Signal classifications

Question 1

first important classification betwwen 2 types of signals

Answer 1

analog and digital

Question 2

what is an analog signal

Answer 2

a continuous time function

Question 3

what is a digital signal

Answer 3

a signal given at discrete times (after A/D conversion)

Question 4

advantages of digital systems

Answer 4

-no sensitivity to electro-magnetic interference
-low uncertanty at relatevely low cost
-high repeatability and reproducibility
-easy to manipulate, transmit and reproduce
-flexible
-fast
-only way to store info in computer
-more robust to noise

Question 5

drawbacks of digital systems

Answer 5

we loose information and we aproximate information, if we use a small sampling time we don’t loose important info, if distance between horizontal lines is correct also the approximation doesn’t let us loose important info

Question 6

what is a logical signal

Answer 6

is the easiest kind of codification, it has just 2 discrete states: on and off.
(their origin can be both a digital or analog signal)

Question 7

which are the 2 main types of logical signal

Answer 7

trigger signal and TTL (Transistor to Transistor Logic)

Question 8

example of logical signal

Answer 8

signal of photocells, 0 if there is nothing in front of it 1 if there is something

Question 9

other important 2 categories of signal classification

Answer 9

deterministic and random

Question 10

deterministic has 2 sub categories which are

Answer 10

periodic and non periodic

Question 11

deterministic periodic signal has 2 sub categories which are

Answer 11

simple harmonic and complex harmonic

Question 12

deterministic non periodic signal has 2 sub categories which are

Answer 12

quasi periodic and transient

Question 13

random has 2 sub categories which are

Answer 13

stationary and non stationary

Question 14

random stationary has 2 sub categories which are

Answer 14

ergodic and non ergodic

Question 15

def of random signal

Answer 15

if we know the value of the signal at time t it’s not possible to forsee the value the same signal will have at the immediately next time (t+dt) or at the far future

Question 16

def of periodic signal

Answer 16

signal given in the time domain as function whose shape repeats itself at defined time lags all equal to each other

Question 17

example of single harmonic periodic deterministic signal

Answer 17

shaft vibration due to residual unbalance

Question 18

what is a deterministic, periodic, complex harmonic signal

Answer 18

is the sum of many harmonic components, it can be decomposed in a fourier series

Question 19

what is a deterministic, non periodic, quasi-periodic signal

Answer 19

in general a signal made from the sum of many harmonic components is not periodic, it is periodic only if the ratio between any frequency related to different harmonic components is a rational number, so only a foundamental frequency Tp exists.
a signal is quasi periodic if at least 1 component is not an integer multiple of this foundamental frequency

Question 20

how is the fourier spectrum of a quasi periodic signal

Answer 20

it’s discrete (energy concentrated at given frequency values), it’s similar to that of complex periodic signal

Question 21

how is the spectrum of a deterministic, non periodic, transient signal

Answer 21

cannot be discrete, just continuous

Question 22

def of random non stationary signal

Answer 22

a random process is non stationary if the mean value and the auto correlation function vary with time

Question 23

def of random weakly stationary signal

Answer 23

a random process is weakly stationary if the mean value and the correlation functiondo not vary with time.
this means the mean value is constant and the correlation is just function of the delay tau

Question 24

def of random stationary signal

Answer 24

a signal is stationary if the infinite higher order moments and the join moments are independent of time

Question 25

def of random, stationary, ergodic signal

Answer 25

bo rivedi non ho capito