QPSK

QPSK and DQPSK Modulation/Demodulation

Exercise 1 Assigning the oscillograms at the test points DATA and DIBIT-CLOCK, to a set bit pattern

Note:

Before commencing the exercise, check the alignment of the PSK modulator,

SO4201-9J, in accordance with the operating instructions!

On the PSK / QPSK modulator (SO4201-9J), connect the "Sync" output to the

analog test input (channel B) of the UniTr@in-Interface. On channel A measure the

signal at the "Data" output. Trigger on B. For more stable triggering, set the trigger

point to 50% of the amplitude of the squarewave signal.

Set the following bit pattern (Byte) on the DIP switches:

Set the switch for the modulation type to "4PSK", the jumper for the transfer rate to

"1200" and by pressing the "SET" button, read in the bit pattern.

Caution:

The "Set" button must be pressed again, after each new change of the settings has

been completed!

On an oscilloscope, display the voltages at the test points DATA, BITCLOCK and

DIBITCLOCK. What is the sequence of the bits during transfer? How many bits are

transferred for each bit-clock and Dibit-clock ?

Result:

MTI 7604 PSK / QPSK Modulation and Demodulation

LSB

Bit 1

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

MSB

Bit 8

0 1 1 1 1 0 0 0

X = 1 ms/DIVX/T

(B)

Chan.

A=2 V/DIV DC

Chan.

B=2 V/DIV DC

MTI 7604

Page 1 of 8Name: securistu, Date: 5/12/2015

Fig. 1: Data signal

Fig. 2: Bit-clock

X = 1 ms/DIVX/T

(B)

Kannal

A=2 V/DIV DC

Kannal

B=2 V/DIV DC

X = 1 ms/DIVX/T

(B)

Chan.

A=2 V/DIV DC

Chan.

B=2 V/DIV DC

MTI 7604


Fig. 3: Dibit-clock

?

?

?

?

Exercise 2 Displaying the dependency of the DIBIT X and DIBIT Y signals on the associated Dibits of the selected bit pattern

On an oscilloscope, display the signals at the test points "DIBIT X" and "DIBIT Y"

as a function of the bit pattern selected.

Result:

X = 1 ms/DIVX/T

(B)

Chan.

A=2 V/DIV DC

Chan.

B=2 V/DIV DC

MTI 7604


Fig. 4: Dibit formation; Dibit X

Fig. 5: Dibit formation; Dibit Y

Exercise 3 Assigning the output voltage QPSK to various bit patterns or Dibits

Determine the phase relationship of the QPSK signal and the set DATA signal (the

Dibits in the signal). For this, compare the phase of the QPSK signal with the

X = 1 ms/DIVX/T

(B)

Chan.

A=2 V/DIV DC

Chan.

B=2 V/DIV DC

DIBIT 00 01 10 11

DIBIT X ??? ??? ??? ???

DIBIT Y ??? ??? ??? ???

MTI 7604


signals at the test points T (0, 90, 180, 270). Bear in mind that the QPSK signal

compared to the reference signals, exhibits a small but recognisable delay caused

by the transit time.

Result:

Fig. 6: Phase relationship of the Dibits in a QPSK

In the Fig. 6 from oscilloscope was transmitted a QPSK-Signal. Write the original

code beginning by the MSB in the table below. Then write the code, if it was

transmitted a DQPSK-Signal.

Result:

Exercise 4 Effect of various rates of transfer

Determine the baud rate vS, data transfer rate vD and the number of bytes

transferred per second (cps) for the "600" and "1200" transfer rate settings.

Compare the appearance of the 4PSK signal at either setting.

X = 1 ms/DIVX/T

(B)

Chan.

A=0,5 V/DIV DC

Chan.

B=2 V/DIV DC

DIBIT 00 01 10 11

Phase relationship QPSK ??? ??? ??? ???

Phase shift in DQPSK signal ??? ??? ??? ???

MSB

Bit 8

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

LSB

Bit 1

QPSK ??? ??? ??? ??? ??? ??? ??? ???

DQPSK ??? ??? ??? ??? ??? ??? ??? ???

MTI 7604


Note:

For determining the transfer rate, use the time marker on the oscilloscope!

In the lower part of the operating bar for the oscilloscope, the button will be seen for

the cursor function. Set this for channel A. Also, two amplitude markers are

available for measuring voltages and two time markers for measuring time or

frequency.

The marker can be moved with the mouse to the position required. The values

detected are shown at the top right.

Result ("600"position)

Fig. 7: 4PSK signal at 600 Bd

?

?

?

?

Result ("1200" position ):

X = 0,5 ms/DIVX/T

(B)

Chan.

A=0,5 V/DIV DC

Chan.

B=2 V/DIV DC

X = 1 ms/DIVX/T

(B)

Chan.

A=0,5 V/DIV DC

Chan.

B=2 V/DIV DC

MTI 7604


Fig. 8: 4PSK signal at 1200 Bd

?

?

?

?

Exercise 5 Demodulation of the QPSK signal

Without changing the setting of the modulation, connect the "(Q)PSK" and "Car."

outputs of the QPSK / PSK modulator to the corresponding inputs on the QPSK /

PSK demodulator (SO4201-9K).

For synchronising, the carrier signal (CAR) must be transferred with the output

signal.

Set the demodulator according to the conditions for receiving modulated data:

- Transfer rate switch: Position "1200",

- Type of modulation switch: Position "4PSK"

On the PSK / QPSK modulator (SO4201-9J), connect the "Sync" output to the

analog test input, channel B, of the UniTr@in-Interface. On channel A, measure the

signal at the "Data" output of the QPSK / PSK demodulator (SO4201-9K). Trigger

on B. For more stable triggering, set the trigger point to 50% of the amplitude of the

squarewave signal.

Result:

X = 1 ms/DIVX/T

(B)

MTI 7604


Fig. 9: 4PSK demodulation

?

?

?

?

Set other different bit patterns with the DIP switches and change the data transfer

rate (modulator and demodulator settings must be the same).

Chan.

A=2 V/DIV DC

Chan.

B=2 V/DIV DC

MTI 7604


Documents

QPSK