E8 Signals and Emissions Flashcards by Mark Casburn

E8A01 (A)

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?

A. Fourier analysis

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E8A02 (C)

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

C. A sawtooth wave

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E8A03 (A)
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. A sawtooth wave

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E8A04 (B)

What is “dither” with respect to analog to digital converters?

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

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E8A05 (D)

What would be the most accurate way of measuring the RMS voltage of a complex waveform?

D. By measuring the heating effect in a known resistor

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E8A06 (A)

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

A. 2.5 to 1

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E8A07 (B)

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

B. The characteristics of the modulating signal

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E8A08 (C)

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

C. Very high speed allows digitizing high frequencies

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E8A09 (D)

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

D. 256

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E8A10 (C)

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

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

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E8A11 (D)

What type of information can be conveyed using digital waveforms?

A. Human speech
B. Video signals
C. Data
D. All of these choices are correct

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E8A12 (C)

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

C. Digital signals can be regenerated multiple times without error

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E8A13 (A)

Which of these methods is commonly used to convert analog signals to digital signals?

A. Sequential sampling

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E8B01 (D)
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?

D. Modulation index

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E8B02 (D)

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

D. It does not depend on the RF carrier frequency

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E8B03 (A)
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?

A. 3

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E8B04 (B)
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?

B. 3

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E8B05 (D)
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?

D. 1.67

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E8B06 (A)
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?

A. 2.14

E8B07 (A)

Orthogonal Frequency Division Multiplexing is a technique used for which type of amateur communication?

A. High speed digital modes

E8B08 (D)

What describes Orthogonal Frequency Division Multiplexing?

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

E8B09 (B)

What is meant by deviation ratio?

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

E8B10 (B)

What describes frequency division multiplexing?

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

E8B11 (B)

What is digital time division multiplexing?

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

E8C01 (C) | How is Forward Error Correction implemented?

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

E8C02 (C) | What is the definition of symbol rate in a digital transmission?

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

E8C03 (A) When performing phase shift keying, why is it advantageous to shift phase precisely at the zero crossing of the RF carrier?

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

E8C04 (C) | What technique is used to minimize the bandwidth requirements of a PSK31 signal?

C. Use of sinusoidal data pulses

E8C05 (C) | What is the necessary bandwidth of a 13-WPM international Morse code transmission?

C. Approximately 52 Hz

E8C06 (C) | What is the necessary bandwidth of a 170-hertz shift, 300-baud ASCII transmission?

C. 0.5 kHz

E8C07 (A) | What is the necessary bandwidth of a 4800-Hz frequency shift, 9600-baud ASCII FM transmission?

A. 15.36 kHz

E8C08 (D) | How does ARQ accomplish error correction?

D. If errors are detected, a retransmission is requested

E8C09 (D) | Which is the name of a digital code where each preceding or following character changes by only one bit?

D. Gray code

E8C10 (D) | What is an advantage of Gray code in digital communications where symbols are transmitted as multiple bits

D. It facilitates error detection

E8C11 (A) | What is the relationship between symbol rate and baud?

A. They are the same

E8D01 (A) | Why are received spread spectrum signals resistant to interference?

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

E8D02 (B) | What spread spectrum communications technique uses a high speed binary bit stream to shift the phase of an RF carrier?

B. Direct sequence

E8D03 (D) | How does the spread spectrum technique of frequency hopping work?

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

E8D04 (C) | What is the primary effect of extremely short rise or fall time on a CW signal?

C. The generation of key clicks

E8D05 (A) | What is the most common method of reducing key clicks?

A. Increase keying waveform rise and fall times

E8D06 (B) | Which of the following indicates likely overmodulation of an AFSK signal such as PSK or MFSK?

B. Strong ALC action

E8D07 (D) | What is a common cause of overmodulation of AFSK signals?

D. Excessive transmit audio levels

E8D08 (D) | What parameter might indicate that excessively high input levels are causing distortion in an AFSK signal?

D. Intermodulation Distortion (IMD)

E8D09 (D) | What is considered a good minimum IMD level for an idling PSK signal?

D. -30 dB

E8D10 (B) | What are some of the differences between the Baudot digital code and ASCII?

B. 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

E8D11 (C) | What is one advantage of using ASCII code for data communications?

C. It is possible to transmit both upper and lower case text

E8D12 (D) | What is the advantage of including a parity bit with an ASCII character stream?

D. Some types of errors can be detected