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Technician License Class

Technician License Class

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Technician License Class

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  1. Technician License Class Chapter 4 Propagation, Antennas, and Feed Lines

  2. Propagation • Radio waves travel outward from an antenna in a straight line • 3 phenomena possible after that: • Reflection • Bouncing wave off reflective surface • Refraction • Gradual bending of wave while traveling through atmosphere • Diffraction • Redirection of wave around edge of solid object

  3. Propagation • Line-of-sight (LOS) • Direct from transmitting antenna to receiving antenna • Radio horizon • Point at which radio signals are blocked by curvature of the earth • Slightly greater than visual horizon • Refraction increases radio horizon distance by about 15%

  4. Propagation Diffraction: Redirection of wave around edge of solid object Knife edge diffraction

  5. Propagation • Multi-path • Transmitted radio waves reflected off various objects will arrive at receive antenna at different times • Result: “Picket fencing”

  6. Propagation • Radio waves can pass through openings in solid objects • Longest dimension of opening at least ½ wavelength • Because of shorter wavelength, UHF signals can pass through buildings better than VHF signals

  7. Propagation • Tropospheric Ducting • Radio waves can travel for long distances along vertical boundaries of different temperature air layers • Propagation of 300 miles or more possible on VHF or UHF

  8. T3A01 -- What should you do if another operator reports that your station’s 2 meter signals were strong just a moment ago, but now they are weak or distorted? Change the batteries in your radio to a different type Turn on the CTCSS tone Ask the other operator to adjust his squelch control Try moving a few feet or changing the direction of your antenna if possible, as reflections may be causing multi-path distortion

  9. T3A02 -- Why are UHF signals often more effective from inside buildings than VHF signals? VHF signals lose power faster over distance The shorter wavelength allows them to more easily penetrate the structure of buildings This is incorrect; VHF works better than UHF inside buildings UHF antennas are more efficient than VHF antennas

  10. T3A06 -- What term is commonly used to describe the rapid fluttering sound sometimes heard from mobile stations that are moving while transmitting? Flip-flopping Picket fencing Frequency shifting Pulsing

  11. T3A08 -- Which of the following is a likely cause of irregular fading of signals received by ionospheric reflection? Frequency shift due to Faraday rotation Interference from thunderstorms Random combining of signals arriving via different paths Intermodulation distortion

  12. T3C05 -- Which of the following effects might cause radio signals to be heard despite obstructions between the transmitting and receiving stations? Knife-edge diffraction Faraday rotation Quantum tunneling Doppler shift

  13. T3C06 -- What mode is responsible for allowing over-the-horizon VHF and UHF communications to ranges of approximately 300 miles on a regular basis? Tropospheric scatter D layer refraction F2 layer refraction Faraday rotation

  14. T3C08 -- What causes tropospheric ducting? Discharges of lightning during electrical storms Sunspots and solar flares Updrafts from hurricanes and tornadoes Temperature inversions in the atmosphere

  15. T3C10 -- What is the radio horizon? The distance over which two stations can communicate by direct path The distance from the ground to a horizontally mounted antenna The farthest point you can see when standing at the base of your antenna tower The shortest distance between two points on the Earth's surface

  16. T3C11 -- Why do VHF and UHF radio signals usually travel somewhat farther than the visual line of sight distance between two stations? Radio signals move somewhat faster than the speed of light Radio waves are not blocked by dust particles The Earth seems less curved to radio waves than to light Radio waves are blocked by dust particles

  17. Propagation • Ionosphere • The upper layers of the atmosphere are ionized by UV radiation from the sun • 30 to 260 miles above the Earth’s surface

  18. Propagation • Ionosphere • The ionosphere is divided into layers or regions • Each layer has unique characteristics

  19. Propagation • Ionosphere • Transmissions in some radio frequency bands (e.g., HF & lower VHF) will be reflected off the ionosphere and return to earth • Called “skip” • Skip distances are well beyond the range of line-of-sight • Several hundred to several thousand miles • Maximum of about 2500 miles for a single hop • Can have multiple hops

  20. Propagation • Ionosphere • The higher the amount of ionization, the better radio waves are refracted by the ionosphere • Amount of ionization varies with time of day • Sunrise to sunset  higher ionization level • Amount of ionization varies with sunspot activity • More sunspots  higher ionization level • Larger sunspots  higher ionization level • Number and size of sunspots varies over an 11-year cycle • Currently in declining portion of Cycle 24

  21. Propagation • Ionosphere

  22. Propagation • Ionosphere • Skip is refraction (bending), not reflection (bouncing) • The shorter the wavelength (higher frequency), the less the signal is refracted (bent). • At some given frequency, the wave is no longer bent enough to return to earth • Known as the “critical frequency” • Skip normally occurs in the F-layer (F1 & F2) • Can occur in the E-layer

  23. Propagation • Ionosphere • The highest frequency that can be used to communicate between 2 points is called the Maximum Useable Frequency (MUF) • The lowest frequency that can be used to communicate between 2 points is called the Lowest Useable Frequency (LUF) • MUF & LUF vary over any 24-hour period depending on the amount of ionization in the ionosphere

  24. Propagation • Ionosphere

  25. Propagation • Ionosphere • E-Layer Propagation • Sporadic-E • Can occur any time during the solar cycle • Highest probability: Early summer and mid-winter • HF Bands: 10 meters, 6 meters, and 2 meters • Aurora (Northern latitudes) • Rapid signal strength changes • Sounds fluttery or distorted • Primarily on 6 meters • Meteor scatter • Primarily 6 meters

  26. Propagation • Ionosphere • The lowers regions of the ionosphere absorb radio waves • Primarily D-layer • Some absorption in E-layer • The longer the wavelength (lower frequency), the more absorption • Little to no communications possible on lower frequency bands during the day when D and E layer are present

  27. T3A11 -- Which part of the atmosphere enables the propagation of radio signals around the world? The stratosphere The troposphere The ionosphere The magnetosphere

  28. T3C01 -- Why are direct (not via a repeater) UHF signals rarely heard from stations outside your local coverage area? They are too weak to go very far FCC regulations prohibit them from going more than 50 miles UHF signals are usually not reflected by the ionosphere They collide with trees and shrubbery and fade out

  29. T3C02 -- Which of the following might be happening when VHF signals are being received from long distances? Signals are being reflected from outer space Signals are arriving by sub-surface ducting Signals are being reflected by lightning storms in your area Signals are being refracted from a sporadic E layer

  30. T3C03 (B)-- What is a characteristic of VHF signals received via auroral reflection? Signals from distances of 10,000 or more miles are common The signals exhibit rapid fluctuations of strength and often sound distorted These types of signals occur only during winter nighttime hours These types of signals are generally strongest when your antenna is aimed west

  31. T3C04 -- Which of the following propagation types is most commonly associated with occasional strong over-the-horizon signals on the 10, 6, and 2 meter bands? Backscatter Sporadic E D layer absorption Gray-line propagation

  32. T3C07 -- What band is best suited for communicating via meteor scatter? 10 meters 6 meters 2 meters 70 cm

  33. T3C09 -- What is generally the best time for long-distance 10 meter band propagation via the F layer? From dawn to shortly after sunset during periods of high sunspot activity From shortly after sunset to dawn during periods of high sunspot activity From dawn to shortly after sunset during periods of low sunspot activity From shortly after sunset to dawn during periods of low sunspot activity

  34. T3C12 -- Which of the following bands may provide long distance communications during the peak of the sunspot cycle? Six or ten meters 23 centimeters 70 centimeters or 1.25 meters All of these choices are correct

  35. Antenna Fundamentals • Definitions: • Antenna: Converts an RF electrical signal into an electromagnetic wave (radio wave) or vice versa • Any electrical conductor can act as an antenna • Some sizes and configurations work better than others • Feed-line: Conducts the RF electrical signal to/from the antenna • a.k.a. Transmission line

  36. Antenna Fundamentals • Definitions: • Feed Point: Place where the feed-line is connected to the antenna • Feed Point Impedance: Ratio of RF voltage to RF current at the feed point • If impedance is purely resistive (no reactance) then antenna is said to be “resonant”

  37. Antenna Fundamentals • Definitions: • Antenna Elements: Conductive parts of an antenna • Driven Element: Element that feed-line is connected to • Driven Array: More than one driven element • Parasitic Element(s): Element(s) not directly connected to feed-line • Reflector • Director

  38. Antenna Fundamentals • Polarization • An electromagnetic wave consists of an electric wave and magnetic wave that propagate at right angles to each other • Polarization is the orientation of the electric wave with respect to the earth

  39. Antenna Fundamentals • Polarization • If the electric wave is horizontal (parallel to the ground), then wave is said to be horizontally polarized • If electric wave is vertical (perpendicular to the ground), then wave is said to be vertically polarized

  40. Antenna Fundamentals • Polarization

  41. Antenna Fundamentals • Polarization • The direction of the electric field is the same as the orientation of the antenna element • Loop antennas and circular polarization are exceptions • At VHF and UHF frequencies, if polarizations of transmit and receive antenna do not match, reduced received signal strength results • Polarization of refracted sky wave signals is random and continuously changing • Elliptically polarized • An antenna of any orientation may be used

  42. T3A04 -- 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? The modulation sidebands might become inverted Signals could be significantly weaker Signals have an echo effect on voices Nothing significant will happen

  43. T3A07 -- What type of wave carries radio signals between transmitting and receiving stations? Electromagnetic Electrostatic Surface acoustic Magnetostrictive

  44. T3A09 -- Which of the following results from the fact that skip signals refracted from the ionosphere are elliptically polarized? Digital modes are unusable Either vertically or horizontally polarized antennas may be used for transmission or reception FM voice is unusable Both the transmitting and receiving antennas must be of the same polarization

  45. T3B02 -- What property of a radio wave is used to describe its polarization? The orientation of the electric field The orientation of the magnetic field The ratio of the energy in the magnetic field to the energy in the electric field The ratio of the velocity to the wavelength

  46. T3B03 -- What are the two components of a radio wave? AC and DC Voltage and current Electric and magnetic fields Ionizing and non-ionizing radiation

  47. T5C07 -- What is a usual name for electromagnetic waves that travel through space? Gravity waves Sound waves Radio waves Pressure waves

  48. T9A02 -- Which of the following is true regarding vertical antennas? The magnetic field is perpendicular to the Earth The electric field is perpendicular to the Earth The phase is inverted The phase is reversed

  49. Antenna Fundamentals • Decibels • The difference in strength between 2 signals is often expressed in decibels (dB) • Ratio between 2 values… a comparison • Based on logarithmic scale

  50. Antenna Fundamentals • Decibels • Commonly used to: • Specify gain of an amplifier • Specify gain of an antenna • Specify loss in a feed line Comparing output vs input level