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.