2. Electromagnetic Waves

Electromagnetic Waves

Propagation of Electromagnetic Waves

Various propagation modes for em waves are shown in the figure given below

Ground wave propagation

Radio waves traveling through atmosphere and moving along the surface of the earth are termed as ground waves. Ground wave propagation is suitable for low frequencies (500 kHz to 1500kHz) or for radio broadcast at long wavelength i.e., upto 1 MHz.

Sky wave propagation

The frequency range from a few MHz up to 30 to 40 MHz, long distance communication can be achieved by ionospheric reflection.

​MODULATION AND ITS NECESSITY

Transmission of information by communication systems over large distances is quite a feat of human ingenuity. We can talk, video chat and text anyone on this planet! The communication system uses a very clever technique called Modulation .

Types of Modulation

1.Amplitude Modulation

2.Frequency Modulation

3.Phase Modulation

AMPLITUDE MODULATION

In AM, the voltage or power level of the information signal changes the amplitude of the carrier in proportion. With no modulation, the AM carrier is transmitted by itself.

PRODUCTION OF AMPLITUDE MODULATED WAVE

DETECTION OF AMPLITUDE MODULATED WAVE

The transmitted message gets attenuated in propagating through the Channel. The receiving antenna is therefore to be followed by an amplifier And a detector. In addition, to facilitate further processing, the carrier Frequency is usually changed to a lower frequency by what is called an

Intermediate frequency (IF) stage preceding the detection.