Antenna is part of the transmitter circuit in any communication system.
False
T/F
The input to source encoder can be digital or analog
true
T/F
The encryption process can be done during the decoding process
false
T/F
Super imposing the carrier signal on the message signal is called modulation
false
T/F
the antenna is used to convert electrical signals into EM waves.
true
T/F
A full duplex mode allows for communication in both directions but not at the same time
False
T/F
the telephone is an example of analog to digital communication
false
T/F
in space electrical and magnetic waves are displaced by 90 degrees
true
T/F
the number of oscillations per second is called the time period
false
T/F
the frequency of a signal is 1Hz when the time period of 1 second
true
T/F
as the frequency increases the velocity of light increases.
false
T/F
the most convenient way to express power loss and gain is in terms of decibels
true
T/F
as the current through a component increases, the noise level it produces increases.
true
T/F
a signal that repeats it self in a predictable manner is called a periodic signal
true
T/F
the size of an antenna can be reduced by using modulation.
true
T/F
modulation and demodulation can be done at the transmitter and receiver respectively
true
T/F
AM, FM, and PM fall under angle modulation techniques
false
T/F
the ratio of the carrier signal amplitude to the message signal amplitude is called as modulation index in AM.
false
T/F
AM in nature is wasteful in nature
true
T/F
an FM signal can be used to generate a PM signal
true
T/F
putting an information signal on to a carrier is called modulation.
true
false
true
T/F
a communication system may or may not include channels
true
false
false
T/F
the carrier frequency is higher than the highest base band
true
false
true
T/F
for radio signals. longer wave lengths means higher frequency
true
false
true
T/F
noise is easily removed from an analog signal by using filters
true
false
false
T/F
audio signals are in the time domain, but radio signals are in the frequency domain
true
false
false
T/F
digital systems such as computers are not affected by noise
true
false
false
T/F
every component in an electronic system generates noise
true
false
true
T/F
the hotter a component gets the more noise it generates
true
false
true
T/F
"shot" noise creates a "noise current" in an electronic device such as a transistor
true
false
true
T/F
signal - to - noise ration is more important than noise power
true
false
true
Short answer
a complete communication system must include
_______, ______, _______.
a transmitter
a receiver
a channel
Short answer
in the FM the _______ and in PM the _______ of the modulated carrier signal varies in accordance with the amplitude of the message signal
Frequency mod
Phase angular
Short answer
the modulation index in FM is the ratio of the peak deviation on the __________ frequency.
message
Short answer
radians per sec is equal to:
Short answer
when two or more signals are in a common channel, it is called:
multiplexing
Short answer
the wavelength of a radio signal is:
-or-
the distance a wave travels in one period
Short answer
noise in a communication system originates in
_____, _____, ______.
the sender
the receiver
the channel
Short answer
"man made " noise can come from?
_____ ___ _____.
equipment that sparks
Short answer
thermal noise is generated in :
____, _______, ______.
transistors and diodes
resistors
copper wire
Short answer
shot noise is generated in:
______ and ______.
transistors and diodes
Short answer
signal to noise ratio is calculated as:
signal power divided by noise power.
-or-
Fill in the blank
a radio signal's _________________ is the distance it travels in one cycle of the carrier
wavelength
Fill in the blank
in free space, radio signals travel at_______ meters per second.
Fill in the blank
the equipment used to show signals in the frequency domain is the _______
spectrum analizer
Fill in the blank
thermal noise is caused by the random motions of _______ in a conductor
electrons
Short answer
name the five elements in a block diagram of a communication system.
source
transmitter
channel
receiver
final destination
Problem Solving
the input to an amplifier has a signal to noise ration of 100 dB and an output signal to noise ratio of 80 dB. how do you determine the NF in dB?
NF = 100 dB - 80 dB
NF = 20 dB
Problem Solving
the input to an amplifier has a signal to noise ration of 100 dB and an output signal to noise ratio of 80 dB. how do you determine the NF as a ratio?
NF = 100 dB - 80 dB, NF = 20 dB
20 = 10 log_{10 }(s/n)
1.58=(s/n)
Problem Solving
What is the over all gain?
overall gain = (-9) + 12
= 3 dB
Note: because all the values are in dB they can simply be added.
Problem Solving
if the output is 200 Watts than what is the input power?
x=100.23 watts
Problem Solving
What is the output if the input is 1 watt
x = 1.99
Problem Solving
what is the formula to find the frequency of a radio signal?
what is PDM
Pulse-Duration or Width Modulation (PDM or PWM)
lecture 5
what is PPM
Pulse positon modulation
note: PPM has a similar noise performance as FM.
how does PWM work?
In Pulse Width Modulation (PWM), the width of each pulse is made directly proportional to the amplitude of the information signal.
how does PPM work?
In Pulse position modulation, constant-width pulses are used, and the position or time of occurrence of each pulse from some reference time is made directly proportional to the amplitude of the information signal.
Name the tree different type of waves.
1. PAM
2. PWM
3. PPM
What is quantization?
it is the process of converting an analog signal into a digital signal ( bits ).
what type of sampling is this and why?
ideal sampling
because the pulse width is zero.
How many leves are there for this signal and what bit type can be produce from it?
8 Levels
An 8 bit signal will be produced.
What is quantization error?
It is an error that occurs due to each point being rounded to the mid point of its correspondent zone. The more zones the smaller the errors.
what is step size in quantization?
it is the distance between each level.
A sampling has produced the following values:
-10, 8, -6, -4, 8, 5, 1, 10, 9
Determine the step size if it has 8 levels.
Step size (delta)= (the highest - the lowest) / the number of levels
=(10 - (-10)) / 8
=20/8
=2.5
What is theformula to determine the bit rate?
The bit rate of a PCM signal can be calculated form the number of bits per sample x the sampling rate
Bit rate = n_{b} * f_{s}
Calculate the bit rate.
levels L=8
bits per sample n=3
samples per sec f_{s}=3M
n_{b}=n*f_{s}
n_{b} = 9mbpM
is the antenna part of the transmitter?
NO!
What i the sampling rate for a frequency of 6MHz?
12M samples per seec
Note: the nyquis theorem states that the sampling rate should be twice the highest frequency.
TF
The rate at which information is transmitted per second is called bit rate
true
TF
Sampling transforms a discrete time signal to a continuous time signal
False
it transforms a continuous into a discrete time signal.
TF
Compression is usually done at the receiver
false
it is done at the transmitter
TF
Discretizing the amplitude levels is called quantization
true
TF
Sampling and quantization together converts an analog signal into a digital signal
True
TF
bandwidth of a digital signal is less than an analog signal
False
TF
interpolation is the reverse process of sampling at the receiver side.
true
it is "connecting the dots" received from the transmitter in order to reconstruct the signal at the receiver side.
TF
Line coding are techniques used to convert stream of bits into a signal
True
TF
A continuous signal is one that is defined at discrete intervals of time.
False
continuous signals have an infinite number of values.
TF
In ideal sampling, the width of the pulse is zero.
True
the ideal sample signal will look like a straight spike with no width
TF
The sampling rate should equal to the maximum frequency contained in the signal.
False
As per the Nyquis theorem, it should at least twice the maximum frequency.
TF
For a Low pass signal the band width is equal to the max Frequency
True
the frequency on a low pass signal begins at 0 and ends at the max frequency.
TF
As the number of levels in quatization increase the quatization error will decrease.
True
more levels mean that the signal will shift less up or down to reach the middle of the level.
TF
The number of bits required for a 128 level quantizer is 7
True
128 equals 2^7. This means that it will require 7 binary units.
TF
Assigment of non-overlapping frequency ranges to different signals is called FDM.
True
FDM stands for frequency division multiplexing
TF
TDM has high latency when compared with FDM
True
FDM stands for frequency division multiplexing
TDM stands for time division multiplexing
TF
In polar RZ encoding scheme, each symbol has a transition in the middle from high to zero or from low to zero.
True
RZ stands for return to zero
T/F
in TDM the signal uses all the bandwidth but some of the time.
False
T/F
A demultiplexer is used at the receiver side
True.
A demultiplexer separates the different signals that have been converted into one by the multiplexer.
Short answer
What is needed to calculate the sampling rate?
the maximum frequency in the signal
Short answer
What two things are needed to calculate the bit rate?
The sampling rate
The number of bits per sample
Short answer
How do you calculate the bit rate?
Sampling rate times the number of bits per sample.