CSE JRF A & T

• 1 CARRIER FREQUENCIES ARE USED IN BASK (BINARY AMPLITUDE SHIFT KEYING)  

• 2 CARRIER FREQUENCIES ARE USED IN BFSK (BINARY FREQUENCY SHIFT KEYING)  

• 1 CARRIER FREQUENCIES ARE USED IN BPSK (BINARY PHASE SHIFT KEYING)  

 BASK

 THE DIGITAL DATA TO BE TRANSMITTED IS THE BINARY NUMBER 1011. TWO AMPLITUDES ARE USED TO DIRECTLY REPRESENT THE DATA, EITHER 0 OR 1. IN THIS CASE, THE MODULATION IS CALLED BINARY AMPLITUDE SHIFT KEYING OR BASK. THE SIGNAL IS DIVIDED INTO FOUR PULSES OF EQUAL DURATION WHICH REPRESENT THE BITS IN THE DIGITAL DATA. THE NUMBER OF BITS USED FOR EACH CHARACTER IS A FUNCTION OF THE SYSTEM, BUT IS TYPICALLY EIGHT, SEVEN OF WHICH REPRESENT THE 128 POSSIBLE CHARACTERS, THE LAST BIT IS USED TO CHECK FOR ERRORS, AND IS EXPLAINED AT THE END OF THIS CHAPTER.

BFSK

 IN FREQUENCY SHIFT KEYING, THE CARRIER FREQUENCY IS CHANGED BETWEEN DISCRETE VALUES. IF ONLY TWO FREQUENCIES ARE USED THEN THIS WILL BE CALLED BFSK, FOR BINARY FREQUENCY SHIFT KEYING. IN THIS FIGURE, THE SAME DATA IS REPRESENTED, 1011.

BPSK

 The phase of the carrier wave at the beginning of the pulse is changed between discrete values. This particular case is the same code shown above but in BPSK.