Explain frequency modulation.

Modulation is the process by which information is encoded from a message source in order to optimise it for transmission. Frequency Modulation (FM) is the encoding of information in a carrier wave by changing the instantaneous frequency of the wave. FM technology is widely used in the fields of computing, telecommunications, and signal processing. There are several methods that can be used to generate either direct or indirect frequency-modulated signals. 1) A voltage-controlled oscillator or a Varactor diode oscillator :- A voltage-controlled oscillator can be used to form Direct FM modulation by directly feeding the message into the input of the oscillator. In the case of the varactor diode, we place this device within the tuned circuit of an oscillator circuit. 2) Crystal oscillator circuit :- Varactor diode can also be used within a crystal oscillator circuit wherein the signal needs to be multiplied in frequency, and only narrowband FM is attained. 3) Phase locked loop :- This is an excellent method to generate frequency modulation signals. However, the constraints within the loop should be checked carefully and once everything is stable it offers an excellent solution.

Which type of communication is employed in mobile phones?

The space wave propagation is employed in mobile phones, then; Space wave propagation: This transmission is limited to the line of sight. Waves generally travel in a straight line from the transmitter to the receiver. It is used for propagation of waves of frequency greater than 40 MHz . The ground wave propagation is not used for low range, it is used in landlines. And in the case of sky wave propagation the frequency is more than instead of reflection, refraction takes place and the waves are not received by the receiver.