- radiation and wave propagation - - Which of the following low noise transistors is commonly used at microwave frequencies? a. MOSFET b. GASFET c. MESFET d. JFET ans: c- Which of the following is most affected by knife-edge refraction? a. Very high and ultra high frequencies b. High frequency c. Medium frequency d. Low frequency ans: a- Which ionosphere layer has an average height of 225 km at night? a. D layer b. E layer c. F1 layer d. F2 layer ans: d- __________ is the amount of voltage induced in a wave by an electromagnetic wave. a. Receive voltage b. Magnetic induction c. Field strength d. Power density ans: c- An electromagnetic wave consists of _________. a. both electric and magnetic fields b. an electric field only c. a magnetic field only d. non-magnetic field only ans: a- What is the lowest layer of the ionosphere? a. F1 b. F2 c. E d. D ans: d- Who profounded electromagnetic radiation theory? a. Sir Edward Appleton b. James Clerk Maxwell c. Christian Huygens d. Sir Isaac Newton ans: b- The D, E and F layers are known as ________. a. Mark-Space layers b. Davinson-Miller layers c. Kennely-Heaviside layers d. Appleton layers ans: c- Different grouping of the electromagnetic spectrum. a. Band b. Bandwidth c. Channel d. Group ans: a- What is the relation in degrees of the electric and magnetic fields in an electromagnetic wave? a. 180 degrees b. 90 degrees c. 270 degrees d. 45 degrees ans: b- A changing electric field gives rise to ________. a. a magnetic field b. sound field c. electromagnetic waves d. near and far fields ans: a- Frequencies in UHF range propagate by means of a. ground waves b. sky waves c. surface waves d. space waves ans: d- In electromagnetic waves, polarization _________. a. is caused by reflection b. is due to the transverse nature of the waves c. results from the longitudinal nature of the waves d. is always vertical in an isotropic medium ans: b- Electromagnetic waves are refracted when they _________. a. pass into a medium of different dielectric constants b. are polarized at right angles to the direction of propagation c. encounter a perfectly conducting surface d. pass through a small slot in a conducting plane ans: a- What is the highest layer of the atmosphere? a. Ionosphere b. Stratosphere c. Troposphere d. Ozone layer ans: a- What is the thickest layer of the ionosphere? a. F sub 2 b. F sub 1 c. D d. E ans: a- Effective earth radius to true earth radius ratio. a. Index of refraction b. K factor c. Fresnel zone d. Path profile ans: b- Fading due to interference between direct and reflected rays. a. Atmospheric-multipath b. Fresnel zone c. Reflection-multipath d. Rayleigh fading ans: c- The layer that reflects very low frequency waves and absorbs medium frequency waves. a. D layer b. E layer c. F1 layer d. F2 layer ans: a- What layer is used for high-frequency daytime propagation? a. D layer b. E layer c. F1 layer d. F2 layer ans: b- What is the highest frequency that can be sent straight upward and be returned to earth? a. MUF b. Skip frequency c. Critical frequency d. Gyro frequency ans: c- High frequency range is from a. 0.3 to 3 MHz b. 3 to 30 MHz c. 30 to 300 MHz d. 3 to 30 MHz ans: b- Medium frequency range is from a. 0.01 to 0.03 MHz b. 0.03 to 0.3 MHz c. 0.3 to 3 MHz d. 3 to 30 MHz ans: c- In tropospheric scatter propagation, the attenuation is dependent on a. scatter angle b. take-off angle c. antenna size d. the troposphere ans: a- If the transmitter power remains constant, an increase in the frequency of the sky wave will a. lengthen the skip distance b. increase the range of the ground wave c. reduce the length of the skip distance d. have no effect on the ground wave range ans: a- What is the unit of electric field strength? a. Volts per square meter b. Volt per square cm c. Volts per meter d. Millivolt per watt ans: c- Velocity of a radio wave in free space. a. 186,000 miles per sec b. 300 x 10^ 6 meters per sec c. 162,000 nautical mile per sec d. all of the above ans: d- Refers to the direction of the electric field vector in space. a. Polarization b. Directivity c. Radiation d. ERP ans: a- An TEM wave whose polarization rotates. a. Vertically polarized b. Omnidirectional c. Horizontally polarized d. Circularly polarized ans: d- Velocity of light in free space. a. 300 x 10 raised to 6 m/s b. 300 x 10 raised to 6 km/s c. 186,000 km/s d. 186,000 m/s ans: a- What is the effective radiated power of a repeater with 200 W transmitter power output, 4 dB feedline loss, 4 dB duplexer and circular loss, and 10 dB feedline antenna gain? a. 2000 W b. 126 W c. 317 W d. 260 W ans: c- Radiowave that is far from its sources is called a. plane wave b. isotropic wave c. vertical wave d. horizontal wave ans: a- Light goes from medium A to medium B at angle of incidence of 40 degrees. The angle of refraction is 30 degrees. The speed of light in B a. is the same as that in A b. is greater than that in A c. may be any of these, depending on the specific medium d. is less than that in A ans: d- In a vacuum the speed of an electromagnetic wave a. depends on its constant b. depends on its wavelength c. depends on its electric and magnetic fields d. is a universal constant ans: d- The depth of an object submerged in a transparent liquid a. always seems more than its actual depth b. may seem less or more than its actual depth, depending on the object c. always seems less than its actual depth d. may seem less or more than its actual depth, depending on the transparent liquid ans: c- What is a wavefront? a. A voltage pulse in a conductor b. A current in a conductor c. A fixed point in an electromagnetic wave d. A voltage pulse across a resistor ans: c- VHF ship station transmitters must have the capability of reducing carrier power to a. 1 W b. 10 W c. 25 W d. 50 W ans: a- Most of the effects an electromagnetic wave produces when it interacts with matter are due to its a. magnetic field b. speed c. frequency d. electric field ans: d- A mobile receiver experiences "dead" areas of reception as a result of a. atmospheric absorption b. tropospheric scatter c. sporadic E d. shading of the RF signal by hills and trees ans: d- When the electric field is perpendicular to the surface of the earth, what is the polarization of the TEM wave? a. Elliptical b. Vertical c. Horizontal d. Circular ans: b- When the magnetic field is perpendicular to the surface of the earth, what is the polarization of the TEM wave? a. Circular b. Horizontal c. Vertical d. Elliptical ans: b- When the magnetic field is parallel to the surface of the earth, what is the polarization of the TEM wave? a. Elliptical b. Horizontal c. Vertical d. Circular ans: c- What are the two interrelated fields considered to make up an electromagnetic wave? a. An electric field and a current field b. An electric field and a voltage field c. An electric field and a magnetic field d. A voltage and current fields ans: c- How does the bandwidth of a transmitted signal affect selective fading? a. It is more pronounced at narrow bandwidths b. It is equally pronounced at both narrow and wide bandwidths c. It is more pronounced at wide bandwidths d. The receiver bandwidth determines the selective fading ans: c- A wide-bandwidth communications systems in which the RF carrier varies according to some predetermined sequence. a. Amplitude compandored single sideband b. SITOR c. Spread spectrum communication d. Time-domain frequency modulation ans: c- A changing magnetic field gives rise to a. sound field b. magnetic field c. electric field d. nothing in particular ans: c- When a space-wave signal passes over a mountain ridge, a small part of the signal is diffracted down the far side of the mountain. The phenomenon is called a. discontinuity scattering b. tropospheric ducting c. knife-edge diffraction d. space-wave refraction ans: c- The index of refraction of a material medium a. is greater than 1 b. is less than 1 c. is equal to 1 d. may be any of the above ans: a- At what speed do electromagnetic waves travel in free space? a. Approximately 468 million meters per second b. Approximately 186300 feet per second c. Approximately 300 million meters per second d. Approximately 300 million miles per second ans: c- What is the effective earth radius when surface refractivity, Ns equals 300? a. 6370 km b. 7270 km c. 7950 km d. 8500 km ans: d- If Ns = 250, what is the earth radius k-factor? a. 1.23 b. 1.29 c. 1.33 d. 1.32 ans: a- Electric field that lies in a plane perpendicular to the earth's surface. a. Vertical polarization b. Horizontal polarization c. Circular polarization d. Elliptical polarization ans: a- Electric field that lies in a plane parallel to the earth's surface. a. Vertical polarization b. Horizontal polarization c. Circular polarization d. Elliptical polarization ans: b- Indicate which one of the following terms applies to troposcatter propagation. a. SIDs b. Fading c. Atmospheric storms d. Faraday rotation ans: b- VLF waves are used for some types of services because a. of the low power required b. the transmitting antennas are of convenient size c. they are very reliable d. they penetrate the ionosphere easily ans: c- Indicate which of the following frequencies cannot be used for reliable beyond-the-horizon terrestrial communications without repeaters. a. 20 kHz b. 15 MHz c. 900 MHz d. 12 GHz ans: d- High-frequency waves are a. absorbed by the F2 layer b. reflected by the D layer c. capable of use for long-distance communications on the moon d. affected by the solar cycle ans: d- Distances near the skip distance should be used for sky-wave propagation a. to avoid tilting b. to prevent sky-wave and upper ray interference c. to avoid the Faraday effect d. so as not to exceed the critical frequency ans: b- A ship-to-ship communications system is plagued by fading. The best solution seems to be the use of a. a more directional antenna b. a broadband antenna c. frequency diversity d. space diversity ans: c- A range of microwave frequencies more easily passed by the atmosphere than are the others is called a a. window b. critical frequency c. gyro frequency range d. resonance in the atmosphere ans: a- Frequencies in the UHF range normally propagate by means of a. ground waves b. sky waves c. surface waves d. space waves ans: d- Tropospheric scatter is used with frequencies in the following range a. HF b. VHF c. UHF d. VLF ans: c- The ground wave eventually disappears as one moves away from the transmitter, because of a. interference from the sky wave b. loss of line-of-sight conditions c. maximum single-hop distance limitation d. tilting ans: d- In electromagnetic waves, polarization means a. the physical orientation of magnetic field in space b. the physical orientation of electric field in space c. ionization d. the presence of positive and negative ions ans: b- As electromagnetic waves travel in free space, only one of the following can happen to them. a. absorption b. attenuation c. refraction d. reflection ans: b- The absorption of a radio waves by the atmosphere depends on a. their frequency b. their distance from the transmitter c. the polarization of the waves d. the polarization of the atmosphere ans: a- Diffraction of electromagnetic waves a. is caused by reflections from the ground b. arises only with spherical wavefronts c. will occur when the waves pass through a large slot d. may occur around the edge of a sharp obstacle ans: d- In an electromagnetic wave the electric field is a. parallel to both magnetic field and the wave direction b. perpendicular to both the magnetic field and the wave direction c. parallel to the magnetic field and perpendicular to the wave direction d. perpendicular to the magnetic field and parallel to the wave direction ans: b- The highest frequencies are found in a. X-rays b. radio waves c. ultraviolet rays d. radar waves ans: a- Electromagnetic waves transport a. wavelength b. charge c. frequency d. energy ans: d- The ionosphere is a region of ionized gas in the upper atmosphere. The ionosphere is responsible for a. the blue color of the sky b. rainbows c. long-distance radio communications d. the ability of satellites to orbit the earth ans: c- Light of which the following colors has the shortest wavelength? a. red b. yellow c. blue d. green ans: c- The quality in sound that corresponds to color in light is a. amplitude b. resonance c. waveform d. pitch ans: d- All real images a. are erect b. can appear on a screen c. are invalid d. cannot appear on a screen ans: b- When a beam of light enters one medium from another, a quality that never changes is its a. direction b. frequency c. speed d. wavelength ans: b- Relative to the angle of incidence, the angle of refraction a. is smaller b. is larger c. is the same d. either A or B above ans: d- A light ray enters one medium from another along the normal. The angle of refraction is a. 0 b. 90 degrees c. equal the critical angle d. dependent on the indexes of refraction of the two media ans: d- What layer aids MF surface-wave propagation a little and reflects some HF waves in daytime? a. E layer b. D layer c. F1 layer d. F2 layer ans: a- Dispersion is the term used to describe a. the splitting of white light into its component colors in refraction b. the propagation of light in straight lines c. the bending of a beam of light when it goes from one medium to another d. the bending of a beam of light when it strikes a mirror ans: a- The depth of an objects submerged in a transparent liquid a. always seems less than its actual depth b. always seems more than its actual depth c. may seem more than its actual depth, depending on the index of refraction of the liquid d. may seem less or more than its actual depth, depending on the angle of view ans: a- Total internal reflection can occur when light passes from one medium to another a. that has a lower index of refraction b. that has a higher index of refraction c. that has the same index of refraction d. at less than the critical angle ans: a- When a light ray approaches a glass-air interface from the glass side at the critical angle, the angle of refraction is a. 0 b. 90 degrees c. 45 degrees d. equal the angle of incidence ans: b- The brightness of light source is called its luminous intensity, whose unit is a. candela b. lux c. lumen d. footcandle ans: a- Luminous efficiency is least for a a. low-wattage light bulb b. mercury vapor lamp c. high-wattage light bulb d. fluorescent tube ans: a- The minimum illumination recommendation for reading is a. 8000 cd b. 8000 lx c. 8000 lm d. 800 W ans: b- Light enters a glass plate whose index of refraction is 1.6 at an angle of incidence of 30 degrees. The angle of refraction is a. 18 degrees b. 48 degrees c. 19 degrees d. 53 degrees ans: a- Light leaves a slab of transparent material whose index of refraction is 2.0 at an angle of refraction of 0 degree. The angle of incidence is a. 0 degrees b. 45 degrees c. 30 degrees d. 90 degrees ans: a- Light enters a glass plate at an angle of incidence of 40 degrees and is refracted at an angle refraction of 25 degrees. The index refraction of the glass is a. 0.625 b. 1.52 c. 0.66 d. 1.6 ans: b- An underwater swimmer shines a flashlight beam upward at an angle of incidence of 40 degrees. The angle of refraction is 60 degrees. The index of refraction of water is a. 0.67 b. 1.3 c. 0.74 d. 1.5 ans: b- The critical angle of incidence for light going from crown glass (n = 1.5) to ice (n = 1.3) is a. 12 degrees b. 50 degrees c. 42 degrees d. 60 degrees ans: d- The solid angle subtended by a hemisphere about its center is a. pi/2 sr b. 2pi sr c. pi sr d. depends on the radius of the hemisphere ans: b- The luminous flux emitted by a 60-cd isotropic light source is concentrated on an area of 0.5 m^2. The illumination of the area is a. 9.6 lx b. 377 lx c. 120 lx d. 1508 lx ans: d- Microwave signals propagate by way of the a. direct wave b. sky wave c. surface wave d. standing wave ans: a- The ionosphere causes radio signals to be a. diffused b. absorbed c. refracted d. reflected ans: c- Groundwave communications is most effective in what frequency range? a. 300 kHz to 3 MHz b. 3 to 30 MHz c. 30 to 300 MHz d. above 300 MHz ans: a- The ionosphere has its greatest effect on signals in what frequency range? a. 300 kHz to 3 MHz b. 3 to 30 MHz c. 30 to 300 MHz d. above 300 MHz ans: b- The type of radio wave responsible for long-distance communication by multiple skips is the a. ground wave b. direct wave c. surface wave d. sky wave ans: d- Line-of-sight communications is not a factor in which frequency range? a. VHF b. UHF c. HF d. Microwave ans: c- A microwave-transmitting antenna is 550 ft. high. The receiving antenna is 200 ft. high. The minimum transmission distance is a. 20 mi b. 33.2 mi c. 38.7 mi d. 53.2 mi ans: d- To increase the transmission distance of UHF signal, which of the following should be done? a. increase antenna gain b. increase antenna height c. increase transmitter power d. increase receiver sensitivity ans: b- States that power density is inversely proportional to the distance from its source. a. Principle of Reciprocity b. Inverse Square Law c. Huygen's Principle d. Faraday's Law ans: b- _________ gets in contact with the ionosphere and reflected by it. a. Space wave b. Sky wave c. Surface wave d. Satellite wave ans: b- Highest layer in the ionosphere. a. F1 b. D c. F2 d. E ans: c- Next lowest layer in the ionosphere. a. D b. E c. F1 d. F2 ans: b- What is the primary cause of ionization in the atmosphere? a. Sun spot b. Cosmic rays c. Galactic disturbance d. Ultraviolet radiation ans: d- Which layer does not disappear at night? a. D b. E c. F1 d. F2 ans: d- Which of the following uses surface wave propagation? a. ELF b. VLF c. MF d. All of these ans: d- The ability of the ionosphere to reflect a radio wave back to the earth is determined by a. operating frequency b. ion density c. angle of incidence d. all of these ans: d- Highest frequency that can be used for skywave propagation between two given points on earth. a. Critical frequency b. MUF c. Cut-off frequency d. UHF ans: b- The shortest distance measured along the earth's surface that a skywave is returned to earth. a. MUF b. Quarter-wavelength c. Skip distance d. Skip zone ans: c- Fluctuations in the signal strength at the receiver. a. Interference b. Fading c. Tracking d. Variable frequency ans: b- Two or more antennas are used separated by several wavelengths. a. Space diversity b. Frequency diversity c. Hybrid diversity d. Polarization diversity ans: a- Two or more receivers are used using a single antenna. a. Space diversity b. Frequency diversity c. Hybrid diversity d. Polarization diversity ans: b- One of the following is not a cause of fading. a. Interference between upper and lower rays of a sky wave. b. Skywaves arriving at different number of hops c. Interference due to ground reflected wave and skywave. d. Diversity ans: d- What do you call the gigantic emissions of hydrogen from the sun? a. Solar flares b. SIDs c. Kennely-Heaviside d. Sun spots ans: a- Sudden ionospheric disturbance. a. Solar flares b. SIDs c. Sun spots d. Intertropical convergence ans: b- A means of beyond the line of sight propagation of UHF signals. a. Microwave propagation b. Space wave propagation c. Troposcatter propagation d. Surface wave propagation ans: c- Two directional antennas are pointed so that their beams intersect in the troposphere. a. Skywave b. Surface wave c. Microwave d. Troposcatter ans: d- Super refraction. a. Ducting b. Troposcatter c. Skywave d. Space wave ans: a- A layer of warm air trapped above cooler air. a. Troposphere b. SID c. Duct d. Huygen's principle ans: c- Corresponds to voltage. a. electric field b. magnetic field c. gyro d. direction of propagation ans: a- Absence of reception. a. Skip distance b. Maximum usable c. Shadow zone d. Twilight zone ans: c- Each point on a spherical waveform maybe a source of a secondary spherical wavefront. a. Snell's law b. Huygen's principle c. Rayleigh's principle d. De Morgan's theorem ans: b- Ducting occurs in which region of the atmosphere? a. Stratosphere b. Troposphere c. Ionosphere d. Ozone layer ans: b- When is the E region most ionized? a. At midday b. At midnight c. At dusk d. At dawn ans: a- Transequatorial propagation is best during a. night time b. afternoon or early evening c. noontime d. morning ans: b- Which of the following is most affected by knife-edge refraction? a. Very high and Ultra high frequencies b. High frequency c. Medium Frequency d. Low Frequency ans: a- Which ionosphere layer has an average height of 225 km at night? a. D layer b. E layer c. F1 layer d. F2 layer ans: d