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effective 7/01/2016 thru 6/29/2020

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Topic 2016-E8: Signals and Emissions


2016-E8A: AC waveforms: sine, square, sawtooth and irregular waveforms; AC measurements; average and PEP of RF signals; Fourier analysis; Analog to digital conversion: Digital to Analog conversion

2016-E8A01: What is the name of the process that shows that a square wave is made up of a sine wave plus all of its odd harmonics?

Fourier analysis

Vector analysis

Numerical analysis

Differential analysis



2016-E8A02: What type of wave has a rise time significantly faster than its fall time (or vice versa)?

A sawtooth wave

A cosine wave

A square wave

A sine wave



2016-E8A03: What type of wave does a Fourier analysis show to be made up of sine waves of a given fundamental frequency plus all of its harmonics?

A sawtooth wave

A square wave

A sine wave

A cosine wave



2016-E8A04: What is "dither" with respect to analog to digital converters?

A small amount of noise added to the input signal to allow more precise representation of a signal over time

An abnormal condition where the converter cannot settle on a value to represent the signal

An error caused by irregular quantization step size

A method of decimation by randomly skipping samples



2016-E8A05: What would be the most accurate way of measuring the RMS voltage of a complex waveform?

By measuring the heating effect in a known resistor

By using a grid dip meter

By measuring the voltage with a D'Arsonval meter

By using an absorption wave meter



2016-E8A06: What is the approximate ratio of PEP-to-average power in a typical single-sideband phone signal?

2.5 to 1

25 to 1

1 to 1

100 to 1



2016-E8A07: What determines the PEP-to-average power ratio of a single-sideband phone signal?

The characteristics of the modulating signal

The frequency of the modulating signal

The degree of carrier suppression

The amplifier gain



2016-E8A08: Why would a direct or flash conversion analog-to-digital converter be useful for a software defined radio?

Very high speed allows digitizing high frequencies

Very low power consumption decreases frequency drift

Immunity to out of sequence coding reduces spurious responses

All of these choices are correct



2016-E8A09: How many levels can an analog-to-digital converter with 8 bit resolution encode?

256

8

8 multiplied by the gain of the input amplifier

256 divided by the gain of the input amplifier



2016-E8A10: What is the purpose of a low pass filter used in conjunction with a digital-to-analog converter?

Remove harmonics from the output caused by the discrete analog levels generated

Lower the input bandwidth to increase the effective resolution

Improve accuracy by removing out of sequence codes from the input

All of these choices are correct



2016-E8A11: What type of information can be conveyed using digital waveforms?

All of these choices are correct

Human speech

Video signals

Data



2016-E8A12: What is an advantage of using digital signals instead of analog signals to convey the same information?

Digital signals can be regenerated multiple times without error

Less complex circuitry is required for digital signal generation and detection

Digital signals always occupy a narrower bandwidth

All of these choices are correct



2016-E8A13: Which of these methods is commonly used to convert analog signals to digital signals?

Sequential sampling

Harmonic regeneration

Level shifting

Phase reversal






2016-E8B: Modulation and demodulation: modulation methods; modulation index and deviation ratio; frequency and time division multiplexing; Orthogonal Frequency Division Multiplexing

2016-E8B01: What is the term for the ratio between the frequency deviation of an RF carrier wave and the modulating frequency of its corresponding FM-phone signal?

Modulation index

FM compressibility

Quieting index

Percentage of modulation



2016-E8B02: How does the modulation index of a phase-modulated emission vary with RF carrier frequency (the modulated frequency)?

It does not depend on the RF carrier frequency

It increases as the RF carrier frequency increases

It decreases as the RF carrier frequency increases

It varies with the square root of the RF carrier frequency



2016-E8B03: What is the modulation index of an FM-phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency when the modulating frequency is 1000 Hz?

3

0.3

3000

1000



2016-E8B04: What is the modulation index of an FM-phone signal having a maximum carrier deviation of plus or minus 6 kHz when modulated with a 2 kHz modulating frequency?

3

6000

2000

1/3



2016-E8B05: What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus-or-minus 5 kHz when the maximum modulation frequency is 3 kHz?

1.67

60

0.167

0.6



2016-E8B06: What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz when the maximum modulation frequency is 3.5 kHz?

2.14

0.214

0.47

47



2016-E8B07: Orthogonal Frequency Division Multiplexing is a technique used for which type of amateur communication?

High speed digital modes

Extremely low-power contacts

EME

OFDM signals are not allowed on amateur bands



2016-E8B08: What describes Orthogonal Frequency Division Multiplexing?

A digital modulation technique using subcarriers at frequencies chosen to avoid intersymbol interference

A frequency modulation technique which uses non-harmonically related frequencies

A bandwidth compression technique using Fourier transforms

A digital mode for narrow band, slow speed transmissions



2016-E8B09: What is meant by deviation ratio?

The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency

The ratio of the audio modulating frequency to the center carrier frequency

The ratio of the carrier center frequency to the audio modulating frequency

The ratio of the highest audio modulating frequency to the average audio modulating frequency



2016-E8B10: What describes frequency division multiplexing?

Two or more information streams are merged into a baseband, which then modulates the transmitter

The transmitted signal jumps from band to band at a predetermined rate

The transmitted signal is divided into packets of information

Two or more information streams are merged into a digital combiner, which then pulse position modulates the transmitter



2016-E8B11: What is digital time division multiplexing?

Two or more signals are arranged to share discrete time slots of a data transmission

Two or more data streams are assigned to discrete sub-carriers on an FM transmitter

Two or more data streams share the same channel by transmitting time of transmission as the sub-carrier

Two or more signals are quadrature modulated to increase bandwidth efficiency






2016-E8C: Digital signals: digital communication modes; information rate vs bandwidth; error correction

2016-E8C01: How is Forward Error Correction implemented?

By transmitting extra data that may be used to detect and correct transmission errors

By the receiving station repeating each block of three data characters

By transmitting a special algorithm to the receiving station along with the data characters

By varying the frequency shift of the transmitted signal according to a predefined algorithm



2016-E8C02: What is the definition of symbol rate in a digital transmission?

The rate at which the waveform of a transmitted signal changes to convey information

The number of control characters in a message packet

The duration of each bit in a message sent over the air

The number of characters carried per second by the station-to-station link



2016-E8C03: When performing phase shift keying, why is it advantageous to shift phase precisely at the zero crossing of the RF carrier?

This results in the least possible transmitted bandwidth for the particular mode

It is easier to demodulate with a conventional, non-synchronous detector

It improves carrier suppression

All of these choices are correct



2016-E8C04: What technique is used to minimize the bandwidth requirements of a PSK31 signal?

Use of sinusoidal data pulses

Zero-sum character encoding

Reed-Solomon character encoding

Use of trapezoidal data pulses



2016-E8C05: What is the necessary bandwidth of a 13-WPM international Morse code transmission?

Approximately 52 Hz

Approximately 13 Hz

Approximately 26 Hz

Approximately 104 Hz



2016-E8C06: What is the necessary bandwidth of a 170-hertz shift, 300-baud ASCII transmission?

0.5 kHz

0.1 Hz

0.3 kHz

1.0 kHz



2016-E8C07: What is the necessary bandwidth of a 4800-Hz frequency shift, 9600-baud ASCII FM transmission?

15.36 kHz

9.6 kHz

4.8 kHz

5.76 kHz



2016-E8C08: How does ARQ accomplish error correction?

If errors are detected, a retransmission is requested

Special binary codes provide automatic correction

Special polynomial codes provide automatic correction

If errors are detected, redundant data is substituted



2016-E8C09: Which is the name of a digital code where each preceding or following character changes by only one bit?

Gray code

Binary Coded Decimal Code

Extended Binary Coded Decimal Interchange Code

Excess 3 code



2016-E8C10: What is an advantage of Gray code in digital communications where symbols are transmitted as multiple bits

It facilitates error detection

It increases security

It has more possible states than simple binary

It has more resolution than simple binary



2016-E8C11: What is the relationship between symbol rate and baud?

They are the same

Baud is twice the symbol rate

Symbol rate is only used for packet-based modes

Baud is only used for RTTY






2016-E8D: Keying defects and overmodulation of digital signals; digital codes; spread spectrum

2016-E8D01: Why are received spread spectrum signals resistant to interference?

Signals not using the spread spectrum algorithm are suppressed in the receiver

The high power used by a spread spectrum transmitter keeps its signal from being easily overpowered

The receiver is always equipped with a digital blanker

If interference is detected by the receiver it will signal the transmitter to change frequencies



2016-E8D02: What spread spectrum communications technique uses a high speed binary bit stream to shift the phase of an RF carrier?

Direct sequence

Frequency hopping

Binary phase-shift keying

Phase compandored spread spectrum



2016-E8D03: How does the spread spectrum technique of frequency hopping work?

The frequency of the transmitted signal is changed very rapidly according to a particular sequence also used by the receiving station

If interference is detected by the receiver it will signal the transmitter to change frequencies

If interference is detected by the receiver it will signal the transmitter to wait until the frequency is clear

A pseudo-random binary bit stream is used to shift the phase of an RF carrier very rapidly in a particular sequence



2016-E8D04: What is the primary effect of extremely short rise or fall time on a CW signal?

The generation of key clicks

More difficult to copy

The generation of RF harmonics

Limits data speed



2016-E8D05: What is the most common method of reducing key clicks?

Increase keying waveform rise and fall times

Low-pass filters at the transmitter output

Reduce keying waveform rise and fall times

High-pass filters at the transmitter output



2016-E8D06: Which of the following indicates likely overmodulation of an AFSK signal such as PSK or MFSK?

Strong ALC action

High reflected power

Harmonics on higher bands

Rapid signal fading



2016-E8D07: What is a common cause of overmodulation of AFSK signals?

Excessive transmit audio levels

Excessive numbers of retries

Ground loops

Bit errors in the modem



2016-E8D08: What parameter might indicate that excessively high input levels are causing distortion in an AFSK signal?

Intermodulation Distortion (IMD)

Signal to noise ratio

Baud rate

Repeat Request Rate (RRR)



2016-E8D09: What is considered a good minimum IMD level for an idling PSK signal?

-30 dB

+10 dB

+15 dB

-20 dB



2016-E8D10: What are some of the differences between the Baudot digital code and ASCII?

Baudot uses 5 data bits per character, ASCII uses 7 or 8; Baudot uses 2 characters as letters/figures shift codes, ASCII has no letters/figures shift code

Baudot uses 4 data bits per character, ASCII uses 7 or 8; Baudot uses 1 character as a letters/figures shift code, ASCII has no letters/figures code

Baudot uses 6 data bits per character, ASCII uses 7 or 8; Baudot has no letters/figures shift code, ASCII uses 2 letters/figures shift codes

Baudot uses 7 data bits per character, ASCII uses 8; Baudot has no letters/figures shift code, ASCII uses 2 letters/figures shift codes



2016-E8D11: What is one advantage of using ASCII code for data communications?

It is possible to transmit both upper and lower case text

It includes built in error correction features

It contains fewer information bits per character than any other code

It uses one character as a shift code to send numeric and special characters



2016-E8D12: What is the advantage of including a parity bit with an ASCII character stream?

Some types of errors can be detected

Faster transmission rate

The signal can overpower interfering signals

Foreign language characters can be sent





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