AC UNIT-I specially for UIT RGPV 4th semester students...

1. Analog Communication
UNIT – I
Made by: Hridesh Vishwdewa

2. Definition of Analog Signal
•An analog signal is a
continuous signal that contains
time-varying quantities.
• Unlike a digital signal, which has a discrete value at each
sampling point, an analog signal has constant fluctuations.
• The illustration in the above figure shows an analog pattern
(represented as the curve) alongside a digital pattern
(represented as the discrete lines).

3. • An analog signal can be used to measure changes in some
physical phenomena such as light, sound, pressure, or
temperature.
• For instance, an analog microphone can convert sound
waves into an analog signal.
• Even in digital devices, there is typically some analog
component that is used to take in information from the
external world, which will then get translated into digital form
(using an analog-to-digital converter).

4. Systems
• A System, is any physical set of components
that takes a signal, and produces a signal. In
terms of engineering, the input is generally some
electrical signal X, and the output is another
electrical signal (response) Y.
• However, this may not always be the case.
Consider a household thermostat, which takes
input in the form of a knob or a switch, and in
turn outputs electrical control signals for the
furnace.

5. Classification of Systems
• Continuous vs. Discrete
• Linear vs. Nonlinear
• Time Invariant vs. Time Varying
• Causal vs. Noncausal
• Stable vs. Unstable

6. Continuous vs. Discrete
• One of the most important distinctions to understand is
the difference between discrete time and continuous
time systems.
• A system in which the input signal and output signal both
have continuous domains is said to be a continuous
system. One in which the input signal and output signal
both have discrete domains is said to be a continuous
system.
• Of course, it is possible to conceive of signals that
belong to neither category, such as systems in which
sampling of a continuous time signal or reconstruction
from a discrete time signal take place.

7. Linear vs. Nonlinear
• A linear system is any system that obeys the properties
of scaling (first order homogeneity) and superposition
(additivity) further described below. A nonlinear system is
any system that does not have at least one of these
properties.
• To show that a system obeys the scaling property is to
show that

13. Block
Diagram
of Comm.
system
A: The information signal to be transmitted (Voice, music, DC to represent
rudder position in Radio Control).
B: Digitally compressed data. Analogue filtering and compression is possible
too.
C: The low power radio frequency carrier signal.
D: The modulated carrier. The carrier has been modified in proportion to the
signal to be transmitted.
E: High power signal, usually radio, but light and ultrasound are common too.
F: Attenuated signal. Energy is lost in the transmission medium.
G: Amplified signal.
H: A low power copy of the original compressed signal.
I: An exact copy of the original information signal.

14. Types Of Signals
• Continuous-Time vs. Discrete-Time
• Analog vs. Digital
• Periodic vs. Aperiodic
• Finite vs. Infinite Length
• Causal vs. Anticausal vs. Noncausal
• Even vs. Odd
• Deterministic vs. Random

15. Continuous-Time vs. Discrete-Time
• As the names suggest, this classification is determined
by whether or not the time axis isdiscrete (countable)
or continuous (Figure 1). A continuous-time signal will
contain a value for all real numbers along the time axis.
In contrast to this, a discrete-time signal, often created
by sampling a continuous signal, will only have values at
equally spaced intervals along the time axis.

16. Analog vs. Digital
• The difference between analog and digital is similar to the
difference between continuous-time and discrete-time.
However, in this case the difference involves the values of the
function.
• Analog corresponds to a continuous set of possible function
values, while digital corresponds to a discrete set of possible
function values.
• A common example of a digital signal is a binary sequence,
where the values of the function can only be one or zero.

17. Periodic vs. Aperiodic
• Periodic signals repeat with some period T, while aperiodic,
or non-periodic, signals do not (Figure 3). We can define a
periodic function through the following mathematical
expression, where t can be any number and T is a positive
constant: f(t)=f(T+t) ----Eq.(1)
• The fundamental period of our function, f(t), is the smallest
value of T that the still allows Eq(1) to be true.

18. Finite vs. Infinite Length
• As the name implies, signals can be characterized as to
whether they have a finite or infinite length set of values. Most
finite length signals are used when dealing with discrete-time
signals or a given sequence of values. Mathematically
⁢
speaking, ft is afinite-length signal if it is nonzero over a finite
⁢
interval t 1<ft< t 2 where t 1 >−∞ and t 2 <∞ . An example can
⁢
be seen in Fig.4.Similarly, an infinite-length signal, ft , is
defined as nonzero over all real numbers: ∞≤ft≤−∞ ⁢

19. Causal vs. Anticausal vs. Noncausal
• Causal signals are signals that are zero for all negative time,
while anticausal are signals that are zero for all positive
time.Noncausal signals are signals that have nonzero values in
both positive and negative time Fig.5(a-c)

20. Even vs. Odd
• An even signal is any signal f such that f (t)
= f (−t). Even signals can be easily spotted
as they are aymmetric around the vertical
axis. An odd signal, on the other hand, is a
signal f such that f (t) = − f (−t) , Fig.6
• Using the definitions of even and odd
signals, we can show that any signal can be
written as a combination of an even and
odd signal. That is, every signal has an
odd-even decomposition. To demonstrate
this, we have to look no further than a
single equation.
f (t) = ½ (f (t) + f(−t) ) + ½ ( f (t) −f
(−t))

21. Deterministic vs. Random
• A deterministic signal is a signal in which each value of the signal is fixed
and can be determined by a mathematical expression, rule, or table.
Because of this the future values of the signal can be calculated from past
values with complete confidence. On the other hand, a random signal has
a lot of uncertainty about its behavior. The future values of a random signal
cannot be accurately predicted and can usually only be guessed based on
the averages of sets of signals (Figure 8).

22. Example
• Consider the signal defined for all
real t described by -
F (t) = { sin (2πt) / t } 0t≥1t<1
•This signal is continuous time, analog,
aperiodic, infinite length, causal, neither even
nor odd, and, by definition, deterministic

23. Important Continuous Time
Signals
• Sinusoids
• Complex Exponentials
• Unit Impulses
• Unit Step

24. Sinusoids
• One of the most important elemental signal that you will deal
with is the real-valued sinusoid. In its continuous-time form, we
write the general expression as -

25. Complex Exponentials
• As important as the general sinusoid,
the complex exponential function will
become a critical part of your study of
signals and systems. Its general
continuous form is written as -
A est
• where s = σ + jω is a complex number in
terms of σ, the attenuation constant,
and ω the angular frequency.

26. Unit Impulses
• The unit impulse function, also known as the Dirac
delta function, is a signal that has infinite height and
infinitesimal width. However, because of the way it
is defined, it integrates to one.
• While this signal is useful for the understanding of
many concepts, a formal understanding of its
definition more involved. The unit impulse is
commonly denoted δ( t ).
• For now, it suffices to say that this signal is crucially
important in the study of continuous signals, as it
allows the sifting property to be used in signal
representation and signal decomposition.

27. Unit Step
• Another very basic signal is the unit-step function that
is defined as -
• The step function is a
useful tool for testing and for
defining other signals. For
example, when different
shifted versions of the step
function are multiplied by
other signals, one can select
a certain portion of the signal
and zero out the rest.

28. Transmission Media
• A transmission medium (plural transmission media) is a
material substance (solid, liquid, gas, or plasma) that can
propagate energy-waves. For example, the transmission
medium for sound received by the ears is usually air, but
solids and liquids may also act as transmission media for
sound.
• The term transmission medium also refers to a technical
device that employs the material substance to transmit or
guide waves. Thus, an optical fiber or a copper cable is a
transmission medium. Not only this bt also is able to guide
the transmission of networks.

29. A transmission medium can be classified as a:
• Linear medium, if different waves at any particular point in
the medium can be superposed;
• Bounded medium, if it is finite in extent,
otherwise unbounded medium;
• Uniform medium or homogeneous medium, if its physical
properties are unchanged at different points;
• Isotropic medium, if its physical properties are the same in
different directions.

30. Transmission Media - Guided & Unguided
• Guided Transmission Media uses a "cabling" system that
guides the data signals along a specific path. The data
signals are bound by the "cabling" system. Guided Media is
also known as Bound Media. Cabling is meant in a generic
sense in the previous sentences and is not meant to be
interpreted as copper wire cabling only.
• Unguided Transmission Media consists of a means for the
data signals to travel but nothing to guide them along a
specific path. The data signals are not bound to a cabling
media and as such are often called Unbound Media.
• There 4 basic types of Guided Media:
1. Open Wire 2.Twisted Pair 3. Coaxial Cable 4.Optical
Fiber

31. Open Wire
• Open Wire is traditionally used to describe the electrical wire strung along
power poles. There is a single wire strung between poles. No shielding or
protection from noise interference is used.
• We are going to extend the traditional definition of Open Wire to include any
data signal path without shielding or protection from noise interference.
• This can include multi-conductor cables or single wires. This media is
susceptible to a large degree of noise and interference and consequently
not acceptable for data transmission except for short distances under 20 ft.

32. Twisted Pair
• The wires in Twisted Pair cabling are twisted together in pairs. Each pair
would consist of a wire used for the +ve data signal and a wire used for the -
ve data signal.
• Any noise that appears on 1 wire of the pair would occur on the other wire.
Because the wires are opposite polarities, they are 180 degrees out of
phase (180 degrees - phasor definition of opposite polarity). When the noise
appears on both wires, it cancels or nulls itself out at the receiving end.
• Twisted Pair cables are most effectively used in systems that use a
balanced line method of transmission: polar line coding (Manchester
Encoding) as opposed to unipolar line coding (TTL logic).

33. Twisted Pair
• The degree of reduction in noise interference is determined
specifically by the number of turns per foot. Increasing the
number of turns per foot reduces the noise interference.
• To further improve noise rejection, a foil or wire braid shield is
woven around the twisted pairs.
• This "shield" can be woven around individual pairs or around a
multi-pair conductor (several pairs).

34. • Cables with a shield are called Shielded Twisted Pair and commonly
abbreviated STP. Cables without a shield are called Unshielded
Twisted Pair or UTP. Twisting the wires together results in a
characteristic impedance for the cable. A typical impedance for UTP
is 100 ohm for Ethernet 10BaseT cable.
• UTP or Unshielded Twisted Pair cable is used on Ethernet 10BaseT
and can also be used with Token Ring. It uses the RJ line of
connectors (RJ45, RJ11, etc..)
• STP or Shielded Twisted Pair is used with the traditional Token Ring
cabling or ICS - IBM Cabling System. It requires a custom
connector. IBM STP (Shielded Twisted Pair) has a characteristic
impedance of 150 ohms.

35. Coaxial Cable
• Coaxial Cable consists of 2 conductors. The inner conductor is held inside
an insulator with the other conductor woven around it providing a shield.
An insulating protective coating called a jacket covers the outer conductor.
The outer shield protects the inner conductor from outside electrical signals.
The distance between the outer conductor (shield) and inner conductor plus
the type of material used for insulating the inner conductor determine the
cable properties or impedance. Typical impedances for coaxial cables are 75
ohms for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet. The
excellent control of the impedance characteristics of the cable allow higher
data rates to be transferred than Twisted Pair cable.

36. Optical Fibre
• Optical Fibre consists of thin glass fibres that can carry information at
frequencies in the visible light spectrum and beyond. The typical optical
fibre consists of a very narrow strand of glass called the Core. Around the
Core is a concentric layer of glass called the Cladding. A typical Core
diameter is 62.5 microns (1 micron = 10-6 meters). Typically Cladding has
a diameter of 125 microns. Coating the cladding is a protective coating
consisting of plastic, it is called the Jacket.

37. Optical Fibre
• An important characteristic of Fibre Optics is Refraction. Refraction
is the characteristic of a material to either pass or reflect light. When
light passes through a medium, it "bends" as it passes from one
medium to the other. An example of this is when we look into a pond
of water.
• Optical Fibres work on the principle that the core refracts
the light and the cladding reflects the light. The core
refracts the light and guides the light along its path. The
cladding reflects any light back into the core and stops
light from escaping through it - it bounds the media!

38. Optical Fiber

39. Radio Waves
• Radio waves are a type of electromagnetic radiation with wavelengths in
the electromagnetic spectrum longer than infrared light. Radio waves have
frequencies from 300 GHz to as low as 3 kHz, and corresponding
wavelengths from 1 millimeter to 100 kilometers. Like all other
electromagnetic waves, they travel at the speed of light.
• Naturally occurring radio waves are made by lightning, or by
astronomical objects. Artificially generated radio waves are used for fixed
and mobile radio communication, broadcasting, radar and other navigation
systems, satellite communication, computer networks and innumerable
other applications

40. Micro Waves
• Microwaves are radio waves with wavelengths ranging from as long as
one meter to as short as one millimeter, or equivalently, with frequencies
between 300 MHz (0.3 GHz) and 300 GHz.
• This broad definition includes both UHF and EHF (millimeter waves), and
various sources use different boundaries.[2] In all cases, microwave
includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum,
with RF engineering often putting the lower boundary at 1 GHz (30 cm),
and the upper around 100 GHz (3 mm).

41. Infrared Transmission
• Infrared transmission refers to energy in the region of the
electromagnetic radiation spectrum at wavelengths longer than those of
visible light, but shorter than those of radio waves. Correspondingly, infrared
frequencies are higher than those of microwaves, but lower than those of
visible light.
• Scientists divide the infrared radiation (IR) spectrum into three regions.
• The wavelengths are specified in microns (symbolized µ, where 1 µ =
10-6 meter) or in nanometers (abbreviated nm, where 1 nm = 10-9 meter =
0.001 5).
• The near IR bandcontains energy in the range of wavelengths closest to the
visible, from approximately 0.750 to 1.300 5 (750 to 1300 nm).
• The intermediate IR band (also called the middle IR band) consists of
energy in the range 1.300 to 3.000 5 (1300 to 3000 nm). The far IR
band extends from 2.000 to 14.000 5 (3000 nm to 1.4000 x 104 nm).

42. Infrared is used in a variety of wireless communications,
monitoring, and control applications. Here are some
examples:
2. Home-entertainment remote-control boxes
3. Wireless (local area networks)
4. Links between notebook computers and desktop computers
5. Cordless modem
6. Intrusion detectors
7. Motion detectors
8. Fire sensors
9. Night-vision systems
10.Medical diagnostic equipment
11.Missile guidance systems
12.Geological monitoring devices

43. Bye-Bye