Technician License Course Chapter 4

1. Technician License CourseChapter 4 Lesson Plan Module 9 – Antenna Fundamentals, Feed Lines & SWR

2. The Antenna System • Antenna: Facilitates the sending of your signal to some distant station. • Back to the falling magnet • Feed line: Connects your station to the antenna. • Test and matching equipment: Allows you to monitor antenna performance.

3. The Antenna (Some Vocabulary) • Element: The conducting part or parts of an antenna designed to radiate or receive radio waves. • Driven element: The element supplied directly with power from the transmitter • Parasitic element: A non-powered element that can add directivity to the antenna. • Feed point: Where the transmitted energy enters the antenna.

4. The Antenna (Some Vocabulary) • Polarization: The direction of the electric field relative to the surface of the earth. • Same as the physical direction • Vertical – Perpendicular to the earth • Horizontal – Parallel to the earth • Circular - Right hand or left hand

5. Vertically Polarized Electromagnetic (Radio) Wave

6. Signal Polarization • Determined by the transmitting antenna polarization. • For line-of-sight communications, differences in polarization can result in significantly weaker signals. • Vertical / Horizontal = up to 30 dB loss. • Signals that refract in the ionosphere will have their polarization randomized. (Sky-wave or Skip)

7. The Antenna (Some Vocabulary) • Omni-directional – radiates in all directions. • Directional beam – focuses radiation in specific directions. • Gain – apparent increase in power in a particular direction because energy is focused in that direction. • Expressed in decibels (dB)

8. Decibels (dB) Power Gain or Loss Decibels 3dB 6dB 10dB 20dB 30db -3dB -6dB -10dB • Twice ( X 2) • X 4 • X 10 • X 100 • X1000 • Half (½) • ¼ • 1/10

9. Antenna Radiation Patterns • Radiation patterns are a way of visualizing antenna performance. • The further the line is away from the center of the graph, the stronger the signal at that point.

11. What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization? (T3A04) • A. The modulation sidebands might become inverted • B. Signals could be significantly weaker • C. Signals have an echo effect on voices • D. Nothing significant will happen

12. What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization? (T3A04) • A. The modulation sidebands might become inverted • B. Signals could be significantly weaker • C. Signals have an echo effect on voices • D. Nothing significant will happen

13. What type of wave carries radio signals between transmitting and receiving stations? (T3A07) • A. Electromagnetic • B. Electrostatic • C. Surface acoustic • D. Magnetostrictive

14. What type of wave carries radio signals between transmitting and receiving stations? (T3A07) • A. Electromagnetic • B. Electrostatic • C. Surface acoustic • D. Magnetostrictive

15. Which of the following is a common effect of “skip” reflections between the Earth and the ionosphere? (T3A09) • A. The sidebands become reversed at each reflection • B. The polarization of the original signal is randomized • C. The apparent frequency of the received signal is shifted by a random amount • D. Signals at frequencies above 30 MHz become stronger with each reflection

16. Which of the following is a common effect of “skip” reflections between the Earth and the ionosphere? (T3A09) • A. The sidebands become reversed at each reflection • B. The polarization of the original signal is randomized • C. The apparent frequency of the received signal is shifted by a random amount • D. Signals at frequencies above 30 MHz become stronger with each reflection

17. What are the two components of a radio wave? (T3B03) • A. AC and DC • B. Voltage and current • C. Electric and magnetic fields • D. Ionizing and non-ionizing radiation

18. What are the two components of a radio wave? (T3B03) • A. AC and DC • B. Voltage and current • C. Electric and magnetic fields • D. Ionizing and non-ionizing radiation

19. What is the approximate amount of change, measured in decibels (dB), of a power increase from 5 watts to 10 watts? (T5B09) • A. 2 dB • B. 3 dB • C. 5 dB • D. 10 dB

20. What is the approximate amount of change, measured in decibels (dB), of a power increase from 5 watts to 10 watts? (T5B09) • A. 2 dB • B. 3 dB • C. 5 dB • D. 10 dB

21. What is the approximate amount of change, measured in decibels (dB), of a power increase from 20 watts to 200 watts? (T5B11) • A. 10 dB • B. 12 dB • C. 18 dB • D. 28 dB

22. What is the approximate amount of change, measured in decibels (dB), of a power increase from 20 watts to 200 watts? (T5B11) • A. 10 dB • B. 12 dB • C. 18 dB • D. 28 dB

23. What is a usual name for electromagnetic waves that travel through space? (T5C07) • A. Gravity waves • B. Sound waves • C. Radio waves • D. Pressure waves

24. What is a usual name for electromagnetic waves that travel through space? (T5C07) • A. Gravity waves • B. Sound waves • C. Radio waves • D. Pressure waves

25. Which of the following is true regarding vertical antennas? (T9A02) • A. The magnetic field is perpendicular to the Earth • B. The electric field is perpendicular to the Earth • C. The phase is inverted • D. The phase is reversed

26. Which of the following is true regarding vertical antennas? (T9A02) • A. The magnetic field is perpendicular to the Earth • B. The electric field is perpendicular to the Earth • C. The phase is inverted • D. The phase is reversed

27. What is meant by the gain of an antenna? (T9A11) • A. The additional power that is added to the transmitter power • B. The additional power that is lost in the antenna when transmitting on a higher frequency • C. The increase in signal strength in a specified direction when compared to a reference antenna • D. The increase in impedance on receive or transmit compared to a reference antenna

28. What is meant by the gain of an antenna? (T9A11) • A. The additional power that is added to the transmitter power • B. The additional power that is lost in the antenna when transmitting on a higher frequency • C. The increase in signal strength in a specified direction when compared to a reference antenna • D. The increase in impedance on receive or transmit compared to a reference antenna

29. Antenna versus Feed Line • For efficient transfer of energy from the transmitter to the feed line and from the feed line to the antenna, the various impedances need to match. • When there is mismatch of impedances, things may still work, but not as effectively as they could.

30. Feed Line types • The purpose of the feed line is to get RF energy from your station to the antenna. • Basic feed line types. • Coaxial cable (coax). • Open-wire or ladder line. • Each has a characteristic impedance, each has its unique application.

31. Feed Lines • Twin-lead lines have low loss, but require impedance matching circuits, and react with surrounding conductors. • Co-axial cables are easier to work with. The center insulation must be protected from moisture. 50 Ohm impedance is common. • Hard line co-ax has a semi-rigid or rigid shield, and has lower losses at VHF and UHF frequencies.

32. Coax • Most common feed line. • Easy to use. • Matches impedance of modern radio equipment (50 ohms). • Some loss of signal depending on coax quality (cost).

33. Open-Wire/Ladder Line • Not common today except in special applications. • Difficult to use. • Need an antenna tuner to make impedance match – but this allows a lot of flexibility. • Theoretically has very low loss.

34. Antenna Impedance • Antennas have a characteristic impedance. • Expressed in ohms – common value 50 ohms. • Depends on: • Antenna design • Height above the ground • Distance from surrounding obstacles • Frequency of operation • A million other factors

35. Impedance – AC Resistance • A quick review of a previous concept: impedance. • Antennas include characteristics of capacitors, inductors and resistors • The combined response of these component parts to alternating currents (radio waves) is called Impedance.

36. Standing Wave Ratio (SWR) • If the antenna and feed line impedances are not perfectly matched, some RF energy is not radiated into space and is returned (reflected) back to the source. • Something has to happen to this reflected energy – generally converted into heat or unwanted radio energy (bad). • Can produce high voltages or currents in the transmission line.

37. Nothing is Perfect • Although the goal is to get 100% of your radio energy radiated into space, that is virtually impossible. • What is an acceptable level of loss (reflected power or SWR?) • 1:1 is perfect. ( 1 to 1) • 2:1 should be the max you should accept (as a general rule). • Modern radios will start lowering transmitter output power automatically when SWR is above 2:1. • 3:1 is when you need to do something to reduce SWR.

38. Test and Matching Equipment • Proper impedance matching is important enough to deserve some simple test equipment as you develop your station repertoire. • Basic test equipment: SWR meter. • Matching equipment: Antenna tuner.

39. SWR Meter • The SWR meter is inserted in the feed line and indicates the mismatch that exists at that point. • You make adjustments to the antenna to minimize the reflected energy (minimum SWR).

40. Antenna Tuner • One way to make antenna matching adjustments is to use an antenna tuner. • Antenna tuners are impedance transformers (they actually do not tune the antenna). • When used appropriately they are effective. • When used inappropriately all they do is make a bad antenna look good to the transmitter…the antenna is still bad.

41. How to use an Antenna Tuner • Monitor the SWR meter. • Make adjustments on the tuner until the minimum SWR is achieved. • The impedance of the antenna is transformed to more closely match the impedance of the transmitter.

42. Which of the following is a common use of coaxial cable? (T6D11) • A. Carry dc power from a vehicle battery to a mobile radio • B. Carry RF signals between a radio and antenna • C. Secure masts, tubing, and other cylindrical objects on towers • D. Connect data signals from a TNC to a computer

43. Which of the following is a common use of coaxial cable? (T6D11) • A. Carry dc power from a vehicle battery to a mobile radio • B. Carry RF signals between a radio and antenna • C. Secure masts, tubing, and other cylindrical objects on towers • D. Connect data signals from a TNC to a computer

44. What, in general terms, is standing wave ratio (SWR)? (T7C03) • A. A measure of how well a load is matched to a transmission line • B. The ratio of high to low impedance in a feedline • C. The transmitter efficiency ratio • D. An indication of the quality of your station’s ground connection

45. What, in general terms, is standing wave ratio (SWR)? (T7C03) • A. A measure of how well a load is matched to a transmission line • B. The ratio of high to low impedance in a feedline • C. The transmitter efficiency ratio • D. An indication of the quality of your station’s ground connection

46. What reading on an SWR meter indicates a perfect impedance match between the antenna and the feedline? (T7C04) • A. 2 to 1 • B. 1 to 3 • C. 1 to 1 • D. 10 to 1

47. What reading on an SWR meter indicates a perfect impedance match between the antenna and the feedline? (T7C04) • A. 2 to 1 • B. 1 to 3 • C. 1 to 1 • D. 10 to 1

48. What is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power? (T7C05) • A. 2 to 1 • B. 1 to 2 • C. 6 to 1 • D 10 to 1

49. What is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power? (T7C05) • A. 2 to 1 • B. 1 to 2 • C. 6 to 1 • D 10 to 1

50. What does an SWR reading of 4:1 mean? (T7C06) • A. An antenna loss of 4 dB • B. A good impedance match • C. An antenna gain of 4 • D. An impedance mismatch