practical approach to frequency modulation and demodulation · sideband (dsbsc) modulation,...

International Journal of Engineering & Industry ISSN: 2191-3315, Volume 3, Issue 2, page 119 - 125

Zambrut

Zambrut.com. Publication date: July 18, 2019.

Aung, W. P., Shar, N. T. & Soe, L. N. 2019. Practical Approach to Frequency Modulation

and Demodulation ................

119

Practical Approach to

Frequency Modulation and

Demodulation

Wai Phyo Aung1, Nang Tee Shar

2 & Lay Nandar Soe

3

1Wai Phyo Aung,

2Nang Tee Shar &

3Lay Nandar Soe

1Ph.D (Electronics), Department of Electronic Engineering, TU (Loikaw)

2Demonstrator, TU (Loikaw)

3Lecturer, TU (Loikaw)

Loikaw, Kayah State, Myanmar

1. INTRODUCTION

Many different circuits have been devised to produce FM and PM signals. There are two

different types of frequency modulator circuits, direct circuits and circuits that produce FM indirectly

by phase modulation techniques. Methods of generating FM signals but they all basically involve an

oscillator with an electrically adjustable frequency. But for this experiment, we will generate a real FM

signal using the modules like voltage-controlled oscillators (VCOs) on the Emona DATEx trainer kit.

And there are several methods of demodulating an FM signal for example: using slope detector, the

Foster-Seeley discriminator, the ratio detector, the phase-locked loop and the zero crossing detectors.

We can analyze the waveforms and do comparisons with the theory due to the simulation results are

performed by waveforms. (Louis E. Frenzel Jr,2016).

Abstract: The aim of this paper is to practice the experiments with true mathematical

modeling hardware, designed specifically for implementing various communication

theories. The Emona DATEx telecommunication trainer kit with NI ELVIS II

PROTOYPING Platform draws on a well established experimental methodology that

brings to life the “universal language” of telecommunication, the BLOCK DIAGRAMS.

Focus examples of Emona DATEx trainer kit: Amplitude Modulation (AM), Double

Sideband (DSBSC) modulation, Frequency modulation and demodulation, PCM coding

and encoding, etc. Through this dissertation, this paper pointed out the operation of FM

modulation and demodulation theoretically. Also, FM transmitter-receiver is indeed an

electronic project that places great emphasis on practical work.

Keywords: Emona DATEx, telecommunication trainer kit, NI ELVIS II, PROTOTYPING

Platform, frequency modulation ,demodulation

https://zambrut.com/


https://zambrut.com/modulation-demodulation/


















Zambrut




120

1.1 Amplitude Modulation

As the name suggests, in AM, the information signal varies the amplitude of the carrier sine

wave. The instantaneous value of the carrier amplitude changes in accordance with the amplitude and

frequency variations of the modulating signal. The carrier frequency remains constant during the

modulation process, but its amplitude varies in accordance with the modulating signal. (Louis E.

Frenzel Jr,2016).

1.2 Phase Modulation

A type of modulation where the phase of the carrier signal is varied accordance to the low

frequency of the message signal is called phase modulation. (Louis E. Frenzel Jr,2016).

1.3 Frequency Modulation

It is the modulation where the frequency of the carrier signal is modulated (changed) in

proportion to the message signal while the phase and amplitude and amplitude are constant. (Louis E.

Frenzel Jr,2016).

2. FREQUENCY MODULATION AND DEMODULATION Frequency modulation (FM) is one of the angle modulation techniques. It can be found in any

kind of commercial radios and music synthesis, some systems that use video-transmission and also for

magnetic tape recording system. That kind of technique is mostly used in the field of

telecommunications and signal processing. For generating a frequency modulated signal, change in the

frequency of radio carrier is brought to be in line with the amplitude of the given incoming signal, there

is up and down movement in frequency of the newer frequency signal is the amount by which the

signal moves up and down. FM generation is quite easy. All that is needed a linear voltage to frequency

converter, something likes voltage controlled oscillator (VCO). A voltage controlled oscillator is an

electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input

voltage determines the instantaneous oscillation frequency.

Picture 1. Frequency modulation (Barry Duncan,2008)

In order to use the modulation on an FM signal, also it is necessary to extract the modulated

signal, i.e. demodulate or detect the signal. The frequency variations are converted into voltage for the

radio receiver in demodulation. A simple effective FM demodulator is one which takes a time average

of the zero crossings of the FM signal. Each pulse in the pulse train is fixed width, and is located at a

zero crossing of the FM signal. This is a pulse- repetition-rate modulated signal. If the pulse train is

passed through a low pass filter, the filter will perform an averaging operation. The rate of change of

this average value is related to the message frequency.


Zambrut




121

Picture 2. Waveforms resulting from modulating FM, comparator’s output and ZCD output

(Barry Duncan, 2008)

3. PRACTICAL APPROACH USING DATEx

For this experiment, the Emona DATEx experimental add-in module is used to help the

operation of electronic systems (like a radio transmitter for example). Block diagrams are used to

explain the principles without having to describe the details of how the circuit works. Each block

represents a part of the circuit that performs a separate task and is named according to what it does.

Examples of common blocks in communication equipment include the adder, filter, phase shifter and

so on.

Picture 3. Block diagram of recovering message signal from signals. (Barry Duncan,2008)

At the same time, there would be very few electronics laboratories or workshops that don’t also

have a DC power supply and Function Generator. So, the NI ELVIS II PROTOTYPE PCI SLOT can

be used to set up the trainer add-in module in this experiment. The NI ELVIS II sends the information

via USB to a personal computer where the measurements are displayed on the screen. On the computer,

the NIELVIS II devices are called “visual instruments”. However, don’t let the term mislead. The

digital multimeter and scopes are real measuring devices.

3.1 Generating FM signal

The master signals module is used to provide a 2 kHz square wave message signal and the VCO

is the FM modulator with a 20 kHz carrier. This procedure can be represented as shown in Picture 4.


Zambrut




122

Picture 4. Block diagram of generating FM signal. (Barry Duncan,2008)

By the idea of block diagram in Picture 4, we can connect the probes at EMONA DATAx

telecommunication with NI ELVIS II Protoype as shown in Picture 5.

Picture 5. Circuit Connection of FM using EMONA DATAx on NI ELVIS II Protoype

3.2 Setting up to complete the FM demodulation

Firstly, the comparator module on the Utilities module is used to clip the FM signal, effectively

turning it into a square wave. And the edge-triggered Twin-pulse generator module is used to

implement the zero-crossing detector. To complete the FM demodulator, the RC low pass filter module

and tunable low-pass filter combination is used to pick-out the changing DC component of the twin-

pulse generator module’s output. Block Diagram of this Demodulation Process is shown in Picture 6

and we can connect the probes of EMONA DATEx on NI ELVESII Prototype as shoen in Picture 7.

Picture 6. Block diagram of generating message signal from demodulation. (Barry Duncan,2008)


Zambrut




123

Picture 7. FM Demodulation Circuit connected in EMONA DATEx

4. TEST RESULTS

As testing result of this experimental approach , result photos are mentioned in Picture 8 to

Picture 12.

Picture 8. Simulation result of 2 kHz square wave signal

Picture 9. Simulation result of generating FM signal


Zambrut




124

Picture 10. Simulation result from the comparator on the Utilities module

Picture 11. Simulation waveforms resulting from Twin-pulse generator

Picture 12. Simulation of regenerating a message signal (a 2 kHz sine wave here) from demodulation


Zambrut




125

5. DISCUSSION AND CONCLUSION

As a conclusion, communication is a subject that really doesn’t touch in practically very much.

By this research paper, communication subject which is teaching for not only second year (EcE)

students but also other (EcE) courses can be improved for practical approach teaching. Without

external devices, likes oscilloscopes, multi-meters, function generators and spectrum analysizers, the

research only requires PC with appropriate software installed, the NI ELVIS II board and trainer

module. And also the DATEx has a collection of blocks (called modules) to implement dozens of

communication and telecommunications. The main empower person to be carried out this eperimental

research paper was second and third author, the first author is a supervisor of this Communication

Practical Approach.

6. REFERENCES

[1] Barry Duncan, Emona DATEx Telecommunictions Trainer Lab Manual Volume 1-Experiments in

Modern Analog and Digital Telecommunications for NI ELVIS II, 2008

[2] Louis E. Frenzel Jr., Principles of Electronic Communication Systems, 4th Ed, march, 2016

[3] Leon W. Couch II, Digital and Analog Communication systems, 8th Ed

[4] B.P. Lathi, Modern Digital and Analog Communication Systems, 3rd Ed, Oxford University Press,

1998

[5] “Communication Systems” 4th Ed.Simon Haykin.2001.

Zambrut Journal, Link Access;

https://zambrut.com


© Copyright International Journal of Zambrut | Zambrut, Inc.











practical approach to frequency modulation and demodulation · sideband (dsbsc) modulation,...

Documents