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o i d a s r R e t t i m s n a r T T Srinivasa Rao Communication Systems (EC-326) 1

EC 326 COMMUNICATION SYSTEMS UNIT – I Part I T Srinivasa Rao Dept. of ECE Bapatla Engineering College

Part 1 • RADIO TRANSMITTERS: • Frequency allocation for radio communication systems. • Block diagrams and functions of radio transmitters for AM and FM systems. T Srinivasa Rao Communication Systems (EC-326) 3

Types of Communication A B Simplex – A can talk to B • • Radio, T. V. broadcasting, CD/DVD ROM Simplest type, requires one transmitter and one receiver A B Duplex - A and B both can talk to each other simultaneously • • • Telephone, Telegraph Complex, requires two transmitter and two receiver at both ends Needs two different channels for simultaneous transmission A • • • B Half-Duplex – A and B can both talk to each other but not simultaneously Fax, CD/DVD RW Needs one single channel for transmission Compromise between two, don’t require separate transmitter and receiver Same antenna and circuitry may be used for both transmission and reception T Srinivasa Rao Communication Systems (EC-326) A transceiver is a small unit that combines a transmitter and a receiver. 4

Modulation T Srinivasa Rao Communication Systems (EC-326) 5

Radio communication services • • • Radio broadcasting TV broadcasting Satellite communication Mobile telephony Internet and more. . T Srinivasa Rao Communication Systems (EC-326) 6

Radio Communication • Radio Communication means any transmission, emission or reception of signs, signals, writing, images, sounds or intelligence of any nature by means of electromagnetic waves of frequencies 0 Hz - 3000 GHz propagated in space without artificial guide. T Srinivasa Rao Communication Systems (EC-326) 7

Radio Commun. - Building Blocks Basically, a radio communication system consists of a transmitter, a channel, and a receiver. ØIn a transmitter, • The input sound signal is converted into equivalent electrical current / voltage by a transducer • The transducer output is amplified by a chain of amplifiers (so that it can travel longer distance) • The purpose of the transmit antenna is to efficiently transform the electrical signal into radiation energy ØIn a receiver, • The receive antenna efficiently accepts the radiated energy and convert it to an electrical signal • As the signal suffered attenuation during travel it requires further amplification • The output transducer converts the electrical signal back into sound energy T Srinivasa Rao Communication Systems (EC-326) 8

AM & FM T Srinivasa Rao Communication Systems (EC-326) 9

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Frequency Spectrum used in Radio Communications Name Frequency Range Wave Length Application Propagation ELF 300 Hz - 3 k. Hz 100 km 1000 km Navigation, long distance communication with ships Wave tube between earth surface and the ionosphere VLF 3 k. Hz - 30 k. Hz 10 Km-100 Km Navigation, long distance communication with ships Ground propagation, stable LF 30 k. Hz - 300 k. Hz 1 Km-10 Km Navigation, long distance communication with ships Ground propagation, stable MF 300 k. Hz - 3 MHz 100 m-1 Km AM broadcasting, radio navigation Ship to Shore Comm’n. Ground-wave, sky-wave propagation. Fading HF 3 MHz - 30 MHz 10 m-100 m National and International Broadcast; Point to point telephone and telegraph Comm’n. Large perturbation, reflection in ionosphere VHF 30 MHz - 300 MHz 1 m-10 m Radio and TV broadcasting, FM Broadcast, Short distant Comm’n UHF 300 MHz - 3 GHz SHF 3 GHz - 30 GHz EHF 30 GHz - 300 GHz T Srinivasa Rao 10 cm-100 cm 1 cm-10 cm 1 mm-10 mm Diffraction Cellular telephony (GSM, NMT, AMPS), digital TV, fixed point-topoint, satellite, radar Shadowing by mountains and buildings Broadband indoor systems, Microwave links, satellite. Attenuation due to rain, snow and fog LOS communication (short distance or satellite) Attenuation due to rain, snow and fog Communication Systems (EC-326) 11

s r e t t i m s ran T o i d Ra T Srinivasa Rao Communication Systems (EC-326) 12

AM Radio Transmitter using High Carrier Power Level Master Oscillator Buffer Amplifier Harmonic Generator Class C Power Amplifiers Transmittin g Antenna Modulated Amplifier Modulating Amplifier Audio Amplifiers Modulating Signal T Srinivasa Rao Communication Systems (EC-326) 13

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Terrestrial propagation of EM Waves T Srinivasa Rao Communication Systems (EC-326) 15

AM Radio Transmitter using Low Carrier Power Level Transmittin g Antenna Class - C Master Oscillator Buffer Amplifier Harmonic Generator Modulated Amplifier Power Amplifiers Modulating Amplifier Modulating Signal T Srinivasa Rao Communication Systems (EC-326) 16

SSB Transmitter Ø The Filter Method Ø Phase Shift Method Ø Weaver’s Method. T Srinivasa Rao Communication Systems (EC-326) 17

SSB Transmitter ( Filter Method) Crystal Oscillator 100 KHz Balanced Modulator 100 KHz Modulating Amplifier Band Pass Filter RF Power Amplifiers Transmittin g Antenna (100. 3 – 103. 4 KHz) (Modulating Voltage 300 Hz-3. 4 KHz) (3. 1003 -3. 1034 MHz) First Mixer Band Pass Filter Oscillator 1 3 MHz T Srinivasa Rao (15. 1003 -15. 1034 MHz) Second Mixer Band Pass Filter RF Power Amplifiers Oscillator 2 12 MHz Communication Systems (EC-326) 18

Radio Telegraph Transmitter Ø Interrupted Continuous Wave (ICW) type or ON-OFF keying type. Ø Modulated Continuous Type (MCT) type. T Srinivasa Rao Communication Systems (EC-326) 19

Radio Telegraph Transmitter (ON-OFF Keying) Transmittin g Antenna Crystal Master Oscillator Buffer Amplifier Harmonic Generator Modulator Class C Power Amplifiers Modulating D. C. Telegraph Signal T Srinivasa Rao Communication Systems (EC-326) 20

FM Transmitters Frequency Modulation Indirect Methods Direct Methods Ø FM using Reactance tube Ø FM using Reactance FET Ø FM using Reactance BJT Ø FM using Reactance Varactor. Diode T Srinivasa Rao Communication Systems (EC-326) Ø Predistorting ØArmstrong Modulator 21

FM Transmitter using Reactance Modulator Modulating Signal (50 Hz to 15 KHZ) AF Voltage Amplifier Buffer Amplifier T Srinivasa Rao Preemphasis Circuit Three Frequency Doublers Reactance Tube Transmittin g Antenna Oiscillator Fc Frequency Tripler Communication Systems (EC-326) RF Power Amplifier 22

Capacitance Reactance Tube Modulator T Srinivasa Rao Communication Systems (EC-326) 23

Frequency Doubler. T Srinivasa Rao Communication Systems (EC-326) 24

Transmitting Antenna Carrier Amplifier Combining Filter Six Doublers 900 Phase Shift Buffer Amplifier Balanced Modulator Crystal Oscillator Pre emphasis (200 KHz) Frequency Changer Frequency Multipliers R F Power Amplifier 25 x 3 Crystal Oscillator 11. 807 MHz Armstrong FM Transmitter Predistorter Audio Amplifier T Srinivasa Rao Modulating Voltage Communication Systems (EC-326) 25

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