1 ECE 3323 Principles of Communication Systems Section 01 Introduction to Communication Systems

2 Typical Communication System

3 modulate \"mä-j€-'lÀt\ verb modulated modulating [L modulatus, pp. of modulari to play, sing, fr. modulus small measure, rhythm, dim. of modus measure — more at mete] (1615) verb transitive 1: to tune to a key or pitch 2: to adjust to or keep in proper measure or proportion : temper 3: to vary the amplitude, frequency, or phase of (a carrier wave or a light wave) for the transmission of intelligence (as by radio); also : to vary the velocity of electrons in an electron beam verb intransitive 1: to play or sing with modulation 2: to pass from one musical key into another by means of intermediary chords or notes that have some relation to both keys 3: to pass gradually from one state to another modulator \-'lÀ-t€r\ noun modulatory \-l€-'tÖr-È, -'tÕr-\ adjective © 1996 Zane Publishing, Inc. and Merriam-Webster, Incorporated

4 Reasons for Modulation The channel may not support baseband transmission (no DC for example). Baseband signal is impractical to broadcast, large antenna required Transmission of higher frequencies practical. Time/Frequency/Code Division Multiplexing.

5 Propagation of Electromagnetic Waves Ultraviolet radiation from the sun ionizes (causes free electrons) in the upper atmosphere. The ionization exists in several complicated layers. The effects of these layers are frequency dependent.

6 Ground Wave Propagation f  2 MHz, > 150 m Earth and ionosphere form a “waveguide.” EM waves will bend around the curvature of the earth for very long propagation distances.

7 Ground Wave Propagation Very Low Frequency (VLF): f  3 – 10 kHz,  100 – 30 km –Long Range Communication (Submarine) –Long Range Navigation Low Frequency (LF): f  30 – 300 kHz,  – 1000 m – Long Range Navigation –Radio Beacons Medium Frequency (MF): f  300 – 3000 kHz,  1000 – 100 m –Maritime Radio –AM Broadcasting (Daytime)

8 Sky Wave Propagation f  2 MHz –30 MHz,  150 – 10 m Limited “waveguide” effect. EM waves propagate a short distance around the curvature of the earth.

9 Sky Wave Propagation f  2 MHz –30 MHz,  150 – 10 m During the daytime sunlight generates ions that “absorb” EM waves and limit distance of propagation.

10 Sky Wave Propagation f  2 MHz –30 MHz,  150 – 10 m During the nighttime, lack of sunlight reduces ionization and absorption. EM waves are refracted by the ionosphere to reach receivers far over the horizon. Multiple paths and phasing is possible. Multiple “skips” possible.

11 Medium Frequency (MF) AM Radio (Nighttime) High Frequency (HF): 3 – 30 MHz HAM Radio Sky Wave Propagation

12 Line-of-Sight Propagation 30 MHz  f, < 10 m Ionosphere transparent to EM waves. EM waves do not bend around horizon.

13 Line-of-Sight Propagation Very High Frequency (VHF): 30 – 300 MHz –TV –FM Broadcasting –AM Aircraft Communication Ultra High Frequency (UHF): 300 – 3000 MHz –Radar –TV –Cellular Telephone

14 Satellite Communications Satellites positioned in geosynchronous orbit.

15 Line-of-Sight Propagation Super High Frequency (SHF, microwave): 3 – 30 GHz –Satellite –Microwave Links Extremely High Frequency (EHF, microwave): 30 – 300 GHz –Radar –Satellite