DATA COMMUNICATION TRAINER

LAB ELECTRONICS

NEW#5, II FLOOR, 10TH AVENUE, ASHOK NAGAR, CHENNAI-83

DATA COMMUNICATION TRAINER

MODEL -X31

OBJECTIVE:

To study the following experiments through AT89C51 using the Data formats such as

NRZ, RZ, and Manchester.

Data Formatting

Amplitude Shift Keying (ASK)

Frequency Shift Keying (FSK):

Phase Shift Keying (PSK)

Quadrature Phase Shift Keying (QPSK)

MATERIALS REQUIRED:

DATA COMMUNICATION TRAINER, Model X-31

Patch cords

Oscilloscope

INTRODUCTION:

The LAB ELECTRONICS DATA COMMUNICATION TRAINER, Model

X-31 is designed to help the students to understand the concepts of DATA

Communication. Students can conduct experiments on modulation & demodulation

through 8-Bit Microcontroller. The AT89C51 is a low-power, high-performance CMOS

8-bit microcomputer with 4K bytes of Flash Programmable and Erasable Read Only

Memory (PEROM). The device is manufactured using Atmel’s high-density nonvolatile

memory technology and is compatible with the industry standard MCS-51™

instruction set and pin out. The on-chip Flash allows the program memory to be

reprogrammed in-system or by a conventional nonvolatile memory programmer.

LAB ELECTRONICS

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By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel

AT89C51 is a powerful microcomputer which provides a highly flexible and cost

effective solution to many embedded control applications.

FEATURES OF THIS TRAINER:

1. MODULATOR & DEMODULATOR CONTROLLERS 89C51

Compatible with MCS-51™ Products

4K Bytes of In-System Reprogrammable Flash Memory

Endurance: 1,000 Write/Erase Cycles

Fully Static Operation: 0 Hz to 24 MHz

Three-Level Program Memory Lock

128 x 8-Bit Internal RAM

32 Programmable I/O Lines

Two 16-Bit Timer/Counters

Six Interrupt Sources

Programmable Serial Channel

Low Power Idle and Power Down Modes

Reset Switch To Reset Both Controllers.

2. CARRIER SOURCE:

Output Waveforms : Sine Cosine

Frequency Range : 1 KHz to 20 KHz. 1 KHz to 20 KHz

Amplitude Range : 0 -9V (P-P) 0 -9V (P-P).

3. Built-in power supply : +12V/1A: 5V /1A

4. Data Selector Switch : 8 bit data output Data LO

Data HI

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MSB LSB

5. Mode selector switch: MSB LSB FUNCTION

X 0 0 0 ASK

X 0 0 1 FSK

0 0 1 0 PSK

1 0 1 1 QPSK

X 1 0 0 NRZ

X 1 0 1 RZ

X 1 1 0 MANCHESTER

NOTE: 7 LEDS are provided to observe the corresponding enabled mode.

6. Functional Block Diagram: ASK, FSK, PSK and QPSK Modulation/Demodulation.

LSB

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LIST OF EXPERIMENTS:

1. Data formatting

NRZ (Non-Return to Zero)

RZ (Return to Zero)

MANCHESTER

2. MODULATION & DEMODULATION (MODEM)

Amplitude Shift Keying (ASK)

Frequency Shift Keying (FSK)

Phase Shift Keying (PSK)

Quadrature Phase Shift Keying (QPSK)

PRECAUTIONS TO BE TAKEN:

ALWAYS SWITCH OFF THE TRAINER WHILE PATCHING THE CIRCUIT. DO

NOT SHORT CIRCUIT BY PATCHING SUPPLY POINT TO THE GROUND

TERMINAL PROVIDED IN THE TRAINER.

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DATA FORMATTING

EXPERIMENT-1

OBJECTIVE:

To study the Data Formatting.

MATERIALS REQUIRED:

1. LAB DATA COMMUNICATION Trainer.-2, Model X-31

2. oscilloscope

3. Set of Patching Chords.

THEORY OF DATA FORMATTING:

The symbols ‘0’ and ‘1’ in digital systems can be represented in various formats

with different levels & waveforms. The selection of particular format for communication

depends on the system bandwidth, system's ability to pass DC level information, error

checking facility, case of clock regeneration & synchronization at receiver, system

complexity & cost etc.

The most widely used formats of data representation are given below. Every data

format has specific advantages & disadvantages associated with them.

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NON - RETURN TO ZERO (LEVEL) NRZ (L):

It is the simplest form of data representation. The NRZ (L) waveform simply

goes low for one bit time to represent a data '0' & high for one bit time to represent a

data ‘1’. Thus the signal alternates only when there is a data change.

In telecommunication, a non-return-to-zero (NRZ) line code is a binary code, in

which "1s" are represented by one significant condition and "0s" are represented by

the other significant condition, with no other neutral or rest condition. The pulses have

more energy than a RZ code. Unlike RZ, NRZ does not have a rest state. NRZ is not

inherently a self-synchronizing code, so some additional synchronization technique

(perhaps a run length limited constraint or a parallel synchronization signal) must be

used to avoid bit slip. For a given data signaling rate, i.e., bit rate, the NRZ code

requires only half the bandwidth required by the Manchester code. When used to

represent data in an asynchronous communication scheme, the absence of a neutral

state requires other mechanisms for data recovery, to replace methods used for error

detection when using synchronization information, a separate clock signal is available.

NRZ-Level itself is not a synchronous system but rather an encoding; this can be used

in either a synchronous or asynchronous transmission environment, that is, with or

without an explicit clock signal involved.

Because of this, it is not strictly necessary to discuss how the NRZ Level

encoding acts "on a clock edge" or "during a clock cycle", since all transitions happen

in the given amount of time representing the actual or implied integral clock cycle.

http://en.wikipedia.org/wiki/Telecommunication

http://en.wikipedia.org/wiki/Line_code

http://en.wikipedia.org/wiki/Binary_coding

http://en.wikipedia.org/wiki/Significant_condition

http://en.wikipedia.org/wiki/Return-to-zero

http://en.wikipedia.org/wiki/Self-synchronizing_code

http://en.wikipedia.org/wiki/Run_length_limited

http://en.wikipedia.org/wiki/Bit_slip

http://en.wikipedia.org/wiki/Data_signaling_rate

http://en.wikipedia.org/wiki/Bit_rate

http://en.wikipedia.org/wiki/Bandwidth

http://en.wikipedia.org/wiki/Manchester_code

http://en.wikipedia.org/wiki/Asynchronous_communication

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The real question is that of sampling the high or low state which will be received

correctly provided the transmission line has stabilized for that bit when the physical

line level is sampled at the receiving end. However it is handy to see NRZ transitions

as happening on the trailing (falling) clock edge in order to compare NRZ-Level to

other encoding methods, such as the mentioned Manchester code, which requires

clock edge information (is the XOR of the clock and NRZ) and to see the difference

between NRZ-Mark and NRZ-Inverted.

STEP BY STEP PROCEDURE:

STUDY OF NRZ OUTPUT :

1. Switch on the trainer

Mode selection

2. To study Data formatting set the Mode selection switches as in the following

position: Mode selection switch is used to select the modulation as well as Data

formatting types.

S1 S2 S3 S4 Mode

X 1 0 0 NON RETURN TO ZERO

Note: Depress -reset switch after changing each mode.

Example:

Change the mode selector as ‘X100’ and then press RESET switch for

selecting Return to Zero data formatting.

X’-defined as don’t care, i.e., which doesn’t affect the process.

2. Now set the data selection switch to HI /LO position to get serial data stream from

microcontroller.

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DATA SELECTION:

8-Bit Data selector is used to give the data parallel to the controller.

S1 S2 S3 S4 S5 S6 S7 S8

D7 D6 D5 D4 D3 D2 D1 D0

MSB LSB

Data selector switch is used to select the data. If the switch position is upward

‘ ‘ then logic ‘1’ is given.

If dip switch is in downward position ‘ ‘then logic ‘0’ is given.

Observe the NRZ output at data formatting terminal.

Data is formatted according to data selector.

RZ: Return-to-zero (RZ) describes a line code used in telecommunications signals

in which the signal drops (returns) to zero between each pulse. This takes place even

if a number of consecutive zeros or ones occur in the signal. The signal is self-

clocking. This means that a separate clock does not need to be sent alongside the

signal, but suffers from using twice the bandwidth to achieve the same data-rate as

compared to non-return-to-zero format.

The "zero" between each bit is a neutral or rest condition, such as a zero

amplitude in pulse amplitude modulation (PAM), zero phase shift in phase-shift

keying(PSK), or mid-frequency in frequency-shift keying (FSK). That "zero" condition

is typically halfway between the significant condition representing a 1 bit and the other

significant condition representing a 0 bit.

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Although return-to-zero (RZ) contains a provision for synchronization, it still has a DC

component resulting in “baseline wander” during long strings of 0 or 1 bits, just like the

line code Non-return-to-zero.

STUDY OF RZ OUTPUT

MODE SELECTION

1. To study Data formatting set the Mode selection switches as in the following

position: Mode selection switch is used to select the modulation as well as Data

formatting types.

S1 S2 S3 S4 Mode

X 1 0 1 RETURN TO ZERO

Note: Depress reset switch after changing each mode.

Example:

Change the mode selector as ‘X101’ and then press RESET switch for

selecting Return to Zero data formatting.

‘X’ is defined as don’t care, i.e., which doesn’t affect the process.

2. Now set the data selection switch to HI /LO position to get serial data stream from

microcontroller.

DATA SELECTION:

8-Bit Data selector is used to give the data parallel to the controller.

S1 S2 S3 S4 S5 S6 S7 S8

D7 D6 D5 D4 D3 D2 D1 D0

MSB LSB

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Data selector switch are used to select the data. If the switch position is upward

‘ ‘then logic ‘1’ is given.


3. If the controller is working in the RZ Data formatting mode. You will observe RZ

Data in the Data Formatting Output terminal.

4. Micro Controller port P0.0 & 0.1 gives the corresponding data formatted output

according to the input data stream.

5. The O/P is connected from microcontroller to data formatting terminal.

RZ OUTPUT

MANCHESTER CODE:

Manchester code (also known as Phase Encoding or PE) is a line code in which

the encoding of each data bit has at least one transition. It is therefore self-

clocking, which means that a clock can be recovered from the encoded data. Each

bit occupies the same time. Manchester code is widely used (e.g. in Ethernet).

There are more complex codes e.g. 8B/10B encoding which use less bandwidth to

achieve the same data rate (but which may be less tolerant of frequency errors

and jitter in the transmitter and receiver reference clocks).

Manchester code provides simple encoding with no long period without a level

transition. This helps clock recovery. The DC component of the encoded signal is

equal to zero and therefore carries no information, so that the signal can be

conveyed conveniently by media (e.g. radio) which usually do not convey a DC

component.

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SUMMARY:

Each bit is transmitted in a fixed time (the "period").

A 0 is expressed by a low-to-high transition, a 1 by high-to-low transition. The

transitions which signify 0 or 1 occur at the midpoint of a period.

Transitions at the start of a period are overhead and don't signify data.

Manchester code always has a transition at the middle of each bit period and

may (depending on the information to be transmitted) have a transition at the start of

the period also. The direction of the mid-bit transition indicates the data. Transitions at

the period boundaries do not carry information.

They exist only to place the signal in the correct state to allow the mid-bit

transition. Although this allows the signal to be self-clocking, it doubles the bandwidth

requirement compared to NRZ coding schemes (or see also NRZI).

In the Thomas convention, the result is that the first

half of a bit period matches the information bit and the second half is its complement.

MANCHESTER ENCODING AS PHASE-SHIFT KEYING

Manchester encoding is a special case of binary phase-shift keying (BPSK),

where the data controls the phase of a square wave carrier whose frequency is the

data rate. Such a signal is easy to generate.

To control the bandwidth used, a filter can reduce the bandwidth to as low as

1Hz per bit/second without loss of information in transmission. However, for practical

reasons (and to limit bandwidth consumption further, especially on crowded radio

bands), most BPSK modulators choose a carrier frequency much higher than the data

rate, resulting in tighter, more easily filtered bandwidths, but the property of 1Hz per

bit/second is preserved.

CONVENTIONAL REPRESENTATION OF DATA:

http://en.wikipedia.org/w/index.php?title=Bit_period&action=edit

http://en.wikipedia.org/wiki/Non-return-to-zero

http://en.wikipedia.org/wiki/NRZI

http://en.wikipedia.org/wiki/Phase_shift_keying#Binary_phase-shift_keying_.28BPSK.29

http://en.wikipedia.org/wiki/Phase_%28waves%29

http://en.wikipedia.org/wiki/Carrier_wave

http://en.wikipedia.org/wiki/Electronic_filter

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Encoding of 11011000100 in Manchester code

There are two opposing conventions for the representation of data.

It specifies that for a 0 bit the signal levels will be Low-High (assuming an

amplitude physical encoding of the data) - with a low level in the first half of the bit

period, and a high level in the second half. For a 1 bit, the signal levels will be High-

Low.

It states that logic 0 is represented by a High-Low signal sequence and logic 1 is

represented by a Low-High signal sequence. If a Manchester encoded signal is

inverted in communication, it is transformed from one convention to the other.

This ambiguity can be overcome by using differential Manchester encoding.

Manchester code needs twice the bandwidth of asynchronous communication and the

signal spectrum is much wider. Most high-speed communication now uses encoding

schemes with better coding performance.

One consideration is synchronization of the receiver to the transmitter. It might appear

that a half bit period error would give an inverted output at the receiver, but for typical

data this leads to code violations. The receiver can detect these violations and use

this information to synchronize accurately.

STUDY OF MANCHESTER CODING

1. To get Manchester coding, mode selection should be ‘X 1 1 0’.

2. Observe the Manchester coding output at the data formatting terminal.

3. Data is formatted according to data selector.

http://en.wikipedia.org/wiki/Differential_Manchester_encoding

http://en.wikipedia.org/wiki/Bandwidth

http://en.wikipedia.org/wiki/Asynchronous_communication

http://en.wikipedia.org/wiki/Signalling_%28telecommunication%29

http://en.wikipedia.org/wiki/Electromagnetic_spectrum

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EXPERIMENT-2

ASK MODULATION AND DEMODULATION

OBJECTIVE:

To study the ASK Modulation and Demodulation.

MATERIALS REQUIRED:

1. LAB DATA COMMUNICATION Trainer , Model X-31.

2. Oscilloscope

3. Set of Patching Cords.

INTRODUCTION:

CARRIER MODULATION

To transmit the digital data from one place to another, we have to choose the

transmission media. The simplest possible method to connect the transmitter to the

receiver with a piece of wire. This works satisfactorily for short distances in some

cases. But for long distance communication & in situations like communication with

the aircraft, ship, and vehicle this is not feasible. Here we have to adopt for the radio

transmission.

It is not possible to send the digital data directly over the antenna because the

antennae of practical size work on very high frequencies, much higher than our data

transmission rate. To be able to transmit the data over antenna, we have to 'modulate'

the signal's phase; frequency or amplitude etc is varied in accordance with the digital

data. At receiver we separate the signal from digital information by the process of

demodulation. After this process we are left with high frequency signal (called as

carrier Signal) which we discard & the digital information, which we utilize.

Modulation also allows different data streams to be transmitted over the same

channel (transmission medium). This process is called as 'Multiplexing' & result in a

considerable saving in no. of channels to be used. Also it increases the channel

efficiency. The variation of particular parameter variation of the carrier wave gives rise

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to various modulation techniques. Some of the basic modulation techniques are

described as under.

(A) Amplitude Shift Keying (ASK)

In these techniques modulation involves the variation of the amplitude of the

carrier- wave in accordance with the data stream.

B) Frequency Shift Keying (FSK):

In these techniques modulation involves the variation of carrier frequency with the

data information.

(C) Phase Shift Keying (PSK):

In this technique, the phase of the carrier frequency is varied in accordance

with the data stream. The selection of particular modulation method used is

determined by the application intended as well as by the channel characteristic such

as available bandwidth, susceptibility of channel fading, antenna characteristics, ability

to transmit D.C or low frequencies etc. The last criterion is necessary when data

transmission using a telephone channel is intended, because of transformer or series

capacitors getting included in the transmission path. EX-FSK is very useful in a fading

channel because it is relatively insensitive to amplitude function. A fading channel is

one in which the received signal amplitude varies with the time because of variability’s

in the transmission medium

AMPLITUDE SHIFT KEYING

The simplest method of modulating a carrier with a data stream is to change

the amplitude of the carrier wave every time the data changes. This modulation

technique is known as Amplitude Shift Keying.

The simplest way of achieving amplitude shift keying is by switching 'ON' the

carrier whenever the data bit is '1' & switching 'OFF' whenever the data bit is '0 i.e. the

transmitter outputs the carrier for a ' 1 ' & totally suppresses the carrier for a '0'. This

technique is known as ON-OFF keying. Fig 11 illustrates the amplitude shift keying for

the given data stream. Thus

DATA = 1 CARRIER TRANSMITTED

DATA = 0 CARRIER SUPPRESSED

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The ASK waveform is generated by a balanced modulator circuit, also known

as a linear multiplier. As the name suggests, the device multiplies the instantaneous

signal at its two inputs.

The output voltage is being the product of the two input voltages at any

instance of time. One of the inputs is A.C Coupled 'carrier' wave of high frequency.

Generally, the carrier wave is a sine wave since any other waveform would increase

the Bandwidth, without providing any advantages. The other input which the

information signals to be transmitted is D.C coupled. It is known as modulating signal

carrier input & the digital data stream at modulation input.

STEP BY STEP PROCEDURE (ASK):

1. Patch the circuit as shown in the wiring diagram and switch on the trainer

2. To study modulation/demodulation set the Mode selection switches in the

corresponding positions.

MODE SELECTION:

Mode selection is used to select the modulation type. This is selected as follows.

Select Mode selector switches is as

S1 S2 S3 S4

X 0 0 0

X

Note:

After each operation depress reset switch.

Example:

If you need to change ASK modulation to FSK modulation, then change the mode

selector as ‘X 0 0 1’ and then press RESET switch.

3. Now select the data stream as mentioned above.

Dip switches are used to select the data and modes. If the switch position is

upward ‘ ‘then logic ‘1’ is given.


Don’t give any external voltage to microcontroller. It may affect the micro

controller ports.

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4. Now controller is working in the ASK modulation/demodulation mode.

5. Micro Controller port P2.5 - ASK modulation.

6. The o/p is connected from microcontroller to ASKMOD terminal

ASK DEMODULATION:

7. ASK modulation is given to ASK demodulation I/P.

8. This is given to demodulator controller input. Now controller gives the ASK

demodulated O/P through ASK demodulation test point.

Micro Controller PIN output configuration:

ASK demodulation-IN – P1.5 & OUT –P 2.5

CONCLUSION:

Whenever the data bit is ’1’, the carrier is switched on & whenever the data bit is ‘0’

the carrier is switched off i.e. the transmitter outputs the carrier for a ‘1’ & totally

suppresses the carrier for a ‘0’.

ASK SIMULATED OUTPUT

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WIRING DIAGRAM

ASK MODEM

.

INDICATES PATCHING CONNECTION

LAB ElectronicsMODEL-X31 MADE IN INDIA

POWER CARRIER GENERATOR MICROCONTROLLER SECTION

FSK MODEMASK MODEM PSK MODEM QPSK MODEM

DATA SELECTOR

DATA FORMATTING

MODE SELECTOR

DIGITAL COMMUNICATION TRAINER - 2

FREQ.CTRL+5V +12V

-12V-5V

AMP.CTRL

FSK

O/P

ASK

O/P

DEMOD

O/P

PSK

O/P

ODD BITS

MULTIPLIERMULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

SUMMER

EVEN BITS

PSK

I/P

QPSK

O/P

QPSK

I/P

DEMOD

O/P

DEMOD

O/P

MUX

DE

MOD

O/P

ASK

FSK

PSK

QPSK

NRZ

RZ

MANCHESTER

NRZ RZ MANCHESTER

GNDCOSSINE

12MHzCRYSTAL

12MHzCRYSTAL

+

+

+

+

NOT

X

X

XX

X

X

X

X

X

X

X

1

S

1

S

1 if z>0

0 if z<0

ODD BITS

EVEN BITS

440 878

2.637K

1K1K

1K

1K

2.6

37

K

1nf

1nf

+

+

+

+

+

-

-

-

-

-

SELLEN KEY FILTER

SELLEN KEY FILTER

SELLEN KEY FILTER

DEMOD

CIRCUIT

DATA

O/P

MODULATOR

DEMODULATOR

RESET

072TL

072TL072TL

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EXPERIMENT - 3

FSK MODULATION AND DEMODULATION

OBJECTIVE:

To study the Frequency Shift Keying (FSK) Modulation and Demodulation.

MATERIALS REQUIRED:

1. LAB DATA COMMUNICATION Trainer.


3. Oscilloscope.

FSK MODULATION:

In FSK signal the low frequency represents data 0 and the high frequency

represents data 1. The Frequency Shift Keying (FSK) scheme is used in new

commercial DIGITAL COMMUNICATION. Because of its close behavior to the FM

modulation technique, FSK is replacing FM in the new digital based radio receivers

because of the benefits digital modulation has over analog ones, as we mentioned

previously. As in FM, the amplitude of the FSK modulated signal is constant, but it’s

the changes in the frequency that carries the signal information. .In our design we are

using Binary FSK, that uses two levels off frequencies, one is for transmitting a binary

1, the other is for transmitting binary 0.

In FSK the carrier frequency has been varied according the given input data,

i.e. If data is 1 then the carrier gets high frequency. If data is 0 then the carrier gets

low frequency. In this FSK modem carrier is generated internally and modulated

output is observed as pulses.

If the given data is 1, then the frequency of the generated pulses has high

frequency that is more number of pulses in a particular period of time. If the given data

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is 0 then the frequency of the generated pulses has low frequency that is less number

of pulses in a particular period of time

STEP BY STEP PROCEDURE (FSK):

1. Patch the circuit as shown in the wiring diagram for Frequency shift keying on the

front panel of the trainer.

2. Set the Mode selection switches in the proper position depending up on the

Modulation experiment which you are going to study.

MODE SELECTION:


When mode selected switch is in on condition, the corresponding LED glows.

S1 S2 S3 S4

X

X 0 0 1

Note: Every time-reset switch should be pressed, after changing the mode.

Example:

Change the mode selector as ‘X001’ and then press RESET switch.

3. Now set the data selection in the proper position according to the input data

stream.

DATA SELECTION:

8-Bit Data selector is used to give the data to the controller.

S1 S2 S3 S4 S5 S6 S7 S8

D7 D6 D5 D4 D3 D2 D1 D0

MSB LSB

Dip - switches are used to select the data and modes. If the switch position is



Now controller is working in the FSK modulation mode.

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Note:

‘X’-defined as don’t care, .i.e., which doesn’t affect the process.

Micro Controller port P2.4 gives the FSK modulation.

The o/p is connected from microcontroller to FSK terminal.

FSK DEMODULATION:

Connect the FSK modulated output to the FSK demodulated I/P.

This is given to demodulator controller input.

Now controller gives the FSK demodulated O/P through FSK demodulation test

point.

Micro controller PIN output configuration:

FSK modulation- P2.4 (modulator controller)

FSK demodulation (Demodulator controller) - IN - P1.4 & OUT P2.4

CONCLUSION: In FSK signal the low frequency represents data 0 and the high frequency represents

data 1.

DISCUSSION:

In FSK the carrier frequency has been varied according the given input data, i.e.

If data is 1 then the carrier gets high frequency

If data is 0 then the carrier gets low frequency

In this FSK modem, the carrier is generated internally and modulated output is

observed as pulses.

If the given data is 1, then the frequency of the generated pulses has high

frequency that is more number of pulses in a particular period of time.

If the given data is 0 then the frequency of the generated pulses has low frequency

that is less number of pulses in a particular period of time

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FSK SIMULATED OUTPUT

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WIRING DIAGRAM

FSK MODEM

.

INDICATES PATCHING CONNECTION

LAB ElectronicsMODEL-X31 MADE IN INDIA



DATA SELECTOR

DATA FORMATTING

MODE SELECTOR

DIGITAL COMMUNICATION TRAINER - 2

FREQ.CTRL+5V +12V

-12V-5V

AMP.CTRL

FSK

O/P

ASK

O/P

DEMOD

O/P

PSK

O/P

ODD BITS


MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

SUMMER

EVEN BITS

PSK

I/P

QPSK

O/P

QPSK

I/P

DEMOD

O/P

DEMOD

O/P

MUX

DE

MOD

O/P

ASK

FSK

PSK

QPSK

NRZ

RZ

MANCHESTER

NRZ RZ MANCHESTER

GNDCOSSINE

12MHzCRYSTAL

12MHzCRYSTAL

+

+

+

+

NOT

X

X

XX

X

X

X

X

X

X

X

1

S

1

S

1 if z>0

0 if z<0

ODD BITS

EVEN BITS

440 878

2.637K

1K1K

1K

1K

2.6

37

K

1nf

1nf

+

+

+

+

+

-

-

-

-

-

SELLEN KEY FILTER

SELLEN KEY FILTER

SELLEN KEY FILTER

DEMOD

CIRCUIT

DATA

O/P

MODULATOR

DEMODULATOR

RESET

072TL

072TL072TL

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EXPERIMENT - 4

PSK MODULATION AND DEMODULATION

OBJECTIVE:

To study the Phase Shift Keying Modulation and Demodulation.

MATERIALS REQUIRED:

1. LAB DATA COMMUNICATION Trainer, Model x-31.


3. Oscilloscope.

PHASE SHIFT KEYING (PSK):

In this technique, the phase of the carrier frequency is varied in accordance

with the data stream.

The selection of particular modulation method used is determined by the

application intended as well as by the channel characteristic such as available

bandwidth, susceptibility of channel fading, antenna characteristics, ability to transmit

D.C or low frequencies etc. The last criterion is necessary when data transmission

using a telephone channel is intended, because of transformer or series capacitors

getting included in the transmission path.

EX-FSK is very useful in a fading channel because it is relatively insensitive to

amplitude function. A fading channel is one in which the received signal amplitude

varies with the time because of variability’s in the transmission medium,

PSK SIGNAL CONSTELLATION

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PSK MODULATION The Phase Shift Keying (PSK) Digital Modulation scheme is also widely used in

modern communications, especially in satellite communications, where M-ary PSK

modulation techniques are used for their bandwidth efficiency. PSK is considered one

of the linear modulation techniques that has constant envelope. In the BPSK

modulation (Binary PSK, which is the one used here), the phase of the constant

amplitude signal is switched between two values according to two possible signals m1

and m2 corresponding to binary 1 and 0 respectively. Usually the phases are 1800

apart.

The equations of the two modulated signals are:

A block diagram of a BPSK system is shown in Figure below

Here the NRZ Encoder transforms the level of the binary input data into a +ve level for

the binary 1, and a -ve level for the binary 0 in order to change the carrier phases. The

average Probability of symbol error, or equivalently, the bit error rate for coherent

binary PSK is

PSK BLOCK DIAGRAM

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Here the Eb/No is double the one in its FSK counterpart, which means that we have to

double the Eb/No for the FSK signal in order to have the same average error rate as

the BPSK one. This is obvious when looking at the signal constellation of the BPSK

and the BFSK. The distance between the two binary points in the FSK constellation is

almost half the distance in the BPSK constellation, which means that the probability of

false decision in the FSK is double its PSK counter part. That’s why we need to

double the Eb/No for the FSK to compensate for and have the same average error

probability of its PSK counterpart. BPSK is considered bandwidth efficient and its

bandwidth efficiency in-creases with the increase of the number of bits per symbol,

this will affect its power efficiency. The channel band width required to pass M-ary

PSK signals is given by:

Where T is the symbol duration, Also using Rb = 1

The PSK bandwidth efficiency formula:

THE BANDWIDTH EFFICIENCY AND THE POWER EFFICIENCY OF THE M-LEVELS FOR

PSK MODULATION

We notice that the BPSK is more bandwidth efficient than its FSK counterpart, but

there is a trade off in its Power efficiency.

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PSK DEMODULATOR BLOCK DIAGRAM

As for the Demodulation process, for coherent detection, the basic demodulation

scheme is shown in Figure above

Here we have the incoming signal multiplied with a synchronized oscillator that has

the same frequency of the modulation frequency. These two are multi-plied together,

and the output is applied to a LPF (Low Pass Filter) to remove noise and to perform

integration on the incoming signal. The decision device follows giving the Binary

output.

PSK WAVEFORM:

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STEP BY STEP PROCEDURE (PSK):

1. Patch the circuit as shown in the wiring diagram for phase shift keying on the front

panel of the trainer.

2. OBSERVE the SINE INPUT to the phase shift keying circuit in the front panel of

the trainer.

Switch "ON" the trainer.

MODE SELECTION:


S1 S2 S3 S4

0 0 1 0


Example:

Change the mode selector as ‘0010’ and then press RESET switch. Now controller

is working in the PSK modulation mode.

4. Now set the data selection in the proper position according to the input data

stream.

DATA SELECTION:


S1 S2 S3 S4 S5 S6 S7 S8

D7 D6 D5 D4 D3 D2 D1 D0

MSB LSB

Dip - switches are used to select the data and modes. If the switch position is in



Now controller is working in the PSK modulation mode.

5. Micro Controller port P2.0&P2.1 gives data to the comparator for getting PSK

modulation.

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6. The o/p is connected to PSK MOD test point, Observe the PSK modulated output

in this test point

PSK DEMODULATION:

7. Connect PSK modulated output to PSK demodulation I/P.

The O/P of demodulation is given to demodulator controller input.

PSK demodulation- INPUT PORT - P1.0 & OUT- P2.3

8. Now controller gives the PSK demodulated O/P through PSK demodulation test

point.

CONCLUSION:

When logic level goes either from high to low or low to high the phase transitions will

be 1800.

SIMULATED OUTPUT

PSK MODULATED WAVEFORM

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LAB ELECTRONICS

PSK DEMODULATED WAVEFORM

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LAB ELECTRONICS

WIRING DIAGRAM

PSK MODEM

INDICATES PATCHING CONNECTIONS



DATA SELECTOR

DATA FORMATTING

MODE SELECTOR

FREQ.CTRL+5V +12V

-12V-5V

AMP.CTRL

FSK

O/P

ASK

O/P

DEMOD

O/P

PSK

O/P

ODD BITS


MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

SUMMER

EVEN BITS

PSK

I/P

QPSK

O/P

QPSK

I/P

DEMOD

O/P

DEMOD

O/P

MUX

DE

MOD

O/P

ASK

FSK

PSK

QPSK

NRZ

RZ

MANCHESTER

NRZ RZ MANCHESTER

GNDCOSSINE

12MHzCRYSTAL

12MHzCRYSTAL

+

+

+

+

NOT

X

X

XX

X

X

X

X

X

X

X

1

S

1

S

1 if z>0

0 if z<0

ODD BITS

EVEN BITS

440 878

2.637K

1K1K

1K

1K

2.6

37

K

1nf

1nf

+

+

+

+

+

-

-

-

-

-

SELLEN KEY FILTER

SELLEN KEY FILTER

SELLEN KEY FILTER

DEMOD

CIRCUIT

DATA

O/P

MODULATOR

DEMODULATOR

RESET

072TL

072TL072TL

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EXPERIMENT - 5

QPSK MODULATION AND DEMODULATION

OBJECTIVE:

To study the Quadrature Phase Shift Keying Modulation and Demodulation.

MATERIALS REQUIRED:

1. LAB DATA COMMUNICATION Trainer, Model X-31.


3. Oscilloscope.

QPSK MODULATION

The Quadrature Phase Shift Keying (QPSK) is a 4-ary PSK signal. The QPSK is a

modulation scheme widely used in Satellite Communications. As we mentioned

earlier, PSK signals are considered one of the linear modulation techniques, which are

well known of their bandwidth efficiency.

The phase of the carrier in the QPSK takes 1 of 4 equally spaced shifts, such as 0,

/2, , 3/2, where each value of phase corresponds to a unique pair of message bits.

The QPSK transmitted signal is defined by:

Another way of having a QPSK modulation is by using the phase

shifts./4.3/4.5/4.7/4.The QPSK modulator consists of two streams of PSK

modulators, one is fed with the Odd data sequence and the other with the even

sequence. Also one stream is modulated with a cos wave and the other with a sine

wave to have a /2 phase difference. As for the bandwidth and power efficiency

measures. The bandwidth efficiency of QPSK is twice that of PSK since we are

transmit-ting two bits per signal. The Average probability of bit error of the QPSK

signaling is

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THE TWO POSSIBLE QPSK SIGNAL CONSTELLATIONS

QPSK SIGNAL CONSTELLATION WITH ITS DECISION REGIONS

The Binary Dibit and its corresponding phase.

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QPSK MODULATOR BLOCK DIAGRAM

Surprisingly, the average probability of bit error of the QPSK is the same as that of the

PSK in AWGN channel4, while as much data can be sent in the same bandwidth.

Thus compared to PSK, QPSK provides twice the spectral efficiency with exactly the

same energy efficiency.

.

QPSK Demodulator Block diagram

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The input QPSK stream is applied to two sinusoidal modulators that are 90

apart. The outputs from the multipliers are then applied to two integrators that perform

both filtering and integration. After that the input is applied to a decision device that

determines the level received. The outputs from the decision devices are applied to a

multiplexer that performs parallel to serial data conversion, thus reconstructing the

final output data stream. In the circuit design section, this block diagram was satisfied

by substituting each of the blocks with a suitable circuit designed to perform its

function. The circuit gave impressive results. Figure below Illustrates an overall

graphical comparison for the Noise performance of the three schemes, the FSK, PSK,

and QPSK in AWGN:

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SINE AND COSINE WAVEFORM

QPSK WAVEFORM:

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LAB ELECTRONICS

SIMULATED OUTPUT

DATA ODD/EVEN

.

DATA

ODD

EVEN

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LAB ELECTRONICS

STEP BY STEP PROCEDURE (QPSK):

1. Patch the circuit as shown in the wiring diagram for quadrature phase shift keying

in the front panel of the trainer.

Switch "ON" the trainer and set the Mode selection switches in the proper position.

MODE SELECTION:


S1 S2 S3 S4

1 0 1 1


Example:

Change the mode selector as ‘1011’ and then press RESET switch.

Now set the data selection in the proper position according to the input data

stream.

DATA SELECTION:


S1 S2 S3 S4 S5 S6 S7 S8

D7 D6 D5 D4 D3 D2 D1 D0

MSB LSB

D6 D4 D2 D0 ----------- ODD DATA

D7 D5 D3 D1 ---------- EVEN DATA

Dip - switches are used to select the data and modes. If the switch position is

upward ‘ ‘ then logic ‘1’ is given.

If dip switch is in downward position ‘ ‘ then logic ‘0’ is given.

Now the controller is working in the QPSK modulation mode.

Port P2.3 & P2.2 are given to EVEN bit generating comparator and port P2.1 &

P2.0 are given to ODD bit generating comparator.

The o/p is connected from QPSK MOD test point.

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Connect SINE OUTPUT and COSINE OUTPUT from carrier generator section

to the QPSK modulation section.

Data odd and even are internally connected.

Finally observe the QPSK output at the corresponding test point.

QPSK DEMODULATION:

QPSK modulation is given to QPSK demodulation I/P.

This is given to demodulator controller input.

Now controller gives the QPSK demodulated O/P through QPSK demodulation

test point.

QPSK demodulation-IN- P1.0, P1.1& OUT- P2.2 Due to lower carrier frequency

you cannot observe the actual output for QPSK.

Vary the data switches and observe the corresponding demodulated output.

CONCLUSION:

In QPSK the carrier phase can change only once every 2T secs. If from one T interval

to the next one, neither bit stream changes sign, the carrier phase remains

unchanged. If one component aI(t) or aQ(t) changes sign, a phase change of /2

occurs. However if both components change sign then phase shift of occurs

QPSK MODULATED WAVEFORM

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LAB ELECTRONICS

WIRING DIAGRAM

QPSK MODEM



DATA SELECTOR

DATA FORMATTING

MODE SELECTOR

FREQ.CTRL+5V +12V

-12V-5V

AMP.CTRL

FSK

O/P

ASK

O/P

DEMOD

O/P

PSK

O/P

ODD BITS


MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIP LIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

MULTIPLIER

SUMMER

EVEN BITS

PSK

I/P

QPSK

O/P

QPSK

I/P

DEMOD

O/P

DEMOD

O/P

MUX

DE

MOD

O/P

ASK

FSK

PSK

QPSK

NRZ

RZ

MANCHESTER

NRZ RZ MANCHESTER

GNDCOSSINE

12MHz

CRYSTAL

12MHz

CRYSTAL

+

+

+

+

NOT

X

X

XX

X

X

X

X

X

X

X

1

S

1

S

1 if z>0

0 if z<0

ODD BITS

EVEN BITS

440 878

2.637K

1K1K

1K

1K

2.6

37K

1nf

1nf

+

+

+

+

+

-

-

-

-

-

SEL LEN KEY

FILTER

SEL LEN KEY

F ILTER

SEL LEN KEY

F ILTER

DEMODCIRCUIT

DATA O/P

MODULATOR

DEMODULATOR

RESET

072TL

072TL072TL

INDICATES PATCHING CONNECTIONS

DATA COMMUNICATION TRAINER

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