1. CHAPTER - 6 Introduction to Communication Systems (222 CNET - 3)
RADIO COMMUNICATIONS
1440H- First Semester
Mohammed Rizwan Shaik

2. Chapter Contents Radio Communications 6.1 Introduction
6.2 Radio Transmitters : AM & FM
6.3 Radio Receivers : TRF and Super-heterodyne
6.4 Receivers : Sensitivity and Selectivity

3. Objectives of this chapter
Upon completion of this chapter student will be able to
Explain the block diagram of Radio Communication System.
Describe types of Transmitter and Receiver.
Define Sensitivity and Selectivity.

4. Introduction Radio Communication:
In Radio Communication, the message transmission takes place in
Radio Frequency(RF) range.
The three important blocks of Communication System
Transmitter
Channel
Receiver
Radio is the technology of using radio waves to carry information, such as sound, by systematically modulating properties of electromagnetic energy waves transmitted through space, such as amplitude, frequency, phase, or pulse width.

5. Radio Communication System

6. Description of Blocks
Radio Transmitter : This block collects the incoming messages and modifies it to suitable fashion so that it can be transmitted via the chosen channel to the receiver.
Radio Receiver : This block will do the reverse operation of a transmitter to recover the message from the received weak signal.
Channel : The channel is the physical medium that connects the transmitter and receiver blocks.

7. Uses of Radio Waves 1. Fixed and Mobile Radio Communication
2. Broadcasting Radio
3. Radar Communication
4. Navigation

8. Categories of Radio Communication system
Radio Transmitter
Radio Receiver
Radio Transmitter is divided into two categories such as
1. AM Transmitter
2. FM Transmitter
Radio Receiver is divided into two categories such as
1. Tuned Radio Frequency
2. Super-Heterodyne

9. Radio Transmitter
Radio Transmitter is an electronic system that accepts the incoming message and converts it into a modulated signal in the RF range by the modulation process.
Blocks of Radio Transmitter:
1. Oscillator
2. Modulator
3. Power Amplifier
4. Antenna

10. Block Diagram of Radio Transmitter
Block diagram of AM Transmitter
Power Supply
Oscillator
Modulator
Amplifier
Audio/video

11. AM Transmitter

12. Explanation AM transmitter operates on two level modulation
1. High Level Modulation
2. Low Level Modulation
High Level Modulation
Low Level Modulation
High Power Modulation
Low Power Modulation
Efficiency is more
Simplicity is more
High Cost
Low Cost
High Quality
Low Quality
Half of the carrier power
Power level of milli watts

13. FM Transmitter

14. Explanation
FM Transmitter is classified as Low level and High level transmitters.
Crystal Oscillator : It generates the stable carrier signal then both modulating signal and carrier signal is applied to the phase modulator.
Phase Modulator : Operating in the Low power level to generate a narrowband FM wave.
Frequency Multiplier : To increase the frequency deviation and also carrier signal frequency to the required level. The several stages of frequency multiplications helps in choosing a suitable combination of required level of multiplication factors needed for deviation and carrier signal frequency.
The output of frequency multipliers stage will be wideband FM but at the low power level.
Power Amplifier: The WBFM is then passed through one or more stages of power amplifiers to add required power levels. The WBFM with high power is then finally transmitted via the antenna towards the receiver.

15. Radio Receiver

16. Receiver Types There are two kinds of radio receiver:
Tuned Radio Frequency Receiver(TRF)
Super Heterodyne Receiver

17. Tuned Radio Frequency(TRF)

18. Super Heterodyne Block diagram

19. Explanation

20. Advantages of Super Heterodyne

21. Advantages of AM Receiver

22. Sensitivity & Selectivity

23. Graph of Sensitivity & Selectivity

24. FM Receiver FM Receiver is a Super Heterodyne receiver.
The basic differences between AM & FM are as follows.

25. Thank You