Communication Systems

a. equipment that sparks

"Man-made" noise can come from: a. equipment that sparks b. temperature c. static d. all of the above

b. equal power per octave

"Pink" noise has a. equal power per Hertz b. equal power per octave c. constant power d. none of the above

b. a transmitter, a receiver, and a channel

A complete communication system must include: a. a transmitter and receiver b. a transmitter, a receiver, and a channel c. a transmitter, a receiver, and a spectrum analyzer d. a multiplexer, a demultiplexer, and a channel

1.5

A microwave receiver has a noise temperature of 145 K. Find its noise figure

wavelength

A radio signal's ____________________ is the distance it travels in one cycle of the carrier

noise blanking

Disabling a receiver during a burst of atmospheric noise is called ____________________.

d. all of the above

Distortion is caused by: a. creation of harmonics of baseband frequencies b. baseband frequencies "mixing" with each other c. shift in phase relationships between baseband frequencies d. all of the above

c. Frequency-Division Multiplexing

FDM stands for: a. Fast Digital Modulation b. Frequency Domain Measurement c. Frequency-Division Multiplexing d. none of the above

solar

For satellite communications, ____________________ noise can be a serious problem.

20 dB

If you have 100 mV of signal and 10 mV of noise, both across the same 100-ohm load, what is the signal to-noise ratio in dB?

TDM

In ____________________, multiple signal streams take turns using the channel.

FDM (Frequency Division Multiplexing)

In ____________________, you split the bandwidth of a channel into sub-channels to carry multiple signals.

300 million

In free space, radio signals travel at approximately ____________________ meters per second.

Pink Noise

Light is pink when it contains more red than it does other colors, and red is at the low end of the visible spectrum. Likewise, pink noise has higher power density at lower frequencies.

Fourier

Mathematically, a spectrum is represented by a ____________________ series.

Thermal, Shot, Partition, 1/f, transit-time

Name five types of internal noise.

Source, Transmitter, Channel, Receiver, Destination

Name the five elements in a block diagram of a communications system

c. how much noise an amplifier adds to a signal

Noise Figure is a measure of: a. how much noise is in the channel b. how much noise is in the channel c. how much noise an amplifier adds to a signal d. signal-to-noise ratio in dB

d. all of the above

Noise in a communication system originates in: a. the sender b. the receiver c. the channel d. all of the above

Radians per second is equal to:

Radians per second is equal to: a. 2 pi * f b. f / 2 pi c. the phase angle d. none of the above

1901

Radio signals first were sent across the Atlantic in the year ____________________.

d. none of the above

SINAD is calculated as: a. signal voltage divided by noise voltage b. signal power divided by noise power c. first add the signal power to the noise power, then divide by noise power d. none of the above

a. transistors and diodes

Shot noise is generated in: a. transistors and diodes b. resistors c. copper wire d. none of the above

b. signal power divided by noise power

Signal-to-Noise ratio is calculated as: a. signal voltage divided by noise voltage b. signal power divided by noise power c. first add the signal power to the noise power, then divide by noise power d. none of the above

b. pink noise

So called "1/f" noise is also called: a. random noise b. pink noise c. white noise d. partition noise

50 µV

Suppose there is 30 µV from one noise source that is combined with 40 µV from another noise source. Calculate the total noise voltage.

a. Time Division Multiplexing

TDM stands for: a. Time-Division Multiplexing b. Two-level Digital Modulation c. Time Domain Measurement d. none of the above

bandwidth

The 'B' in Hartley's Law stands for ____________________.

300

The UHF band starts at ____________________ MHz.

30

The VHF band starts at ____________________ MHz.

zero

The bandwidth of an unmodulated carrier is ____________________.

d. the baseband frequency

The bandwidth required for a modulated carrier depends on: a. the carrier frequency b. the signal-to-noise ratio c. the signal-plus-noise to noise ratio d. the baseband frequency

a. approximately 3kHz

The baseband bandwidth for a voice-grade (telephone) signal is: a. approximately 3 kHz b. 20 Hz to 15,000 Hz c. at least 5 kHz d. none of the above

d. all of the above

The collection of sinusoidal frequencies present in a modulated carrier is called its: a. frequency-domain representation b. Fourier series c. spectrum d. all of the above

spectrum analyzer

The equipment used to show signals in the frequency domain is the _________________________.

base

The frequency band used to modulate the carrier is called the ____________________ band.

20 dB, NF = 100

The input to an amplifier has a signal-to-noise ratio of 100 dB and an output signal-to-noise ratio of 80 dB. Find NF, both in dB and as a ratio.

channel

The job of the carrier is to get the information through the ____________________.

greater

The more information per second you send, the ____________________ the bandwidth required.

a. Marconi

The person who sent the first radio signal across the Atlantic ocean was a. Marconi b. Bell c. Maxwell d. Hertz

c. greater at low frequencies

The power density of "flicker" noise is: a. the same at all frequencies b. greater at high frequencies c. greater at low frequencies d. the same as "white" noise

1863

The telephone was invented in the year ____________________.

d. Hertz

The transmission of radio waves was first done by: a. Marconi b. Bell c. Maxwell d. Hertz

c. the distance a wave travels in one period

The wavelength of a radio signal is: a. equal to f ÷ c b. equal to c ÷ λ c. the distance a wave travels in one period d. how far the signal can travel without distortion

c. Maxwell

Theory of radio waves was originated by a. Marconi b. Bell c. Maxwell d. Hertz

electrons

Thermal noise is caused by the random motions of ____________________ in a conductor

d. all of the above

Thermal noise is generated in: a. transistors and diodes b. resistors c. copper wire d. all of the above

5.4

Two cascaded amplifiers each have a noise figure of 5 and a gain of 10. Find the total NF for the pair.

very high

VHF stands for the ____________________ frequency band.

a. VT = sqrt(V1 × V1 + V2 × V2)

When two noise voltages, V1 and V2, are combined, the total voltage VT is: a. VT = sqrt(V1 × V1 + V2 × V2) b. VT = (V1 + V2)/2 c. VT = sqrt(V1 × V2) d. VT = V1 + V2

d. multiplexing

When two or more signals share a common channel, it is called: a. sub-channeling b. signal switching c. SINAD d. multiplexing

white noise

______________ is composed of equal amounts of light at all visible frequencies. Likewise, thermal noise has equal power density over a wide range of frequencies.