20-07-2013, 02:43 PM
QPSK MODULATION AND DEMODULATION
AIM:
To generate a QPSK for a given binary digital signal and Observe. Demodulate the same QPSK to get back
the
Original digital signal, using carrier receiving circuit and Demodulator
COMPONENTS REQUIRED:
Patch chords , signal generator, CRO, probes.
THEORY:
The figure shows the block diagram of a QPSK system. The input binary sequence is converted to binary
NRZ Type of signal. This signal is called b (t). “1” is represented By +1v and “0” is represented by –1v.
The demultiplexer Divides b (t) into two separate bit streams of odd numbered And even numbered bits.
The even bit stream modulates Ps sin 2fot carrier and bo (t) modulates ps cos. 2fot.
PROCEDURE:
1) Refer to the block diagram & carry out the following connections and switch settings
2) Connect power supply in proper polarity to the kit.
3) Select data pattern of simulated data using switch SW1
4) Connect SDATA generated in DATA IN to NRZ-L CODER.
5) Connect the coded data NRZ-L DATA to the DATA IN of the DIBIT CONVERSION
6) Connect SCLOCK to CLK IN of DIBIT CONVERSION
7) Connect the dibit data I bit to control input C1 of CARRIER MODULATION
8) Connect the dibit data Q bit to control input C2 of CARRIER MODULATION
9) Connect the carrier component to input of CARRIER MODULATOR as follows