Types of Conversions Cont

™   Frequency Shift Keying (FSK) o    Frequency of signal is varied to represent binary 1 or 0 o    The frequency of the signal during each bit duration is constant and depends on the bit (0 or 1) o    Both peak amplitude and phase remains constant ƒ     Effect of Noise on FSK o    Avoids most of the Noise problems of ASK o    Because  Rx  device  is  looking  for  specific  frequency  changes  over  a  given number of periods, it can ignore voltage spikes o    The limiting factors of FSK are the physical capabilities of the carrier    BW of FSK

o    Although FSK shifts between two carrier frequencies, it is easier to analyze as two co-existing frequencies o    BW  required  for  FSK  is  equal  to  the  Baud  rate  of  the  signal  plus  the  frequency shift o    Frequency Shift=Difference b/w two carrier frequencies o    BW= (fc1 - fc0) +Nbaud Example 5.11 Find the minimum BW for an FSK signal transmitted at 2000 bps. TX is in half duplex mode and carrier must be separated by 3000 Hz Solution: For FSK, if fc1 and fc2 are the carrier frequencies, then: BW=Baud Rate + (fc1 - fc0) Baud rate is the same as bit rate BW=2000 + (fc1 - fc0) = 2000 + 3000 = 5000 Hz