Web Based Virtual Analog Modulation Lab

لسنة -الرابعالعدد -المجلد السادس الجمعية العراقية لتكنولوجيا المعلومات4102

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Web Based Virtual Analog Modulation Lab

Assist. Prof. Dr. Saeed Obied Assist.Prof. Dr. Ibtesam R.Karhiy.Al-Saedi Dhamya Hussam

E-mail: [email protected] E-mail:[email protected] E-mail:[email protected] Al-Mansour Univesrity College University of Technology Al-Mansour Univesrity College

Communication Dept. Elecromichanical Eng. Dept. Internet Unit

Abstract The internet is considered as a very important mean to transfer the information

especially in the distance learning and the self –learning that enables the student to

receive the information and understand it in any place and time he or she is.

Due to the importance of labs especially in the field of engineering education and

because the equipments are not always available, their cost are high and many

problems face the student during making the experiment .For all these reasons have

motivated the researcher to design and implement a virtual lab (VL) to create an

environment for distance learning through internet pages using HTML language.

Computer techniques have been used to simulate the lab experiments.

Due to the importance of the communications subject in the curriculum of

communication engineering , the present work is directed to design and simulate a

VL for communication experiments for analog modulation. A MATLAB package is

used in design of the VL to carry out five experiments. This work is trying to prepare

VL in communication subject as a tool in e-learning environment.

الخالصه:يت وسيله مهمه جدا في نقل المعلومات وخاصه في مجال التعلم عن بعد وطرق التعلم الذاتي التي يعتبر األنترن

.يتواجد فيهووقت تمكن الطالب من أستالم المعلومات وفهمها في أي مكان م الهندسي ولعدم توفر االجهزه في أكثر االحيان وكلفتها يونظرا الهميه المختبرات وخاصه في مجال التعل

تصميم وتنفيذ مختبر الىالباحث دفعت ، تلك االسبابوالمشاكل التي قد تواجه الطالب اثناء أداء التجربه أفتراضي وخلق بيئه للتعلم عن بعد من خالل أستخدام صفحات االنترنيت التي تم تصميمها باستخدام لغه

.HTML المصممة ستخدام تقنيات الحاسوب في محاكاه التجارب المختبريهتم أ. مختبر ومحاكاة البحث الحالي على تصميم ركزفقد ضمن منهج هندسة االتصاالت وألهميه موضوع االتصاالت

في MATLAB“ " وقد تم أستخدام . ولموضوع التضمين التماثلي االتصاالتمادة أفتراضي لتجاربمختبر افتراضي يمثل البحث الحالي محاولة لبناء .تصميم المختبر االفتراضي الجراء خمس تجارب مختبريه

.كاحد ادوات التعليم االلكتروني

(VL), Analog Modulation, Amplitude Modulation, Angle Lab: Virtual Keywords

Modulation, MATLAB

1.Introduction :

The Internet provides many ways to enhance learning and expand educational

opportunities for students. Distance education and non-traditional classrooms,

for example, reach more students with specialized instruction and self-paced

learning [1].

In engineering education, written exercises are necessary for

undergraduate students to master conception while experimentations reinforce

the understanding of the subject. Real experiments are indispensable for

developing skills to deal with instrumentation and physical processes. There is


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no doubt that nothing will replace synchronous learning through face to face

interaction, but it is not always feasible for students to do experiment

uninfluenced. Virtual Lab (VL) can be treated as an accessorial tool of real

laboratory to enhance instruction for conventional on-campus students, which

can enable students to improve their skills before going to the actual laboratory

to learn breaking the restriction of ordinary arrangement and enhance the

instruction [2].

2. Theoretical background:

This paper has covered many concepts that was necessary to study and analysis

includes:

2 .1 Virtual Lab:

Virtual labs are software simulations of physical devices (e.g.

measurement instrument) or other real life systems (economic systems).

Computer animation and visualization can help to illustrate complex

relationships during classroom teaching as well as in individual learning at

home[3]. Virtual laboratories accessible via an Internet connection are

becoming a popular way to reduce equipment costs and bring laboratory

concepts into courses where it would be otherwise infeasible. These types of

labs commonly use MATLAB Simulink for the simulation software [1].

Virtual Lab technology can be used for aims of distance education.

When this approach is applied, then many advantages will be achieved by

simplifying the educational process. As a result, the number of internet

technology teaching users can be extended [4].

In this paper Virtual Lab on the web as a learning environment for

communication lab is used. els. Analog communication includes signal analysis

in time and spectral domains, signal modulation and signal detection.

Two types of signal modulations are simulated, namely, the Amplitude

Modulation (AM) and Angle Modulation.

Here, AM consists of the three classes (Double Sideband Large Carrier (DSB-

LC), Double Sideband Suppressed Carrier (DSB-SC), Single Sideband

Suppressed Carrier (DSB-SC), Quadrature Amplitude Modulation

(QAM)).Then Angle Modulation consists of the following two

classes(Frequency Modulation (FM), Phase Modulation (PM)).

2.2. Amplitude Modulation(AM):

AM is the process in which the amplitude of the carrier wave is varied in direct

proportion to the modulating signals .The carrier signal used has the general form:

)2cos()( tfAtc c

…………. …………….. (1)

where A is the amplitude and cf is the frequency of the carrier. In the frequency

domain, the carrier would appear as a pair of delta functions located at frequencies

of cf [5].


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DSB-SC signal is a class of AM signal that has a suppressed discrete carrier.

The DSB-SC signal is given by

tc

tmtsDSB

cos)()( …………. …………….. (2)

The spectrum of the DSB- SC is [6].

….…………. …….… (3)

The component of frequency c is the Upper Sideband, and that of

frequency c is the Lower Sideband [7]. Recovering the modulating signal

)(tm from the modulated signal )(tsDSB

using synchronized oscillator is called

synchronous detection. The coherent detection consists of multiplication of the

incoming modulated signal )(tsDSB

by a local carrier )cos( tc

as given by

the equation below:

)2cos()(2

1)(

2

1)cos()()( ttmtmttste ccDSB ………. ………….….. (4)

Therefore the Fourier transform of both sides of the equation is

)2(4

1)2(

4

1)(

2

1)( cc MMME ………. ……………... (5)

Then the product is passed through the low pass filter which allows the

desired spectrum )(M to pass and suppress the unwanted high frequency

spectrum center at c2 [7]. The DSB-SC signal can be generated by

multiplying the message signal with the carrier using multiplier circuit as

shown in Fig. (1).

Fig.( 1) Simulink simulator of DSB-SC modulation and demodulation scheme.

)()()(2

1ccDSB MMS


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To generate a DSB-LC signal is accomplished by first generating DSB-SC

signal and then adding some carrier as shown in the block diagram form in Fig.

(2) [8]. The transmitted signal is expressed mathematically as:

ttmAts cAM cos))(()( …………. ……………..

(6)

Fig.( 2) Simulink simulator of DSB-SC modulation and demodulation scheme.

In AM (DSB-LC) a very simple scheme known as envelope detection

can be used for demodulation if sufficient carrier power is transmitted. The

envelope detector circuit is shown in Fig. (3). It comprises a diode followed by

an RC circuit. When the input voltage is positive, the capacitor charges (with

time constant CrDf , where rDf is the diode resistance in forward direction).

When the input goes negative, the diode becomes an open circuit and the

voltage on the capacitor exponentially decays (i.e., natural response) at a rate

determined by the time constant ( =RC The choosing to the time constant

of the RC circuit depends on the carrier frequency and message frequency. A

rule of thumb is to use.

BRC

fc

11 …………. …………….. (7)

where fc is the carrier frequency in Hz and B is the bandwidth of the message

signal[9]. A best approximation for proper envelope detection is [10]

m

RC

21 ……………………… (8)

where is the modulation index.

Fig (3) shows the detector output for different values of RC


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Because of AM modulation and DSB modulation require the double bandwidth

of a given signal. Since either the upper sideband or the lower sideband

contains the complete information about the message signal, therefore doubling

of the bandwidth using AM or DSB is a waste of the bandwidth, especially

when a given band of frequencies is crowded [10]. When only one sideband is

transmitted, the modulation is referred to as single sideband (SSB) modulation

SSB generation can be carried out by two methods: The filter method and the

phasing method:

A- Filter Method:

The straightforward way to generate an SSB signal is to generate a DSB

signal first and then suppress one of the sideband by band-pass filtering with

transfer function H( )[8].

Fig. (4) Simulink simulator of SSB modulator scheme using filter

B- Phasing Method:

The modulated signal is represented by [11]

ttmttmS ccSSB sin)(cos)(

……………… (9)

For demodulation, the spectral density of SSB signal must be translated

back to 0 . This operation can be achieved using synchronous detection.

Multiplication of the SSB signal by tccos translates half of each spectral

density up in frequency by c rad/sec and half down by the same amount ,as

shown in Fig.(5). That portion shifted up to a frequency of c2 can be filtered

with a low- pass filter [8].

]2sin2cos)([2

1cos

2

1cos tmttmtts ccmcSSB ……………………. (10)


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Fig.(5) Simulink simulator of SSB-LSB modulation and demodulation scheme.

2.3 Quadrature Amplitude Modulation (QAM) DSB signal occupy twice the bandwidth required for SSB signal. This

disadvantage can be overcome by transmitting two DSB signals using carrier of

the same frequency but in phase quadrature, as shown in Fig (6) [6].

Since )sin( tm and )cos( tm are orthogonal functions, the principle of

quadrature multiplexing of two signals is to transmit one signal using a carrier

of the form )cos( tc and to transmit the other signal using a carrier of the other

of the from )sin( tc as given by the equation below [12]:

)2sin()()2cos()()( 21 fcttmfcttmts …………. ……………..

(11) The original signals can be recovered at the receiver by synchronous detection

using two local carriers of the same frequency but in phase quadrature. This can

be shown by considering the multipliers output )(1 tx and )(2 tx of channel 1 and

2 respectively Fig. (6).

ttmttmtmttstx ccc 2sin)(2

12cos)(

2

1)(

2

1)cos()()( 2111 .. (12)

ttmttmtmttstx ccc 2cos)(2

12sin)(

2

1)(

2

1)sin()()( 2122 .. (13)

The terms of c2 are suppressed by low pass filters, yielding the desired

outputs )(1 tm and )(2 tm [12]:

)(2

1)( 11 tmte …………. …………….. (14)

)(2

1)( 22 tmte …………. …………….. (15)


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Fig. (6) Simulink simulator of QAM and demodulation scheme

3. Angle Modulation:

Angle modulation is a kind of modulation in which the amplitude of

the modulated signal is kept constant and its angle is varied in accordance with

the modulating signal. Phase Modulation (PM) and Frequency Modulation

(FM) are two special cases of angle modulated signaling. The general form of

these modulated signals is given by

))(cos()( ttAts c …………………………………………(16)

Hence

)()( ttt ci ……………………………………….(17)

where )(ti is the instantaneous phase, c the carrier frequency, and )(t is the

instantaneous phase deviation of the modulated signal )(ts . The derivative of

)(ti is termed as the instantaneous frequency.

dt

td

dt

tdc

ii

)()(

…………………………………….(18)

The quantity defined by

ci max ……………………………………… (19)

is the maximum (or peak) radian frequency deviation[10].

The dependency of )(t on the modulating signal )(tm determines the type of

modulation.

In FM, the instantaneous phase deviation )(, tFMi is proportional to the

integral of message; that is

t

t

fFMi dmkt

0

)()(, …………………………. (20)

where fk is the frequency deviation constant expressed in radian per second per

unit of )(tm [10].when Eq. (20) is substituted in Eq. (17) the phase angle of FM

is therefore;


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t

t

fcFMi dmktt

0

)()(, ………………...………… (21)

The instantaneous frequency of FM signal is

)()(

,tmk

dt

tdfc

i

FMi

………………………………..(22)

Thus ; In FM the instantaneous frequency is proportional to the message .

From Eq.(19) the peak frequency deviation is

)(maxmax tmk fciFM ……………………………….(23)

The FM signal according to Eq. (16), can be expressed as

])(cos[)(

0

t

t

fcFM dmktAts ………………………..… (24)

it is apparent that PM and FM are not only very similar but inseparable. In fact,

by looking at an angle-modulated carrier, there is no way of telling if it is FM

or PM because a PM wave obtained by feeding )(tm to phase modulator can

also be obtained if )(tm is fed to frequency modulator Fig. (7a) and an FM

wave obtained by feeding )(tm to frequency modulator can also be obtained if

t

t

dm

0

)( is fed to Phase Modulator Fig. (7b).

Fig (7) The relationship between the FM and PM generation

(a) Generation PM wave.

(b) Generation FM wave.

Fig. (8) Simulink simulator of Frequency Modulation by using the Frequency Modulator.


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Fig. (9) Simulink simulator of Frequency Modulation by using the Phase Modulator.

Also, There are two methods of generating wideband frequency

modulated signal (WBFM); the indirect method and the direct method.

A- The Indirect Modulation:

In this method, a WBFM signal is produced first as shown in Fig. (10).

To generate wideband FM, the modulation index must be increased to higher

value. This can be done by using frequency multiplier which is nonlinear

device designed to multiply the frequency of the input signal by a given factor.

A simple square-law device, for example, can multiply the input frequency by a

factor of 2. The input –output characteristic of an ideal square –law device is[8]

)()(2

tcete io …………………..……. (25)

If the input signal is the FM signal

)sincos()()( tctAtste mFMi ………..….. (26)

the output is

)sin(cos)( 22 tctcAte mo …………. (27)

Fig (10) Block diagram of Armstrong FM transmitter

B- Direct Frequency Modulation:

An oscillator whose frequency can be controlled by an external

voltage is called a "Voltage Control Oscillator (VCO)". In a VCO, the

oscillation frequency varies linearly with the Control Voltage [6]. So, an FM

wave can be generated by using a VCO controlled by the modulating signal

)(tm . A common method for controlling oscillator frequency is to vary the

inductance or capacitance of a tuned electronic oscillator. The oscillation

frequency is given by

LC

10 …………………………………..(28)


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If the capacitance C is varied by the modulating signal )(tm ,the oscillator

frequency will be the FM instantaneous frequency[7]. Thus if

)(0 tkmCC ………………………….. (29)

then

21

0

0

0

0

0

])(

1[

1

])(

1[

1

C

tkmLC

C

tkmLC

i

… ………………(30)

For 1)( tkm

]2

)(1[

1

00C

tkm

LCi ………………………………………..(31)

)(tmk fci ……………………………………(32)

0

1

LCc

00022* C

k

CLC

kk c

f

………………………………..(33)

4. Demodulation of Fm Signal:

Two methods of demodulating FM signals are discussed. The first one

uses frequency discriminator and the second uses Phase-Locked Loop (PLL).

A- Demodulation With Discriminator:

In an FM wave, the information signal is present in the instantaneous

frequency )(tmk fci . Hence, a frequency selective network that

produces an output proportional to the instantaneous frequency deviation of the

input signal is required. Such a system is called a frequency discriminator,

which is a differentiator followed by an envelope detector . The output is

t

t

fcfcFMFM dmkttmkAtsdt

tds

0

])(sin[))(()()(

………… (34)

If )0)()(( tmktmk fcfc at all time, then Eq.(34) is a form of an AM

signal whose envelope is

))(1())(( tmkA

tmkAc

f

c

fc

……………………..(35)

The modulating signal )(tm can be obtained by envelope detector of

)(ts FM [7,10].


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B- Phase Locked Loop (PLL):

Phase locked loop is a circuit which synchronizes (locked state) the frequency

or phase of this inputs [11]. A PLL consists of multiplier that serves as a phase

comparator (PD), a loop filter and a VCO as shown in Fig. (11)[6].

Fig.(11) Basic PLL

The phase comparator produces an output signal )(1 tv that is a function of the

phase difference between the incoming signal )(tvinand the oscillator

output )(tvo. The filtered signal )(2 tv is the control signal that is used to

change the frequency of the VCO output.

Assume the input signal is

))(sin()( ttAtv iciin ………….. …… (36)

and that of the VCO output signal is

))(cos()( ttAtv ocoo ………….. ……… (37)

Where

t

t

vo dvkt

0

)()( 2 ……….…………… (38)

and vk is the VCO gain constant then the PD output is

))]()(2sin())()([sin(2

)(

))(cos())(sin()(

1

1

tttttAAk

tv

ttttAAktv

oicoioim

ocicoim

……… (39)

where mk is the gain of the multiplier circuit. The sum frequency term does not

pass through the LPF, so the LPF output is

)(*)]([sin)(2 tftktv ed …………………………….(40)

where )()()( ttt oie ………………………(41)

2

oimd

AAKk ……………………. (42)

and )(tf is the impulse response of the LPF. )(te is called the phase error,


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The overall equation describing the operation of the PLL circuit may be

obtained by taking the derivative of Eqs (38) and (41)and combining the result

by the use of Eq.(40)[4]. In Fig.(12) that shows Analog PLL, The VCO phase is

given by

……………………..(43)

For FM wave

dmkt

t

t

fi

0

)()( ……………………..(44)

Hence

)()()(

0

tdmkt e

t

t

fo ………………………

(45)

and

)()(1

)(2 tmk

kt

ktv

v

fo

v

………………………….. (46)

Thus the PLL acts as an FM demodulator [7].

Fig.(12)Analog PLL

5 Web Based Virtual Lab:

The laboratory is a very important part in engineering education. In

fact, heavy weighting in practical training dominates technical education [13].

In this paper, Virtual Lab system in the subject of Analog Modulation System

is used for students who study engineering. The design of this Virtual Lab

involves simultaneous use of the Web browser and MATLAB Simulink.

The design of this Virtual Lab involves simultaneous use of the web

browser and any application package. Students can stay at home to do

experiments through their computers via the internet . As student submits

answers and comments to the laboratory through the web. The communication

among students and the interaction between the student and teacher are

supported through e-mail. The teacher can monitor the results of each student

)()( 2 tvkt vo


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and help students with problems. Virtual Lab is used for experiment in

simulation and virtual instrumentation analysis and design.

Educational technology is a discipline whose main object is to study the

relation between education and technology. It includes instructional design and

planning, teaching methods (e.g. simulations), instructional media (such as

computers and hypermedia), instructional resources, learning (including study

skills, learning theories, motivation and problem solving), and assessment and

evaluation [14]. Therefore, this work depends on the principle of engineering

education in design, implementation, and evaluation.

The current Virtual Lab includes the following parts:

• Objective: This section contains the main objective of the experiment.

• Equipments: This section contains equipment used for implementing the

experiment from MATLAB Simulink.

• Background information: This section contains all necessary basic concepts

and theorems to perform experiments in the Virtual Lab. The students can

easily review the basic knowledge learned in the class before going to the

procedure section of the Virtual Lab or they can refer back to this section if

they find something that is not clear.

• Creating the Simulink model: This section includes procedure

implementation experiment by using MATLAB Simulink for students to

perform experiment at any time and any place and they can download

experiment from the web page and change the parameters and value.

• Interactive questions: This part includes questions of true or false answers. If

the answer is the true , the small window will appear to tell the reader that the

answer is true. If the answer is false, the small window will appear to tell the

reader that the answer is false.

6. Design and Implementation of Web Page for the Simulator:

The web page used in simulation Experiments is presented in this

section. The menu of web page driven interactive includes the Virtual Lab

Experiments simulators that contain the name of experiments. The user can

operate the simulator for any one of experiment. The main window appears

anew is shown in Fig. (13).


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The student clicks on the creating the Simulink, a model will appear on the screen

as shown in Fig.(14). This screen includes the procedure for performing experiment

and includes the running model. The user can obtain this experiment and can

change the parameter of the experiment that happen when the user clicks block of

the DSB-SC where will be appeared screen as shown in Fig. (15) where the

MATLAB is found in the PC, the students can open and save experiment.

Fig.(15) The download operation to the experiment from the web

7.Simulation Results

The simulation results of the various software-designed experiments simulators,

which are given in the previous. The effect of changing different system

parameters on the input and output signals is considered throughout all the

experiments. Also this effect is viewed clearly in the graphs.

Fig.(13) The window of name of experiment

Fig.(14) The window includes block diagram for generation DSB-SC


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In DSB-SC Experiment Simulation Result, The simulation model of the

transmitter and receiver is implemented as in Fig. (16) that used Simulink

environment. In this experiment a 5KHZ sinusoidal modulating signal is used.

The carrier frequency chosen in this causes is 600KHZ. The spectrum of

modulated signal consists of two sidebands, namely the upper and lower –

sidebands as indicated in the figure.

The figures 17, 18 and 19 show the patterns of the results that VL had coverd..

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x 10-3

-1

-0.5

0

0.5

1

time(sec)

Ampli

tude

(a) (b)

Fig (16) 5KHZ modulating signal (a) in time domain (b) in frequency domain.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x 10-5

-1

-0.5

0

0.5

1

time(sec)

Am

plitu

de

0.54 0.56 0.58 0.6 0.62 0.64 0.66 0.68 0.7

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Frequency (MHz)

Ampli

tude

Fig (17) 600KHZ carrier frequency (a) in time domain (b) in frequency domain.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x 10-3

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

time(sec)

Ampl

itude

0.58 0.585 0.59 0.595 0.6 0.605 0.61 0.615 0.62 0.625 0.63

0.05

0.1

0.15

0.2

0.25

Frequency (MHz)

Ampli

tude

USBLSB

Fig (18) Modulated signal: cosωmt * cos ωct fm=5KHZ and fc =600KHZ

(a) in time domain (b) upper and lower sideband spectrum.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x 10-3

-1

-0.5

0

0.5

1

time(sec)

Am

plitu

de

(a) (b)

Fig (19) Demodulated DSB-SC signal for fm=5KHZ


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(a) in time domain (b) signal in frequency domain.

Conclusions:.8

Based on the analysis and results which presented in this work the

following conclusions are drawn:

1. The Virtual Lab provides the learner with necessary skill that he can

acquire from using the traditional laboratory.

2. Simulink has solved some problems which are met in real or physical

Lab.

3. The students have learned operating the spectrum, oscilloscope and the

function generator to view different waveforms schemes(DSB-SC,DSB-

LC,SSB,QAM,FM)

4. The web environment assists instructors in classrooms as the teaching

and learning process can be continued out of the teaching scheduled

hours and anywhere.

5. The simulation system allows students to remotely and easily run an

experiment lab simulation on a server through the internet without

platform dependency using a web-browser.

9. Reference

[1] Poindexter, Sandra E.,” Using the Web in Your Courses: What Can you Do?”.

IEEE Control Systems Magazine, vol. 19, NO. 1, February 1999,

http://www.nmu.edu/college/cob/faculty/spoindex

[2] Hesselink,Lambertus,” internet assisted loboratories (I-labs)”, internet search ,

26 march 2001.

[3] Miaoliang, Zhu and Yabo,Dong, "A Case Study of Virtual Circuit Laboratory

for Undergraduate Student Courses", College of Computer Science and

Technology,Zhejiang University,, July 2005.

[4] I.S ,Maksimov., G.I ,Churyumov,“The Concept of Simulation Results Display

in the Research Activities And Distance Education”,Kharkov National University

of Radio Electronics, 2002.

[5]Townsend,Rachel,”Modulation”,

http://www.ee.newcastle.edu.au/users/staff/eemf/MinyuFu.html

[6] W. L. Couch,"Digital and Analog Communication System”, USA, sixth ed., July

2002.

[7] B.p Lathi “Modern Digital and Analog communication systems”Orlando,

Florida 1998.

[8] FerrelG.Stremler, ”Introduction to communication system “,Addisson –wesely

1994.

http://www.nmu.edu/college/cob/faculty/spoindex

http://www.ee.newcastle.edu.au/users/staff/eemf/MinyuFu.html


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[9] R. C. Hardie,” LAB 3: AM Modulation and Demodulation”

, Department of Electrical and Computer Engineering, University of Dayton, ECE

401L COMMUNICATIONS LABORATORY, 2003.

[10] Scham's,"Analog and Digital communications",MC GRAW-HiLL,2003

[11] ” angle modulation Lab” Electrical Engineering Department, University –

Multidisciplinary Initiative on Distance Learning – ASU, 2000.

http://www.eas.asu.edu/~midle/jdsp/commex/JDSP_NEW_thesis/LAB2_ANGLE_M

OD.htm

[12] “Analog Modulation”, internet search,

http://www.home.online.no/lilandh/hfKmm2/amfmmod.pdf

[13]K.C.Chu , Dennis Leung,"Flexible Learning Via Web-Based Virtual Teaching

and Virtual Lab System", Electrical and communication Engineering Department

,Hong Kong Technical College ,2001

[14]Multisilta,Jari,”Hypermedia Learning Environment for Mathematics”, Ph.D

Thesis, Technology Department, University of Technology, 1996.

http://www.eas.asu.edu/~midle/jdsp/commex/JDSP_NEW_thesis/LAB2_ANGLE_MOD.htm

http://www.eas.asu.edu/~midle/jdsp/commex/JDSP_NEW_thesis/LAB2_ANGLE_MOD.htm

http://www.home.online.no/lilandh/hfKmm2/amfmmod.pdf

Web Based Virtual Analog Modulation Lab

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