Technician License Course Chapter 4 Propagation, Antennas and Feed Lines

1. Technician License CourseChapter 4Propagation, Antennas and Feed Lines Lesson Plan Module 10: Practical Antennas

2. Vertically Polarized Radio Wave

3. 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)

4. Signal Polarization • Vertical – Antenna perpendicular to the earth. • Electric field also perpendicularly oriented. • Most natural and man-made radio noise is vertical • Horizontal – Antenna parallel to the earth. • Electrical field has also parallel orientation. • Used for weak signal modes at VHF, UHF, and above. • Circular – Special antenna • Can be right hand or left hand circular.

5. Practical Antennas • Rubber Duck – Flexible antenna supplied with HT’s • Horizontal Dipoles • Verticals • Loops and Yagis • Dummy Loads

6. The Dipole • Most basic antenna. • Two conductive, equal length parts. • Feed line connected in the middle. • Total length is ½ (electrical) wavelength (½ l ). • Antenna Length (in feet) = 468 / Frequency (in MHz). • Signals are strongest in the directions broadside to the antenna.

7. The Dipole

8. The Dipole • When suspended about ½ l high, it has a nominal impedance of 50 Ohms. • There are several variations: • The inverted V – Suspended from the center with the legs sloping down. • The flat top – or T antenna

9. The Ground-Plane • Simply a dipole that is oriented perpendicular to the Earth’s surface (vertical) . • One half of the dipole is replaced by the ground-plane. (1/4 l ) • Earth • Car roof or trunk lid or other metal surface. • Radial wires. • Length (in feet) = 234 / Frequency (in MHz). • Signals are omnidirectional.

10. The Ground-Plane

11. Loop Antennas – Variations • Quad - Four Sided • Delta – Three Sided • Horizontal – Parallel With the Ground • Full wavelength antennas

12. Quad Antenna The Elements are One Wavelength – ¼ Wavelength per Side

13. Directional (Beam) Antennas • Beam antennas focus or direct RF energy in a desired direction. • Gain • An apparent increase in power in the desired direction (both transmit and receive). • Yagi (rod-like elements – TV antennas). • Quad (square shape, wire loop elements).

14. Directional (Beam) Antennas Yagi Antenna Delta Loop and Quad Antennas

15. Directional (Beam) Antennas • All beam antennas have parts called elements. • Driven element is connected to the radio by the feed line. • Reflector element is on the back side. Longer than the driven element. • Director element is on the front side toward the desired direction. Shorter than the driven element.

16. Other Antennas • Rubber Duck Antenna • Not as good as a full sized antenna. • When used inside a car, much of the signal is wasted. • NVIS (Near Vertical Incidence Skywave) Antenna • Used for local communications. • Directs signal upwards • Dummy Load • Used for testing or adjusting transmitters where you do not want to send out a signal.

17. Feed Line Devices • Balun • Duplexer • Antenna switch • SWR meter • Antenna analyzer • Antenna tuner

18. Feed Line Devices • Balun – Matches balanced antenna to an unbalanced feed line. Can also match impedances. 1 to 1 4 to 1 • Duplexer –Combines / separates signals • Antenna switch - Switch between feed lines • SWR meter – Measures impedance match • Antenna analyzer - Measures antenna resonant frequency • Antenna tuner – Matches antenna system impedance to transmitter impedance.

19. Coax Feed Lines • RG-58 • RG-8 • RG-213 • RG-174 • Hardline

20. Coax Feed Lines • RG-58 - Medium Diameter Cable, OK for HF frequencies and medium power. • RG-8 – Larger Diameter Cable, OK through VHF frequencies and high power. • RG-213 - RG-8 type, with lower loss at VHF & UHF. • RG-174 - Small flexible cable, OK for short lengths. • Hardline - Low loss. Requires special procedures to keep out moisture on air core types.

21. 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).

22. Coax • Dielectric can be solid, foam, or air. • Air has lowest loss, followed by foam and solid. • Moisture in the cable will increase loss. • UV resistant jacket (black) protects cable.

23. Coax Connectors • SO-239/PL-259 • BNC • N • SMA

24. Coax Connectors • SO-239/PL-259 • Also called UHF connectors • Usable below 400MHz. • BNC • Bayonet type connector. • Good to GHz range

25. Coax Connectors • N • Commonly used at VHF and above 400Mhz. Good to GHz. • Can be water resistant • SMA • Common on newer hand held radios.

26. 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 reflected power or SWR? • 1:1 SWR is perfect. • 2:1 SWR 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.

27. 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.

28. Test and Matching Equipment • Matching device: Tuning Stub • Test equipment: Directional Wattmeter • Advanced test equipment: Antenna Analyzer

29. 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).

30. SWR Meter • Placed in the feedline between the transmitter and the antenna. • Measures the impedance mis-match between the transmitter and the antenna. (Standing Wave Ratio) • Dual needle types measure forward and reflected power simultaneously

31. 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).

32. 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.

33. 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.

34. Directional Wattmeter • Inserted in the feedline between the transmitter and antenna. • Measures forward or reflected power, depending on how the measuring element is turned. • Can be used to determine feedline match (mismatch).

35. Bird Wattmeter with slugs

36. Antenna Supports • Trees. • Towers or masts. • Covenants and antenna restrictions must be considered.

37. Soldering • Use rosin core solder for electrical connections. • Surfaces must be clean for a proper bond. • Good connections have a shiny appearance. • Poor connections have a dull or grainy appearance. (Cold solder joint). • Older equipment will have lead/tin solder, newer will have lead-free solder.

38. What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands? (T3A03) • A. Right-hand circular • B. Left-hand circular • C. Horizontal • D. Vertical

39. What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands? (T3A03) • A. Right-hand circular • B. Left-hand circular • C. Horizontal • D. Vertical

40. When using a directional antenna, how might your station be able to access a distant repeater if buildings or obstructions are blocking the direct line of sight path? (T3A05) • A. Change from vertical to horizontal polarization • B. Try to find a path that reflects signals to the repeater • C. Try the long path • D. Increase the antenna SWR

41. When using a directional antenna, how might your station be able to access a distant repeater if buildings or obstructions are blocking the direct line of sight path? (T3A05) • A. Change from vertical to horizontal polarization • B. Try to find a path that reflects signals to the repeater • C. Try the long path • D. Increase the antenna SWR

42. What is the primary purpose of a dummy load? (T7C01) • A. To prevent the radiation of signals when making tests • B. To prevent over-modulation of your transmitter • C. To improve the radiation from your antenna • D. To improve the signal to noise ratio of your receiver

43. What is the primary purpose of a dummy load? (T7C01) • A. To prevent the radiation of signals when making tests • B. To prevent over-modulation of your transmitter • C. To improve the radiation from your antenna • D. To improve the signal to noise ratio of your receiver

44. Which of the following instruments can be used to determine if an antenna is resonant at the desired operating frequency? (T7C02) • A. A VTVM • B. An antenna analyzer • C. A “Q” meter • D. A frequency counter

45. Which of the following instruments can be used to determine if an antenna is resonant at the desired operating frequency? (T7C02) • A. A VTVM • B. An antenna analyzer • C. A “Q” meter • D. A frequency counter

46. What instrument other than an SWR meter could you use to determine if a feedline and antenna are properly matched? (T7C08) • A. Voltmeter • B. Ohmmeter • C. Iambic pentameter • D. Directional wattmeter

47. What instrument other than an SWR meter could you use to determine if a feedline and antenna are properly matched? (T7C08) • A. Voltmeter • B. Ohmmeter • C. Iambic pentameter • D. Directional wattmeter

48. Which of the following is the most common cause for failure of coaxial cables? (T7C09) • A. Moisture contamination • B. Gamma rays • C. The velocity factor exceeds 1.0 • D. Overloading

49. Which of the following is the most common cause for failure of coaxial cables? (T7C09) • A. Moisture contamination • B. Gamma rays • C. The velocity factor exceeds 1.0 • D. Overloading

50. Why should the outer jacket of coaxial cable be resistant to ultraviolet light? (T7C10) • A. Ultraviolet resistant jackets prevent harmonic radiation • B. Ultraviolet light can increase losses in the cable’s jacket • C. Ultraviolet and RF signals can mix together, causing interference • D. Ultraviolet light can damage the jacket and allow water to enter the cable