Unit-8sietkece.com/wp-content/uploads/2018/08/ACS-unit-I-NOTES.doc · Web viewInformation is a word or group of words with certain meaning. Information is central to communication

Unit-I

Amplitude Modulation & Demodulation

RADIO FREQUENCY (RF) SPECTRUM:

Name of the Band Frequency Range Channel Application

ELF 3-30Hz Air and copper cables Telephone, telegraph

SLF 30-300Hz ” ”

ULF 300-3000Hz ” ”

VLF 3-30KHz Air, water, copper cables. Navigation, SONAR

LF 30-300KHz

Air, water and copper

cables

Aeronautical, Radio

Teletype, ground wave

comm..

MF 300-3000KHzAir, copper cables AM Broadcasting,

Ground wave Comm.

HF 3-30MHzAir, copper and co-axial

cables.

HF Comm., Citizen’s

Band, ionosphere comm..

VHF 30-300MHzAir, free space, co-axial

cable

TV Broad-casting, FM,

Point-point Comm.

UHF 300-3000MHzAir, space, waveguide. TV, mobile telephones,

satellite comm..

SHF 3-30GHz

Air, space, waveguide. Satellite comm., Wireless

LAN, Ultra wide-band

Comm., MAN.

EHF 30-300GHzOptical fiber Mostly at experimental

Stage.

Analog Communications 1 Dept. of ECE, SIETK, PUTTUR

SOME FAMILIAR FREQUENCY BANDS:

1. Communication:

Answer:-

Communication is the process of establishing a link/connection between two points (transmitter & receiver), for information exchange, via a channel.

(Or)

Simply we can define communication as a process of conveying/exchanging information.

Examples: Line telephony, radio and T.V. broad casting, radar communication, mobile communication, speech communication etc.

Elements of communication system:

In any communication system there are three essential elements. They are

1. Transmitter,2. Transmission channel, and3. Receiver


Fig.1. Basic Block diagram of Communication system

The above figure shows the block diagram of Communication system.

Information source:

1. Information is a word or group of words with certain meaning. Information is central to communication system.

2. Message is the physical form of information; message is of 2 types (analog and digital). Various types of messages are in the form of words, symbols, code, sound signal etc.

3. Signal is defined as a function of two or more variables which conveys information on the physical phenomenon of nature.

The function of information source is to generate/produce the required message which has to be transmitted.

Input Transducer:

Transducer is device used to convert one form of energy into another form. The message from the source may not be an electrical signal; an input transducer is used to convert the message signal in to electrical signal.

Example: A microphone converts message signal which is in the form of sound waves into electrical form.

Transmitter:

Transmitter process the input signal to produce another signal which is suitable for transmission over the channel. The main functions of transmitter involve modulation/coding. In long distance communication, signal amplification is needed before modulation. In modulation a low frequency signal is superimposed on a high frequency signal.

Transmission channel:


Channel refers to a medium through which the message signal travels from transmitter to receiver. The channel may be an optical fiber, co-axial cable, satellite channel/mobile radio channel etc.

As the transmitted signal propagates over the channel, it is distorted due to the physical characteristics of the channel. Moreover, noise and interference (originating from other sources) contaminates the channel output. So at the receiver we are going to receive corrupted version of our message signal.

Noise is an unwanted form of energy which tends to interfere with the transmission and reception of signals in any communication system. Noise cannot be removed completely but we can reduce noise by using some filtering techniques.

Output Transducer:

Transducer is device used to convert one form of energy into another form. An Output transducer is used to convert the electrical signal in to message signal.

Example: A loud-speaker converts electrical signal back to sound signal.

Receiver:

The main function of the receiver is to operate on the received signal, in-order to reconstruct a recognizable form of the message signal and deliver it to the destination. The role of receiver is thus the reverse process of transmitter.

Limitations of communication system:

In any communication system a designer will face two major problems

1. Technical 2. Physical

Technical Limitations includes hardware availability, economic factors, and federal regulations and so on.

Physical Limitations of information transmission is of two types’ bandwidth and noise.

Bandwidth (BW):

The concept of bandwidth applies to both signal and system as a measure of speed. BW is defined as a range/band of frequencies required for a particular transmission. Communication under real-time requires sufficient transmission BW to accommodate a signal; otherwise, sever distortions will occur.


For example, Transmission of a TV signal needs several MHz BW, while a voice signal can fit in to a few KHz BW.

Noise:

It is an unwanted form of energy which tends to interfere with the transmission and reception of signals in any communication system. Noise cannot be removed completely but we can reduce noise by using some filtering techniques.

Thermal noise is common in any communication system, because of random motion of charged particles such as electrons generates random currents/voltages.

S/N is the measure of noise relative to the message signal. If S/N is so small, then noise degrades the performance of communication system.

Taking both the limitations in account Shannon stated that the rate of information transmission cannot exceed the channel capacity (C).

i.e., C = B log (1 + S/N)

The performance of any communication system is defined in terms of fidelity and accuracy.

Fidelity refers to efficient transmission of message in analog communications. It is defined as the ability of a receiver to reproduce the frequency components of original message signal.

Accuracy refers to transmission of symbols (i.e. digital communications). It is defined as the ability of a receiver to reproduce the symbols with a less error probability.

2. Modulation & Need for modulation:

Answer:-

Modulation is defined as the process of changing the characteristics of a high frequency carrier signal according to message signal with respect to time. The device used for modulation purpose is called as modulator.

Need for modulation:

Modulation serves several purposes in communications system as discussed below:

1. Modulation for efficient Radiation/Transmission: Incase of, space propagation we require antennas to transmit/receive information, for efficient transmission of


message, the length of antenna must be 1/10th of wavelength (i.e., ) {most

preferably it is }.

For example, in AM broadcast systems the maximum audio frequency is 5 kHz, if we want to transmit this signal without modulation, then the height of antenna must be

Obviously, it is impossible to construct and install an antenna of such height. This height can be reduced if we go for modulation. If the audio frequency is translated to 3 MHz, the antenna height required would be

This antenna height may be achieved practically.

2. Modulation for reduction of noise: Interference can be reduced by transmitting a modulated signal instead of message signal directly. For example in FM broadcasting, there are several broadcasting stations and the frequency of message signal will be in the range of 20 Hz–20 kHz, if there is no modulation, all the stations transmits the signals in the range 20 Hz–20 kHz. Due to this transmission over the same range, all the programs from different stations will get mixed up.

In order to overcome this problem, it is necessary to translate/shift the frequencies to different portions of Electro-Magnetic (EM) spectrum.

3. Modulation for frequency assignment: When we tune a radio/TV set, we are selecting one signal from many signals received at that time. This is possible only if the signals from different stations have different frequencies.

4. Modulation for multiplexing: Multiplexing is the process of combining several signals for simultaneous transmission over a single channel.

Frequency Division Multiplexing (FDM) uses Continuous Wave (CW) modulation to put each signal on a different carrier frequency and a bank of filters will separate them at the destination.

Types of Modulation:


Modulation is basically of two types, which is show in the following flow-graph.

In continuous wave modulation the carrier signal is continuous with respect to time.

Amplitude Modulation is defined as the process of changing the amplitude of carrier signal according to message signal with respect to time. In this case frequency and phase of the modulated signal remains same as the carrier signal.

Frequency Modulation is defined as the process of changing the frequency of carrier signal according to message signal with respect to time. In this case amplitude and phase of the modulated signal remains same as the carrier signal.

Phase Modulation is defined as the process of changing the phase of carrier signal according to message signal with respect to time. In this case frequency and amplitude of the modulated signal remains same as the carrier signal.

Fig.3 Continuous wave modulation.

In Pulse train modulation the carrier signal is a pulse train (digital form).

Pulse Amplitude Modulation is defined as the process of changing the amplitude of carrier signal according to message signal with respect to time. In this case pulse width and pulse position of the modulated signal remains same as the carrier signal.


Pulse Width Modulation is defined as the process of changing the frequency of carrier signal according to message signal with respect to time. In this case amplitude and pulse position of the modulated signal remains same as the carrier signal.

Pulse Position Modulation is defined as the process of changing the phase of carrier signal according to message signal with respect to time. In this case amplitude and pulse width of the modulated signal remains same as the carrier signal.

Fig.4 Pulse train modulation

3. Coding:

Coding is a symbol-processing technique to improve the performance of a communication system when the information is in digital form.

Source Encoder:

The symbols produced by source are given to the source encoder to convert them in to digital form (i.e., binary sequence of 1’s and 0’s). Each binary ‘1’ and ‘0’ is known

Fig. 5. Block diagram of digital communication system

as a bit. The group of bits is called a codeword. The source encoder assigns a unique codeword to each symbol.

Source encoder can generate 2k possible code-words made up of k bits, so we need bits per codeword to encode M symbols.


If source generates r symbols per second, binary code will have bits per second and the transmission BW increases by k times.

Source Decoder:

It converts an encoded sequence back to original message with few errors caused by transmission contaminations.

Channel Encoder:

In order to remove the errors caused by noise and interference in the channel, channel encoder adds some extra bits called redundant bits to the input sequence. Also, these redundant bits are added with defined logic. Parity coding comes under channel coding technique.

Channel Decoder: Channel decoder is used to perform the reverse process of channel encoder, i.e. it removes the redundant bits for the received message to get the original message.

BAND-PASS SIGNALS AND SYSTEMS:

The effective communication for long distances transmission usually needs high frequency signals. This can be achieved by applying frequency translation property of Fourier Transforms to our message signal.

Band-pass Signals and Systems:

The effective communication for long distances transmission usually needs high frequency signals. This can be achieved by applying frequency translation property of Fourier Transforms to our message signal.

Frequency Shifting Property:

If ,

Then,


Fig. 1 Frequency shifting property

Band-Pass Signals:

Let is a real signal and is the spectrum of .

Fig. 2 Bandpass System

The spectrum exhibits Hermitian symmetry, because is real, but is not

necessarily symmetrical with respect to .

Using the frequency shifting property bandpass signal is defined as

(1)

Equation (1) says that the spectral contents outside the bandwidth of 2 are zero.

Bandpass Transmission:

Bandpass transmission is normally used at high frequencies and for long distance communication.


If modulated signal is transmitted over the channel then it is called as bandpass/passband transmission.

All TV and satellite transmission is of bandpass type.

The bandpass transmission can be both analog and digital. If the digital signal modulates the carrier then it is called digital bandpass transmission.

Analog Message Convention:

For the ease of studying modulation methods, we consider an arbitrary function , which is a sample from the ensemble of possible messages produced from information source.

The conditions that must possess are as follows:

Reasonable bandwidth

Magnitude of must be less than or equal to one (‘1’), i.e., (2)

The above condition puts an upper limit to average power i.e., (3)

In case of sinusoidal/tone modulation, the message signal is given as

(4)

Where

For multi-tone modulation, (5)

With to satisfy equation (2).

Amplitude Modulation (AM):

“AM is the process in which the amplitude of carrier signal is changed according to instantaneous values (amplitude) of message signal”

Let us consider a sinusoidal carrier


Where

Let be the message/baseband signal,

Then generalized equation for AM is given as

(1)

(2)

Where

Equation (1) describes the time domain behavior of AM wave. In equation (2) is

called “Envelope” of AM wave, and it consists of our message signal . Hence, the message signal can be recovered from AM wave by detecting the envelope.

Fig. 3 Amplitude modulation


1. The carrier is a fixed frequency signal having frequency . The

modulating/baseband signal contains information to be transmitted; this information is superimposed on the carrier signal in the form of amplitude variations. This means that the information to be transmitted is now, contained in the amplitude variations of carrier signal. This is shown in figure 3.

2. In the process of amplitude modulation, the frequency and phase of the carrier remains constant, whereas amplitude varies according to the message signal.

Spectrum of AM wave:

If is message signal and carrier is given by the expression

Then the equation of AM wave will be

The above equation describes the time domain behavior of AM signal. If we want to know the frequency components of the signal we need to find the spectrum (which is calculated using Fourier transform)

Let is the Fourier transform of , denotes Fourier transform of and

denotes Fourier transform of .

Let the message signal be band-limited to the interval as shown in figure 4.

So, the range of message signal is to , i.e., it includes the negative frequencies

.practically there is no meaning of negative frequencies. In fact it is used or mathematical convenience.

We know that Fourier transform of cosine signal consists of two impulses at

and , which is given as

.

Now the AM wave is given as (3)

To find Fourier Transform of :


First convert in to exponential form as

Then using frequency shifting property take Fourier transform for .

If

Then

And (4)

So can be written as

Now, F.T of

Now,

(5)


Fig. 4 Frequency Domain representation of AM

For positive frequencies, a portion of the spectrum of AM is lying above carrier frequency

. This band of frequency which is lying outside the carri8er frequency is the upper

sideband (USB) whereas the symmetrical portion below carrier frequency is known as the lower sideband (LSB). For negative frequencies the USB is represented by the

portion of spectrum below carrier frequency and the LSB by symmetrical portion

above . We generally keep > which ensures that the two sidebands do not overlap each other.

Modulation Index:

In AM system the modulation index is defined as the amount of amplitude of carrier is changed according to message signal. Or ratio of amplitude of message signal to amplitude of carrier signal

i.e. (6)

For our case ,

Where denotes maximum amplitude of message signal. The modulation index is also known as depth of modulation, degree of modulation. The percentage modulation is given as

So, we can write AM equation as .

Over modulation:

We know that modulation index is

Where Ac is amplitude of carrier signal, the message signal will be preserved in envelope of AM only if


i.e. modulation index is less than or equal to unity.

On the other hand, if or percentage modulation is greater than 100, the baseband signal is not preserved in the envelope of AM signal. In this case we may get distorted version of our message signal from the envelope. This type of distortion is

called envelope distortion and AM signal with is called over-modulated signal, which is shown in the following figure 5.

Fig. 5(a) AM signal for


Fig. 5(b) AM signal for

Single Tone Amplitude Modulation (AM)

Till now we discussed that the message signal is a random signal which contains many number of frequencies. But here, single tone refers to single frequency i.e. we are going to modulate the carrier signal by a single frequency signal (for example sinusoidal signals).

Consider message signal as which contains a single frequency and the

carrier be

We know that general equation for AM is

Now for becomes

(8)

The above equation gives the AM signal with

Carrier frequency having amplitude Ac

Upper side band having amplitude

Lower side band having amplitude

Using these frequency components the spectrum of single tone AM is drawn as


Fig. 6 Spectrum of Single Tone AM

Power Content in AM

We know the general form of AM as

From the above equation it is clear that the amplitude of carrier after modulation is same as amplitude of carrier before modulation (i.e. Ac) and after modulation the AM signals contains two side bands in addition to carrier, so the power in AM signal is larger than the power of carrier signal

Let be the total power in AM signal, be the carrier power and be sideband power.

Carrier Power:-

RMS value of

Since our AM signal is bandpass signal we will use bandpass filters in order to avoid unwanted frequencies, so the harmonics can be neglected from the above equation


This is carrier power.

Sideband Power:-

is the RMS value of

Since our AM signal is bandpass signal we will use bandpass filters in order to avoid unwanted frequencies, so the harmonics can be neglected from the above equation

The power carried by upper and lower sidebands is given as

Therefore, the total power carried by AM wave given as


Transmission Efficiency of AM signal

We know that the total power carried by AM wave is

Out of this total power , the useful message power is carried by the sidebands, i.e. .

The large carrier power is wasted, because it doesn’t carry any information. This carrier power is transmitted along with the sideband power for the convenient

transmission and detection only. Hence only is the useful power, this is expressed in terms of transmission efficiency .

Hence the transmission efficiency of AM wave may be defined as the percentage of total power contributed by sidebands

i.e.

This is transmission efficiency.

Power Content in Single Tone AM

We know that the message in single tone AM is


Also, the carrier power is mean square value of

i.e.

And the sideband power is

Therefore, the total power carried by AM wave given as

But

This is power content in Single tone AM

Current Calculation for Single Tone AM

Let be the carrier current, be the total modulated current of an AM transmitter. Let R be the antenna resistance through which the current flows.


We know that the total power content in a single tone AM is

From the above equation, we can deduce the current as

Power Content in Multi-Tone AM

A multi-tone AM is a type of modulation where the modulating signal consists of more than one frequency.

Let us consider message signal as and carrier as

. We know that the AM wave is given as . This will be changed as

But

Now the power relation for the above AM signal can be calculated as


Where is the total net modulation index, which is given as

DSB-SC Signals:

The equation of AM in simplest form i.e. single tone modulation is expressed as

From this equation it is clear that the carrier component remains constant in amplitude and frequency. This means that the carrier of AM wave does not convey any information. We know that from power calculation of single tone AM, the ratio of total power to

carrier power is , is modulation index. Thus for 100% modulation about 67% percent of the total power is required for transmitting the carrier which does not carry any information. Hence, the carrier is suppressed from the AM wave and in this way a saving of two-third of power will be achieved at 100% modulation depth. This type of suppression of carrier does not affect the sideband signal. The resulting signal obtained by suppressing the carrier for AM wave is called as Double Sideband Suppressed Carrier (DSB-SC) system.

Thus, in this system there is no carrier signal only sidebands are present.

i.e. ;


We know from frequency shifting property

If ,

Then

And

So can be written as

Now, F.T of

Fig. 7 DSB-SC Signals and Spectrum

The above figure shows the time domain and frequency domain representation of DSB-SC.


It is obvious that from the figure 7, that the DSB-Sc signals exhibits phase-reversal at zero crossings. Because of this the envelope of DSB-SC signal is different from the message signal.

Also the frequencies at are missing which means that the carrier term is suppressed in the spectrum and only two sideband terms are left. Therefore, it is called DSB-SC system.

The bandwidth of DSB-SC is given as = . Hence the bandwidth of DSB-SC and AM are same.

Generation of AM Signals

Square Law Modulator: This modulator makes use of non-linear current-voltage characteristics of diode. This method is suited at low voltage levels because of the fact that current-voltage characteristics of a diode is highly non linear particularly in low voltage region.

Figure shows the circuit of square law modulator, it may be observed from the figure that carrier and modulating signals are applied across the diode. A dc battery is connected across the diode to get a fixed operating point (i.e. either forward bias or reverse bias operation). The working of this circuit is explained by considering the fact

that the diode will obey the square law ( ) if the diode is operated in a fixed operating point (i.e. either forward bias or reverse bias operation).

So we can express output across the diode ( ) as . And one more specialty of this circuit is the usage of double-tuned circuit which acts a bandpass filter for this

application, i.e. the frequency is tuned to (i.e. carrier frequency). So this tuned circuit

will remove the frequencies outside . This is assumed to be greater than three times of the frequency of the message signal, such that it will allow only carrier frequency along with sideband frequencies.


Non-Linear Device

cAcos t

x( t )

1V 2V

~~

Mathematical Analysis:

Let us consider that carrier voltage is expressed as , where is carrier frequency.

Let the modulating voltage be expressed as with as modulating frequency.

The total input voltage across the diode is given as

Because of non-linear relationship the output voltage at across the diode is given as

Where a, b are constants

By placing we will get as

Since we are using tuned circuit as band-pass filter, we can eliminate 1st, 4th and 5th

terms

So we can write as

,

Where is a constant

,

Hence AM signal is generated using Square law modulator.

Where .Analog Communications 26 Dept. of ECE, SIETK, PUTTUR

Switching modulator:

The below figure shows the Switching modulator, in this arrangement it is assumed that the carrier wave c(t) applied to diode is very large. We assume that the diode acts as an ideal switch, i.e. the impedance will be zero when it is forward biased and it is infinite in reverse bias condition.

i.e. when ,the output is equal to input and when , there is no output i.e. =0.

So for an input voltage given by

where , the resulting load voltage is

That is, the load voltage varies periodically between the values and zero at rate equal to carrier frequency.

We can express the above equation as


x( t ) ~

cAcos t

~1V 2VR

Where is a periodic pulse train of period . Representing this by its

Fourier series we have .

Therefore is given as

This is desired AM equation, obtained by neglecting the higher order harmonics.

Generation of DSB-SC Signals

A double-sideband suppressed carrier modulated wave consists of the product of message signal and carrier signal.

We can generate this by using product modulators. Balanced and Ring modulator are two forms of product modulators we are going to discuss.

Balanced Modulator:

We know that a non-linear device may be used to produce a baseband signal along with carrier signal (square law modulator). But, a DSB-SC contains only two sidebands. Thus if two non linear devices are connected in balanced mode so as to suppress carrier of each other, then only sidebands are left.

Therefore, a balanced modulator can be defined as a circuit in which two non-linear devices are connected in a balanced mode to produce a DSB-SC signal.

The above scheme shows a balanced modulator consists of two AM modulators. A message signal x(t) is applied to one of the modulators and phase shift version of message signal (i.e. –x(t) ) is applied to another modulator. One more input to both the


AM Modulator

AM Modulator

x( t )

x( t )

cAcos t

cAcos t

1s ( t )

2s ( t )

s( t )

modulators is a locally generated carrier signal . Then the output of both the modulators will be summed up using a summer, producing DSB-SC wave.

Mathematical Analysis:

Let carrier be and message signal be x(t)

Then

And

Now,

Ring Modulator:

It is considered as one of the most useful product modulators, which is well suited for the generation of DSB-SC wave. The schematic diagram of Ring modulator is shown in the following figure.

The four diodes are connected in the form of a ring, hence the Ring modulator. These diodes are controlled by a square wave carrier c(t) of frequency fc , which is applied by means of two center tapped transformers. Assume diodes are ideal and the transformers are perfectly balanced.

Positive Half Cycle


c( t )

x( t ) DSB SC

For the positive half cycle of carrier wave, the outer diodes D1, D2 are switched on, whereas the inner diodes are switched off, because of infinite impedance. So the modulator multiplies the message signal with the carrier.

Negative Half Cycle

For the negative half cycle the situation becomes reverse to that of positive half cycle, the modulator will multiply the message signal with carrier with opposite phase. Thus, the ring modulator, in its ideal form, is a product modulator for a square wave carrier.

The square wave carrier c(t) can be represented by a Fourier series as follows

The ring modulator output is thus given as

=

=

By neglecting the higher harmonic frequencies s(t) can be given as

From the above equation it is clear that s(t) contain only sidebands, which called as double sideband suppressed carrier (DSB-SC).

Linear Continuous Wave Modulation Techniques

Multiplexing Techniques:

Multiplexing is a technique in which several message signals are combined into a composite signal for transmission over a common channel. In order to transmit a number of these signals over the same channel, the signals must be kept apart so that they do not interfere with each other, and hence they can be separated easily at the receiver end.

Basically multiplexing is of two types as given below:

1. Frequency Division Multiplexing (FDM)Analog Communications 30 Dept. of ECE, SIETK, PUTTUR

2. Time Division Multiplexing (TDM)

Frequency Division Multiplexing (FDM):

The FDM scheme with the simultaneous transmission of three signals is shown below

The Spectra of message signals and sum of the modulated carriers are indicated in the figure. In the figure DSB modulation is used for illustrating the spectra. Any type of modulation can be used in FDM as long as the carrier spacing is sufficient to avoid overlapping. The most widely used technique is SSB. At the receiving end of the channel the three modulated signals are separated by bandpass filters and then demodulated.

FDM is used in telephone system, telemetry, AM and FM broad casting.

Time Division Multiplexing (TDM):

In case division multiplexing, the complete channel bandwidth is allotted to one user for a fixed time slot. As an example, if there are ten users, then every user can be given the time slot of one second. Thus, complete channel can be used by each user for one second time for every ten seconds. This technique is suitable for digital signals.

There is a possibility of cross talk in FDM, whereas Inter Symbol Interference (ISI) is possible in TDM. These problems can be overcome by special cares.

Demodulation Methods for AM:

Square-Law Detector:


An AM signal can be demodulated by using a Square law device and then passing the signal through a lowpass filter as shown in figure.














Case II:

In Fig 15, the first carrier frequency c1 is selected as 100 KHz. The upper sideband of the output of product modulator1 ranges from 100.3 – 103 KHz. The selectivity of BPF1 must be 2*300 Hz=600 Hz at carrier frequency of 100 KHz; this is equal to 0.6% of 100 KHz.

Compared to first case, the designing of filter with 0.6% of 100 KHz is easy and simpler.

Case III:

Now, the upper side frequency of BPF1 is given as input to the Product modulator2, using a carrier frequency of 10 MHz. Then, the selectivity of the second bandpass filter must be 2 * 100.3 KHz

= 200.6 KHz at the carrier frequency of 10 MHz; this is equal to 2% of the 10 MHz.

Compared to first two cases the designing of BPF2 is much simpler.

Therefore, while generating SSB signals, if the carrier frequency is of MHz order, or more, the frequency translation must be done in two or more stages as shown in Fig 15.

Merits and Demerits:

The filter method is used for speech communication, where the frequencies range from 300 Hz – 300 KHz.

This method is not useful for video communication, where the frequencies are as low as d.c.

Phase Discrimination Method or Phase-shifting Method:

In this method, the time domain description of SSB-SC wave is considered asAnalog Communications 45 Dept. of ECE, SIETK, PUTTUR









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Unit-8sietkece.com/wp-content/uploads/2018/08/ACS-unit-I-NOTES.doc · Web viewInformation is a word or group of words with certain meaning. Information is central to communication