axis, and depth = intensity |
| Which mode of triggering an oscilloscope causes a trace to be drawn on the screen at alltimes, whether there is an input signal or not? | Auto |
| Which oscilloscope probe is essentially just a shielded piece of wire? | Passive 1:1 probe |
| Which probe lets you use the oscilloscope to measure higher voltage levels, raises the inputimpedance, does not require a bias voltage, and attenuates noise? | Passive divider, 10:1 probe |
| Which probe does not need to actually make contact with the circuit under test? | Current probe. |
| What digital storage oscilloscope circuit compensates for high sampling rates of highfrequencysignals? | Charged coupled device |
| Sampled data points are stored in the memory of a digital storage oscilloscope as | waveform points |
| What area of a digital storage oscilloscope takes digitized samples and performs numerousmanipulations on the data including measuring rise and fall times, periods, time intervals, andmath computations? | Microprocessors |
| What type of sampling does a digital storage oscilloscope normally use on single-shot orseldom-occurring signals? | Real-time |
| Which are the three types of digital storage oscilloscope acquisition modes, and which is thestandard operating mode? | Sample, peak detect, averaging; sample |
| 222) Which digital storage oscilloscope button controls all waveforms displayed in the STOREmode? | CURSORS control |
| In acquiring a 4K record length on a digital storage oscilloscope, how many samples canyou view at one time? | 1,000 |
| In the internal clock generator section of a typical bit error rate test set, what generates thebasic clock that provides all clock phases, and is periodically frequency calibrated by a crystalcontrolled oscillator in the automatic calibration section | VCO |
| Which pattern simulator section of a bit error rate test set controls the clock selector andselects either the external clock or the internal clock for processing? | Data/clock select encoder |
| 223) What pattern simulator section of the bit error rate test set accepts a 48-bit parallel word andgenerates a serial pattern? | 48-bit transmitter only. |
| What pattern simulator section of the bit error rate test set converts the NRZ-L data into thedesired coding, such as NRZ-M? | Code converter |
| What pattern synchronizer and error counter section of the bit error rate test set internallygenerates its own pattern to compare with the received data from the data/clock receivers? | PRN pattern synchronizer/comparator. |
| Which is the primary means of measuring the quality of transmitted digital information, andhow is this means derived? | Bit error rate (BER), the ratio of the number of bits in error to total number of bits transmitted |
| What is the first step in the basic bit error rate testing procedure? | A known bit pattern, usually pseudo-random, is generated at the sending end of the datachannel or equipment under test and is transmitted through the channel. |
| During a basic bit error rate testing procedure, an error signal is generated when | any bit in the received signal is not the same as the generated bit. |
| Which of these data circuit speeds would normally use the shorter generated bit error rate(BER) test pattern lengths, and what is data circuit bit rate? | Low to intermediate, 1200 to 9600 bps |
| Which of these bit rates do you use for a bit error rate test on a 64 Kbps data circuit? | 64 Kbps |
| On the bit error rate test set, the 25-pin connectors are designed to operate with datamodems to | simplify connection of test equipment to the modem under test and to carry the necessarysignaling and handshake signals for modem operations. |
| What is the frequency range of an audio signal generator? | 20 Hz to 20 kHz |
| Which one of these is not an application of a radio frequency generator? | Aligning galvanometers |
| A radio frequency generator is used to | Align telemetry receivers |
| What is the variable voltage range of signals output from the HP 3325Bsynthesizer/function generator? | 1 mV to 10 V peak-to-peak |
| The output of the HP 3325B function generator may generate only DC voltages, to amaximum of | ±5 V |
| In using the phase modulation controls of the HP 3325B function generator, an input of a ±5V peak would result in what approximate phase deviation? | ±425° per volt for square wave. |
| The 10:1 power ratio represented by 1 bel can also be represented by how many decibels(dB)? | 10 dB |
| A power reading that uses the abbreviation dBm indicates the | ratio of decibels relative to a 1-milliwatt standard. |
| The measurable frequency and power ranges of the HP 436A power meter are determinedby the | power sensor. |
| During what operation is the radio frequency blanking output used on the HP 436A powermeter? | During the automatic zeroing operation. |
| Which measurements is not made with a spectrum analyzer? | Peak-peak voltage. |
| Which measurement do you make with a spectrum analyzer? | Subcarrier oscillator outputs. |
| Which electronic counter measurement represents the average bit-to-bit time of an inputsignal? | Period. |
| Which electronic counter measurement counts the number of bits in a pulse train? | Totalize |
| Which are the correct four classes of electronic counters? | Frequency counters, universal counters, microwave counters, and reciprocal counters. |
| What principle does the time domain reflectometer use to test cables? | Radar |
| Which push-button(s) would you select to get 125Ω impedance on the time domainreflectometer? | 50Ω and 75Ω. |
| What type of deflection return on the TDR CRT would indicate a cable “short?” | Downward deflections “pip.” |
| While using a time domain reflectometer (TDR), what cable fault causes delays in pulses ofpropagation velocity making accurate measurements difficult? | Moisture in cables. |
| What do we call the power that is reflected back to an optical source in the time domainreflectometer? | Backscatter. |
| How is the signal loss represented in an optical time domain reflectometer display? | Decibels. |
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