EST Essentials - Ch. 1: Principles of Communications

equipment that sparks

"Man-made" noise can come from __________.

equal power per octave

"Pink" noise has __________.

180 degrees

A class B amplifier conducts for how many degrees of an input sine wave?

a transmitter, a receiver, and a channel

A complete communication system must include:

discrete time signal generated by digital modulation

A digital signal is __________.

frequency domain

A display of signal amplitude versus frequency is called the __________.

one-millionth of a meter

A micron is:

noise factor

A more precise evaluation of the quality of a receiver as far as noise is concerned.

a set of sine waves

A periodic signal can always be decomposed into:

a harmonic of the 2 kHz signal

A signal is composed of a fundamental frequency of 2 kHz and another of 4 kHz. This 4 kHz signal is referred to as __________.

P2 equals P1

A signal is measured at two different points. The power is P1 at the first point and P2 at the second point. The dB is 0. This means __________.

continuous signal which represents physical measurements

An analog signal is a __________.

a sine wave of constant frequency and amplitude

An ideal sinusoidal oscillator would produce which of the following outputs?

shortwaves

Another name for signals in the HF range is __________.

530 nanometers

Approximate wavelength of green light is __________.

decreases

As frequency increases, the period __________.

analog

Continuous voice or video signals are referred to as being:

RF noise radiated by distant stars

Cosmic noise is __________.

All of the above: 1. Used for a precise frequency 2. Used for very low frequency drift (parts per million) 3. made by grinding quartz to exact dimensions

Crystal-Controlled oscillators are:

all of the above: 1. creation of harmonics of baseband frequencies; 2. baseband frequencies "mixing" with each other;; 3. shift in phase relationships between baseband frequencies

Distortion is caused by:

radio

Electrical energy at a frequency of 7,125 kHz is in what frequency range?

infrared rays

Electromagnetic waves produced primarily by heat are called __________.

EHF

For a given bandwidth signal, more channel space is available for signals in the range of __________.

half-wave symmetry

If a periodic voltage waveform is such that the waveform for the first half cycle repeats itself except with the opposite sign for the second half cycle, it is said to have __________.

odd function

If a periodic voltage waveform is symmetric about a line midway between the vertical axis and the negative horizontal axis and passing through the coordinate origin, it is said to have point, or skew, symmetry is called a or an:

even function

If a periodic voltage waveform is symmetric about the vertical axis, it is said to have axes, or mirror, symmetry and is called a/n:

not changed

If the bandwidth is tripled, the signal power is __________.

-2

If the maximum amplitude of a sine wave is 2 volts, the minimum amplitude is __________ volts.

C

If the output of a circuit should be a representation of less than one-half of the input signal, what class of operation should be used?

peak amplitude

In a frequency-domain plot, the vertical axis measures the __________.

amplitude

In a time-domain plot, the vertical axis is a measure of:

only one of the two parties can transmit at a time

In half-duplex communications:

fundamental and subharmonic waves

Indicate the false statement. Fourier analysis shows that a sawtooth wave consists of __________.

predictable in character

Indicate the false statement. From the transmitter, the signal deterioration because of noise is usually __________.

reduce the bandwidth used

Indicate the false statement. Modulation is used to __________.

antenna lengths will be approximately lambda over 4 long. λ/4

Indicate the false statement. The need for modulation can best be exemplified by the following:

Boltzmann's constant

Indicate the false statement. The square of the thermal noise voltage generated by a resistor is proportional to __________.

thermal agitation

Most internal noise comes from __________.

microvolts

Noise at the input to a receiver can be as high as several:

narrowing the bandwidth

Noise can be reduced by:

how much noise an amplifier adds to a signal

Noise figure is a measure of __________.

all of the above: 1. the sender; 2. the receiver; 3. the channel

Noise in a communication system originates in __________.

high-frequency spikes

Noise is primarily __________.

directly; inversely

Propagation time is __________ proportional to distance and __________ proportional to propagation speed.

2 pi * f

Radians per second is equal to __________.

electric and magnetic fields

Radio signals are made up of __________.

VLF to EHF

Radiowave spectrum is from __________ to __________.

noise

Random interference to transmitted signals is called __________.

transistors and diodes

Shot noise is generated in __________.

amplification

Signal attenuation can be corrected by:

pink noise

So called "1/f" noise is also called __________.

a constant radiation from the sun

Solar noise is:

VHF

Television broadcasting occurs in which ranges?

a modified Colpitts oscillator

The Clapp oscillator is __________:

a two-capacitor divider

The Colpitts VFO uses __________.

a tapped inductor

The Hartley oscillator uses __________.

multiple base band signals transmitting simultaneously would interfere with one another

The base band signal cannot usually be transmitted through space by radio because:

attenuated

The communications medium causes the signal to be __________.

period

The degree to which a cycle has been completed at any given instant is referred to as the __________.

dominates at higher frequencies

The following are characteristics of atmospheric noise, except __________.

usually between 1-600 GHz

The following are the characteristics of industrial noise, except __________.

Class C

The most efficient RF power amplifier is which class amplifier?

baseband signal

The original electrical information signal to be transmitted is called the __________.

positive alternation

The part of a sine wave that is above the voltage reference line is referred to as the __________.

greater at low frequencies

The power density of "flicker" noise is __________.

logarithmic ratio between input and output

The term "bel" is a unit measurement that expresses which of the following relationships?

waveguides

The three primary communications media are the following, except:

a mathematical ratio

The unit "decibel" is used to indicate __________.

unchanged

The value of a resistor creating thermal noise is tripled. The noise power generated is therefore __________.

the distance a wave travels in one second

The wavelength of a radio signal is __________.

frequencies of the signal, and medium

The wavelength of a signal depends on the __________.

all of the above: 1. transistors and diodes; 2. resistors; 3. copper wire

Thermal noise is generated in __________.

directly; directly

Wavelength is __________ proportional to propagation speed and __________ proportional to period.

A

What class of operation has the highest fidelity?

higher Q

What electrical characteristic makes the frequency stability of a crystal higher than that of an LC tank circuit?

it goes down

What happens to a signal's frequency as its wavelength gets longer?

it gets shorter

What happens to a signal's wavelength as its frequency increases?

prevents externally generated noise from exceeding a certain amplitude

What is a noise limiter?

an instrument that shows amplitude-versus-frequency plot

What is a spectrum analyzer?

an instrument that shows signal waveforms

What is an oscilloscope?

the signal loses strength due to the resistance of the transmission medium

What is attenuation?

noise that cannot be present in the circuit unless there is an input signal

What is correlated noise?

the signal loses strength due to the different propagation speeds of each frequency that makes up the signal

What is distortion?

an outside source such as crosstalk corrupts a signal

What is noise?

transmitting and receiving on the same frequency

What is simplex operation?

crystal-controlled oscillator, RC oscillator, and LC oscillator

What three circuits are most commonly used as frequency determining devices?

1.5 decibels (not 2 dB, 3.7 dB, nor 4.1 dB among the choices)

Which noise figure represents lowest noise?

better frequency stability

Which of the following advantages does the Colpitts oscillator have over the Armstrong and Hartley oscillators?

bandwidth

Which of the following can be determined from a frequency-domain graph of a signal?

consists of sudden burst of irregularly shaped pulses

Which of the following characterizes impulse noise?

noise power that varies inversely with frequency

Which of the following describes pink noise?

noise that is due to random variations in current flow in active devices such as tubes, transistors, semiconductor diodes, etc.

Which of the following describes shot noise?

noise that occurs only in devices where single current separates into two or more paths

Which of the following describes transistor noise?

any modification to a stream of carriers as they pass from input to output of a device produces an irregular, random variation

Which of the following describes transit-time noise?

noise that is produced by random motion of electrons in a conductor due to heat

Which of the following describes white noise?

telemetry

Which of the following is different from the other?

thermal agitation

Which of the following is not a source of external noise?

another communication signal

Which of the following is not a source of noise?

dB (decibels)

Which of the following is not an actual amount of power?

x-rays

Which of the following is not used for communications?

Crystal

Which of the following oscillators is used to provide a highly-stable output at a very precise frequency?

another communications signal

Which of the following signal is not a source of noise?

the input signal remains unchanged and the output signal is controlled by the input signal

Which of the following statements describes the relationship of input and output signals in an amplifier?

to provide signals of usable amplitude

Why are amplifiers used in electronic devices?

because the human ear can sense sounds in this range

Why do we call signals in the range 20 Hz to 20,000 Hz audio frequencies?

bel

__________ is mathematically equal to the logarithm to the base ten of the power ratio P1 over P2.