2. Radio & Telecommunications Systems 1 Radio & Telecommunications Systems (1.0) Lecturer: P.M. Cheung (room 326) email:pmcheung@vtc.edu.hk Contact Hours: Lecture: 30 hours (room 310) Tutorial: 15 hours (room324) Lab. :4 experiments(room 324)

3. Radio & Telecommunications Systems 2 Content:1. EM wave & Antenna 2. Transmitters & Receivers 3. Telephone systems 4. TV Systems Assessment:Course work – 50% (assignment:10%, lab:20%, test: 20%) Exam.- 50% Textbook: Electronic Communications Systems, 3 rd ed.,Dungan, Delmar No lecture notes will be delivered. Download from intranet: http://172.26.126.61/student

4. Radio & Telecommunications Systems 3 Aims establish an understanding of the elementary principles employed in radio transmitter and receiver systems introduce the basic system knowledge of various kinds of local telecommunications systems Co-requisites Telecommunications Principles 1

5. Radio & Telecommunications Systems 4 Learning Strategies emphasis on the general aspects and appreciation of radio and telecommunications systems practical examples of various telecommunications systems will be used to promote learning Assessment Continuous assessment - 50% Examination - 50%

6. Radio & Telecommunications Systems 5 Content Area Electromagnetic wave and antenna systems radiation of electromagnetic wave modes of propagation parameters of aerial practical aerials Radio transmitters and receivers block diagrams of : AM transmitters, FM transmitters, superheterodyne receiver diode detector

7. Radio & Telecommunications Systems 6 Telephone systems fixed network technology, space and time switching local loop, signalling in call establishment overview of mobile communications; cellular communications, multiple access Television systems scanning, composite video, PAL/NTSC systems, TV transmission/reception overview of satellite boardcast; orbit, earth station, satellite TV

8. Radio & Telecommunications Systems 7 Radio Wave Propagation Radio wave characteristics Radiation from an antenna Propagation characteristics

9. Radio & Telecommunications Systems 8 Radio Wave Characteristics the radiation concept of radio waves dropping a pebble into a pool of water water to move up and down disturbance transmitted as expanding circles of waves transverse wave or traveling wave occurring perpendicular to the direction of propagation. e.g. electromagnetic waves radiated by antennas

10. Radio & Telecommunications Systems 9 Frequency the number of cycles of a sine wave completed in one second expressed in Hz (Figure 1) Radio Frequencies (RF) frequencies between 3 kHz and 300 GHz commonly used in radio communication. Wavelength (  the space occupied by one full cycle of a radio wave at any given instant (Figure 2) = c / f c = velocity of radio wave = 3x10 8 m/s

11. Radio & Telecommunications Systems 10 Figure 1 - Sine wave characteristic

12. Radio & Telecommunications Systems 11 Figure 2 - Concept of a wavelength

13. Radio & Telecommunications Systems 12 Electromagnetic Radiation complex form of energy containing both electric and magnetic fields moving electric field always creates a magnetic field moving magnetic field always creates an electric field lines of force of these fields are perpendicular to each other (Figure 3)

14. Radio & Telecommunications Systems 13 Figure 3 - Electromagnetic lines of force

15. Radio & Telecommunications Systems 14 Wave Polarization determined by the direction of the electric field of the wave with respect to earth vertically polarized electric field of the wave is vertical to the earth (Figure 4A) horizontally polarized electric field is horizontal to the earth (Figure 4B) position of the transmitting antenna determines whether the wave will be vertically or horizontally polarized

16. Radio & Telecommunications Systems 15 Figure 4A - Vertically polarized wave

17. Radio & Telecommunications Systems 16 Figure 4B - Horizontally polarized wave

18. Radio & Telecommunications Systems 17 Radio & Telecommunications Systems Induction/Radiation Field Free Space Impedance Modes of Propagation

19. Radio & Telecommunications Systems 18 Radiated field energy radiated from the conductor or aerial in the form of an electromagnetic wave electric and magnetic fields are at right angles to each other mutually at right angles to the direction of propagation (Figure 1) magnitude proportional to the frequency of the wave and inversely proportional to the distance from the aerial

20. Radio & Telecommunications Systems 19 Figure 1 - Electromagnetic wave

21. Radio & Telecommunications Systems 20 Figure 5 - Radiation from an aerial

22. Radio & Telecommunications Systems 21 Induction field near the aerial energy that is not radiated away from the aerial magnitude diminishes inversely as the square of the distance from the aerial the induction field larger than the radiation field at distances greater than /2  radiation field is the larger

23. Radio & Telecommunications Systems 22 Free Space Impedance amplitudes of electric field E & magnetic field H constant relationship to each other. Impedance of free space =E (volts/meter) / H (ampere-turns/meter) =120   =377 

24. Radio & Telecommunications Systems 23 Propagation Characteristics electromagnetic wave sent out from an antenna ground wave part of the radiated energy travels along or near the surface of the earth sky wave another part travels from the antenna upward into space space wave energy that travels directly from the transmitting antenna to the receiving antenna

25. Radio & Telecommunications Systems 24 Ground Waves primary mode of propagation in LF band (30 - 300 KHz) MF band (300 KHz - 3MHz) follow the curvature of the earth and actually travel beyond the horizon (Figure 2) as the frequency increases more effectively absorbed by the irregularities on the earth's surface hills, mountains, trees, and buildings

26. Radio & Telecommunications Systems 25 Figure 2 - Ground wave propagation

27. Radio & Telecommunications Systems 26 Space Waves transmitted signal above 4 or 5 MHz usable ground wave signal is limited to a few miles. signals can be transmitted farther using the space or direct wave (Figure 3) used primarily in VHF band (30 - 300 MHz) UHF band (300 MHz - 3 GHz) limited to line-of-sight distances energy in radio waves at frequencies above 30 MHz moves through space in straight lines like light waves

28. Radio & Telecommunications Systems 27 Figure 3 - Space wave propagation

29. Radio & Telecommunications Systems 28 Radio Horizon about one third greater than that of the optical horizon caused by refraction in the earth's lower atmosphere density of the earth's atmosphere decreases linearly as height increases effectively bending the wave slightly downward follows the curvature of the earth beyond the optical horizon

30. Radio & Telecommunications Systems 29 radio horizon for both transmitting and receiving antennas : D t = 4  t or D r = 4  r whereD t and Dr = radio horizon distance in kilometers H t and H r = height of transmitting (receiving) antenna in meters maximum space wave communications distance is the sum of the numbers obtained by for both antennas. D max = 4  t + 4  r or D max =D t + D r

31. Radio & Telecommunications Systems 30 Sky Waves ionized layers of the atmosphere between 50 - 400km above the surface of the earth at certain frequencies and radiation angles the ionosphere reflects radio waves radio waves at other frequencies and angles are refracted and return to earth (Figure 4) amount of refraction depends on frequency of the wave density of the ionized layer angle at which the wave enters the ionosphere.

32. Radio & Telecommunications Systems 31 Figure 4 - Sky wave propagation

33. Radio & Telecommunications Systems 32 long distance communications carrier frequencies in the MF and HF bands (3 - 30 MHz) waves radiated at these frequencies can be refracted back to earth waves at frequencies above 30 MHz penetrate the ionosphere and continue moving out into space

34. Radio & Telecommunications Systems 33 The Ionosphere: atmospheric conditions continuously change hourly, daily, monthly, seasonally, yearly….. undesirable results are signal absorption, dispersion and fading atmospheric conditions have their greatest effect on the ionosphere graphic illustration of the designations of the ionospheric layers and their approximate altitudes is shown in Figure 1.

35. Radio & Telecommunications Systems 34 Figure 1 - Layers in the ionosphere

36. Radio & Telecommunications Systems 35 D layer, 50-90 km above the earth lowest layer exists only in the daytime ionization is relatively weak does not affect the travel direction of radio waves absorb energy from the electromagnetic wave attenuates the sky wave

37. Radio & Telecommunications Systems 36 MF band signals are completely absorbed by the D layer at night D layer disappears long distance MF transmissions via sky wave E layer, 90-150 km above earth maximum density at noon ionization is so weak at night the layer may disappear

38. Radio & Telecommunications Systems 37 F layer, 200-400 km above earth splits into F 1 and F 2 in the daytime F 2 varying from summer to winter F 1 layer, 200-220 km above the surface of the earth. F 2 layer, 250-350km in winter, 300-500km in summer

39. Radio & Telecommunications Systems 38 Frequency bands and major services

40. Radio & Telecommunications Systems 39 Refraction of an Electromagnetic Wave electromagnetic wave travelling in one medium passes into a different medium direction of travel will probably be altered wave is said to be refracted. The ratio is a constant for a given pair of media and is known as the refractive index for the media.

41. Radio & Telecommunications Systems 40 wave is transmitted through a number of thin strips (Figure 2) each strip having an absolute refractive index lower than that of the strip immediately below it wave will pass from higher to lower absolute refractive progressively bent away from the normal wave will be continuously refracted

42. Radio & Telecommunications Systems 41 Figure 2 - Refraction of an electromagnetic wave

43. Radio & Telecommunications Systems 42 refractive index n of a layer is related to both the frequency f of the wave and the electron density N according to:

44. Radio & Telecommunications Systems 43 Figure 3 - Effect on ionospheric refraction

45. Radio & Telecommunications Systems 44 Critical Frequency the max frequency that can be radiated vertically upwards by a radio transmitter and be returned to earth wave that travels to the top of the layer electron density is at its maximum value angle of refraction becomes 90 o angle of incidence is 0 o therefore

46. Radio & Telecommunications Systems 45 Maximum Usable Frequency (MUF) highest frequency that can be used to establish communication using the sky wave between two points determined by both the angle of incidence of the radio wave and the critical frequency of the layer; thus

47. Radio & Telecommunications Systems 46 Optimum Working Frequency (OWF) ionospheric fluctuations often take place operation of a link at the m.u.f. would not be reliable frequency of about 85% of the m.u.f. used to operate a sky-wave link known as the optimum working frequency or o.w.f since the m.u.f. will vary over the working day necessary to change the transmitter frequency as propagation condition varies

48. Radio & Telecommunications Systems 47 Reference Dungan F.R., “Electronic Communications Systems,” 3rd ed., ITP Green D.C., “Radio Systems for Technicians,” Longman