Frequency Shift Keying (FSK) - Digital To Analog Conversion and Transmission Tutorials Part III
http://ingenuitydias.blogspot.com/2014/04/frequency-shift-keying-fsk-digital-to.html
The digital data stream changes the frequency of the carrier signal, fc.
For example, a “1” could be represented by f1=fc +Df, and a “0” could be represented by f2=fc-Df.
Binary frequency shift keying
Bandwidth of FSK
If the difference between the two frequencies (f1 and f2) is 2Df, then the required BW B will be:
B = (1+d)xS +2Df
Problem Example - 1
We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What should be the carrier frequency and the bit rate if we modulated our data by using FSK with d = 1?
Solution
This problem is similar to Example 5.3, but we are modulating by using FSK. The midpoint of the band is at 250 kHz. We choose 2Δf to be 50 kHz; this means
Coherent and Non Coherent FSK scheme
In a non-coherent FSK scheme, when we change from one frequency to the other, we do not adhere to the current phase of the signal.
In coherent FSK, the switch from one frequency signal to the other only occurs at the same phase in the signal.
Multi level FSK
Similarly to ASK, FSK can use multiple bits per signal element.
That means we need to provision for multiple frequencies, each one to represent a group of data bits.
The bandwidth for FSK can be higher
B = (1+d)xS + (L-1)/2Df = LxS
Bandwidth of MFSK used in Problem Example-1
Problem Example-2
We need to send data 3 bits at a time at a bit rate of 3 Mbps. The carrier frequency is 10 MHz. Calculate the number of levels (different frequencies), the baud rate, and the bandwidth.
For example, a “1” could be represented by f1=fc +Df, and a “0” could be represented by f2=fc-Df.
Further Reading suggested :
Bandwidth of FSK
If the difference between the two frequencies (f1 and f2) is 2Df, then the required BW B will be:
B = (1+d)xS +2Df
Problem Example - 1
We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What should be the carrier frequency and the bit rate if we modulated our data by using FSK with d = 1?
Solution
This problem is similar to Example 5.3, but we are modulating by using FSK. The midpoint of the band is at 250 kHz. We choose 2Δf to be 50 kHz; this means
Coherent and Non Coherent FSK scheme
In a non-coherent FSK scheme, when we change from one frequency to the other, we do not adhere to the current phase of the signal.
In coherent FSK, the switch from one frequency signal to the other only occurs at the same phase in the signal.
Multi level FSK
Similarly to ASK, FSK can use multiple bits per signal element.
That means we need to provision for multiple frequencies, each one to represent a group of data bits.
The bandwidth for FSK can be higher
B = (1+d)xS + (L-1)/2Df = LxS
Bandwidth of MFSK used in Problem Example-1
Problem Example-2
We need to send data 3 bits at a time at a bit rate of 3 Mbps. The carrier frequency is 10 MHz. Calculate the number of levels (different frequencies), the baud rate, and the bandwidth.