### Frequency Shift keying:-

In a Binary FSK system , Symbols ‘1’ and ‘0’ are distinguished from each other by transmitting one of two sinusoidal waves that differ in frequency by a fixed amount. (or) the frequency of the carrier signal is shifted to two frequencies f_{c1} (or)f_{H} and f_{c2}/f_{L} for symbols ‘1’ and ‘0’ transmission.

The equation for FSK signal is

and i= 1,2.

where is generally a high-frequency, is a low-frequency. Vice-versa is also true.

where and

### FSK wave forms:-

### FSK/BFSK Generator :-

The input to the FSK generator is a binary sequence 1 0 1 0 …..etc.

- FSK generator uses two product modulators upper modulator and lower modulator with carriers and
- A level shifter is there in which the output of level-shifter is volts when the input is a binary ‘1’ and ‘0’ volts for the input ‘0’.

**Input to the level shifter****output of the level shifter**‘1’ ‘0’ 0 - The working of FSK generator is as follows, when input binary sequence ‘1’ on the upper modulator 1 has been shifted to a voltage so that the output of product modulator 1 is

and on the lower modulator input is ‘1’ is passed through an inverter and the output of inverter is ‘0’ then the output of level shifter will not change it remains at ‘0’ volts itself, then the output of the second product modulator is

∴ the over all output

since

.

similarly, when the input sequence is a binary ‘0’ , intermediate outputs at the product modulators and .

∴ the over all output which is the required output for binary ‘0’ transmission.