Generation of Radio wave

   

In the previous chapter we learnt about radio waves characteristics and applications, in this chapter we shall learn about how radio waves are generated, while in the next chapter we will also try to build an homemade radio station which can transmit signal over 1000 km. 

Let's get started! Radio waves are radiated by charged particles when they are accelerated. They are produced by time-varying electric currents, consisting of electrons flowing back and forth in a specially-shaped metal conductor called an antenna.  

An electronic device called a radio transmitter applies an high frequency oscillating electric current to the antenna, and the antenna radiates the power as radio waves. Radio waves are received by another antenna attached to a radio receiver. When radio waves strike the receiving antenna they push the electrons in the metal back and forth, creating tiny oscillating currents which are detected by the receiver. 

 

From quantum mechanics, like other electromagnetic radiation such as light, radio waves can alternatively be regarded as streams of uncharged elementary particles called photons. In an antenna transmitting radio waves, the electrons in the antenna emit the energy in discrete packets called radio photons, while in a receiving antenna the electrons absorb the energy as radio photons. 

Basic parts of radio communication.

To transmit signals or information, there are two parts namely, transmitter and receiver. The transmitter is use to generate radio wave and modulate information and signals along it and then transmitted.

The reciever uses an antenna to receive the radio wave from the transmitter and then demodulate  it into useful information.

1. Transmitter. 

 

The radio transmitter consists of an oscilator, antenna, modulator, power supply and an amplifier to generate radio waves that transmit useful information such as vedio signals, audio signals or even digital data.

•Power supply.

It provides the required amount of power to operate the transmitter.

•Oscillator.

It is a circuit that is use to create alternating current at the frequency on which the transmitter will transmit. The oscillator usually generates a sine wave, which is referred to as a carrier wave.

•Modulator.

It is a circuit which modulates or add useful information to the carrier wave. There are two techniques  to modulate information into carrier wave, they are mainly; amplitude modulation(AM) and Frequency modulation (FM).

The amplitude modulation technique makes slight increases or decreases to the intensity of the carrier wave. While the  Frequency modulation(FM) method makes slight increase or decrease in the frequency of the carrier wave.

•Amplifier.

The amplifier circuit is use to amplify the modulated carrier wave to increase its power. The more powerful the amplifier, the more powerful the broadcast. .

 

•Antenna.

It's a metal rod which is use to convert the  amplified modulated signals into radio wave.

2. Receiver.

A radio receiver is the opposite of a radio transmitter. It uses an antenna to capture radio waves, processes those waves to extract only those waves that are vibrating at the desired frequency, extracts the audio signals that were added to those waves, amplifies the audio signals, and finally plays them on a speaker. 

•Antenna. 

Captures the radio waves. Typically, the antenna is simply a length of wire. When this wire is exposed to radio waves, the waves induce a very small alternating current in the antenna. 

•RF amplifier.

A sensitive amplifier that amplifies the very weak radio frequency (RF) signal from the antenna so that the signal can be processed by the tuner. 

•Tuner. 

A circuit that can extract signals of a particular frequency from a mix of signals of different frequencies. On its own, the antenna captures radio waves of all frequencies and sends them to the RF amplifier, which dutifully amplifies them all. Unless you want to listen to every radio channel at the same time, you need a circuit that can pick out just the signals for the channel you want to hear. That’s the role of the tuner. The tuner usually employs the combination of an inductor (for example, a coil) and a capacitor to form a circuit that resonates at a particular frequency. This frequency, called the resonant frequency, is determined by the values chosen for the coil and the capacitor. This type of circuit tends to block any AC signals at a frequency above or below the resonant frequency. You can adjust the resonant frequency by varying the amount of inductance in the coil or the capacitance of the capacitor. In simple radio receiver circuits, the tuning is adjusted by varying the number of turns of wire in the coil. More sophisticated tuners use a variable capacitor (also called a tuning capacitor) to vary the frequency.

•Detector.

Responsible for separating the audio information from the carrier wave. For AM signals, this can be done with a diode that just rectifies the alternating current signal. What’s left after the diode has its way with the alternating current signal is a direct current signal that can be fed to an audio amplifier circuit. For FM signals, the detector circuit is a little more complicated.

•Audio amplifier.

This component’s job is to amplify the weak signal that comes from the detector so that it can be heard. This can be done using a simple transistor amplifier circuit.