Technicians Exam-Radio Waves

Card Set Information

Author:
rledwith
ID:
221464
Filename:
Technicians Exam-Radio Waves
Updated:
2013-06-13 12:25:10
Tags:
rdl tech exam t3
Folders:

Description:
Amateur Radio Technicians Exam - T3 Question Set - Radio Waves
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user rledwith on FreezingBlue Flashcards. What would you like to do?


  1. 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?
    A. Change the batteries in your radio to a different type
    B. Turn on the CTCSS tone
    C. Ask the other operator to adjust his squelch control
    D. Try moving a few feet, as random reflections may be causing multi-path distortion
    • D. Try moving a few feet, as random reflections may be causing multi-path distortion
    • In a location where reflections can occur, such as near vehicles or buildings, it is possible for a direct signal and a reflected signal to interfere with each other at the receiver and partially cancel. When this occurs, all that is necessary is to move approximately one-half wavelength in any direction — about three feet on the 2 meter band. It is likely that you’ll find a “hot spot” within that range, or at least a location where the cancellation is greatly reduced. [Ham Radio License Manual, page 4-2]
  2. T3A02 Why are UHF signals often more effective from inside buildings than VHF signals?
    A. VHF signals lose power faster over distance
    B. The shorter wavelength allows them to more easily penetrate the structure of buildings
    C. This is incorrect; VHF works better than UHF inside buildings
    D. UHF antennas are more efficient than VHF antennas
    • B. The shorter wavelength allows them to more easily penetrate the structure of buildings
    • Radio waves can penetrate openings in otherwise solid objects as long as at least one side of the opening is longer than about one-half wavelength. For this reason, the shorter wavelengths of UHF signals make them more effective at propagating into and out of buildings in urban areas. Larger obstructions also diffract or bend signals better, so UHF signals also have less shadowing effects in urban areas. [Ham Radio License Manual, page 4-1]
  3. T3A03 What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands?
    A. Right-hand circular
    B. Left-hand circular
    C. Horizontal
    D. Vertical
    • C. Horizontal
    • Horizontally polarized Yagis and quads are usually used for long-distance communications, especially for “weak signal” SSB and CW contacts on the VHF and UHF bands. Horizontal polarization is preferred because it results in lower ground losses when the wave reflects from or travels along the ground. [Ham Radio License Manual, page 4-15]
  4. 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?
    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
    • B. Signals could be significantly weaker
    • On the VHF and UHF bands, it is important to keep the transmitting and receiving antennas aligned so that they have matching polarizations. If the radio wave from a transmitter arrives at the receiver with a different polarization, the receiving antenna does not respond as well to the incoming radio wave. Since most repeaters have vertically polarized antennas, when using a low-power handheld radio to access a repeater it is important that your antenna be vertically polarized, too. [Ham Radio License Manual, page 4-6]
  5. T3A05 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?
    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
    • B. Try to find a path that reflects signals to the repeater
    • Remember that buildings and hills can act as radio reflectors. If you can “aim” your signal at one of these large reflectors, it is often possible for your signal to avoid an obstruction directly in your line of sight to the desired station. [Ham Radio License Manual, page 4-14]
  6. T3A06 What term is commonly used to describe the rapid fluttering sound sometimes heard from mobile stations that are moving while transmitting?      
    A. Flip-flopping
    B. Picket fencing
    C. Frequency shifting
    D. Pulsing
    • B. Picket fencing
    • Imagine yourself driving through an area with lots of reflection. You will travel in and out of “hot spots” and “dead spots” quite rapidly. The effect on your signal is an equally rapid increase and decrease in signal strength called mobile flutter or picket fencing. [Ham Radio License Manual, page 4-2]
  7. T3A07 What type of wave carries radio signals between transmitting and receiving stations?
    A. Electromagnetic
    B. Electrostatic
    C. Surface acoustic
    D. Magnetostrictive
    • A. Electromagnetic
    • An electromagnetic wave is a combination of an electric and a magnetic field, just like the fields in a capacitor and inductor but spreading out into space like ripples traveling across the surface of water. The wave’s electric and magnetic fields oscillate at the same frequency as the RF current in the transmitting antenna. [Ham Radio License Manual, page 4-6]
  8. T3A08 What is the cause of irregular fading of signals from distant stations during times of generally good reception?
    A. Absorption of signals by the “D” layer of the ionosphere
    B. Absorption of signals by the “E” layer of the ionosphere
    C. Random combining of signals arriving via different path lengths
    D. Intermodulation distortion in the local receiver
    • C. Random combining of signals arriving via different path lengths
    • Any time signals can take more than one path from the transmitter to the receiver, it is possible that they will partially cancel, causing the combined signals to fade out. This can occur on any band, although it is more common on the HF bands because of variations in the ionosphere. [Ham Radio License Manual, page 4-2]
  9. T3A09 Which of the following is a common effect of “skip” reflections between the Earth and the ionosphere?
    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
    • B. The polarization of the original signal is randomized
    • The characteristics of the ionosphere vary with solar radiation, whether it is day or night, or from different concentrations of molecules and ions. As a result, as a radio wave travels through the ionosphere its polarization often changes randomly so that when received, it can have any polarization. [Ham Radio License Manual, page 4-6]
  10. T3A10 What may occur if VHF or UHF data signals propagate over multiple paths?
    A. Transmission rates can be increased by a factor equal to the number of separate paths observed
    B. Transmission rates must be decreased by a factor equal to the number of separate paths observed
    C. No significant changes will occur if the signals are transmitting using FM
    D. Error rates are likely to increase
    • D. Error rates are likely to increase
    • Variations in signal strength from multipath that cause fading of voice signals can also cause digital data signals to be received with a higher error rate, particularly at VHF and UHF. (See question T3A06.) [Ham Radio License Manual, page 4-2] *T3A06 - Imagine yourself driving through an area with lots of reflection. You will travel in and out of “hot spots” and “dead spots” quite rapidly. The effect on your signal is an equally rapid increase and decrease in signal strength called mobile flutter or picket fencing. [Ham Radio License Manual, page 4-2]
  11. T3A11 Which part of the atmosphere enables the propagation of radio signals around the world?
    A. The stratosphere
    B. The troposphere
    C. The ionosphere
    D. The magnetosphere
    • C. The ionosphere
    • Radio waves at HF (and sometimes VHF) can be completely bent back towards the earth by diffraction in the ionosphere’s F-layers as if they were reflected. This is called sky wave propagation or skip. Since the Earth’s surface is also conductive, it can also reflect radio waves. This means that a radio wave can be reflected between the ionosphere and ground multiple times. Each reflection from the ionosphere is called a hop and allows radio waves to be received hundreds or thousands of miles away. This is the most common way for hams to make long-distance contacts on the HF bands. [Ham Radio License Manual, page 4-3]
  12. T3B01 What is the name for the distance a radio wave travels during one complete cycle?
    A. Wave speed
    B. Waveform
    C. Wavelength
    D. Wave spread
    • C. Wavelength
    • A radio wave travels at a constant speed, the speed of light. That means the radio wave will always cover the same distance during the time it takes the wave’s oscillating electric and magnetic fields to make one complete cycle. That distance is the wave’s wavelength. All radio waves of the same frequency, traveling at the speed of light, will have the same wavelength. [Ham Radio License Manual, page 2-4]
  13. T3B02 What term describes the number of times per second that an alternating current reverses direction?
    A. Pulse rate
    B. Speed
    C. Wavelength
    D. Frequency
    • D. Frequency
    • One complete sequence of alternating current (ac) flowing in one direction, stopping, reversing, and stopping again is a cycle. The number of cycles per second is the ac current’s frequency. This also describes the frequency of a radio signal or wave. [Ham Radio License Manual, page 3-6]
  14. T3B03 What are the two components of a radio wave?
    A. AC and DC
    B. Voltage and current
    C. Electric and magnetic fields
    D. Ionizing and non-ionizing radiation
    • C. Electric and magnetic fields
    • An electromagnetic wave is a combination of an electric and a magnetic field, just like the fields in a capacitor and inductor but spreading out into space like ripples traveling across the surface of water. The wave’s electric and magnetic fields oscillate at the same frequency as the RF current in the transmitting antenna. [Ham Radio License Manual, page 4-6]
  15. T3B04 How fast does a radio wave travel through free space?
    A. At the speed of light
    B. At the speed of sound
    C. Its speed is inversely proportional to its wavelength
    D. Its speed increases as the frequency increases
    • A. At the speed of light
    • All electromagnetic energy — radio waves, light, X-rays — travels at the speed of light. In a vacuum, the speed of light (represented by a lower-case c) is 300,000,000 meters per second. It travels close to that speed in air. In denser materials such as water or glass, and in cables, light travels slower. [Ham Radio License Manual, page 2-4]
  16. T3B05 How does the wavelength of a radio wave relate to its frequency?
    A. The wavelength gets longer as the frequency increases
    B. The wavelength gets shorter as the frequency increases
    C. There is no relationship between wavelength and frequency
    D. The wavelength depends on the bandwidth of the signal
    • B. The wavelength gets shorter as the frequency increases
    • Because radio waves travel at a constant speed, the higher their frequency, the less time it takes to complete one cycle, and the less distance it has traveled during that cycle — its wavelength. Higher frequencies mean shorter wavelengths and vice versa. (See question T3A01) [Ham Radio License Manual, page 2-5] *T3A01 - In a location where reflections can occur, such as near vehicles or buildings, it is possible for a direct signal and a reflected signal to interfere with each other at the receiver and partially cancel. When this occurs, all that is necessary is to move approximately one-half wavelength in any direction — about three feet on the 2 meter band. It is likely that you’ll find a “hot spot” within that range, or at least a location where the cancellation is greatly reduced. [Ham Radio License Manual, page 4-2]
  17. T3B06 What is the formula for converting frequency to wavelength in meters?
    A. Wavelength in meters equals frequency in hertz multiplied by 300
    B. Wavelength in meters equals frequency in hertz divided by 300
    C. Wavelength in meters equals frequency in megahertz divided by 300
    D. Wavelength in meters equals 300 divided by frequency in megahertz
    • D. Wavelength in meters equals 300 divided by frequency in megahertz
    • The key to remembering this relationship is that wavelength and frequency are inversely proportional. That is, as one gets larger, the other must get smaller. The formula that describes this relationship is: Wavelength (l, in meters) = 300 / (Frequency (f) in MHz). [Ham Radio License Manual, page 2-5]
  18. T3B07 What property of radio waves is often used to identify the different frequency bands?
    A. The approximate wavelength
    B. The magnetic intensity of waves
    C. The time it takes for waves to travel one mile
    D. The voltage standing wave ratio of waves
    • A. The approximate wavelength
    • Because of the radio wave’s constant velocity (see question T3A01), knowing a radio wave’s wavelength is the same as knowing its frequency and vice versa. By referring to a frequency band by approximate wavelength, which is traditional, the frequency range is also implied. [Ham Radio License Manual, page 2-5] *T3A01 - In a location where reflections can occur, such as near vehicles or buildings, it is possible for a direct signal and a reflected signal to interfere with each other at the receiver and partially cancel. When this occurs, all that is necessary is to move approximately one-half wavelength in any direction — about three feet on the 2 meter band. It is likely that you’ll find a “hot spot” within that range, or at least a location where the cancellation is greatly reduced. [Ham Radio License Manual, page 4-2]
  19. T3B08 What are the frequency limits of the VHF spectrum?
    A. 30 to 300 kHz
    B. 30 to 300 MHz
    C. 300 to 3000 kHz
    D. 300 to 3000 MHz
    • B. 30 to 300 MHz
    • See the table of RF Spectrum Ranges. [Ham Radio License Manual, page 2-3]
  20. T3B09 What are the frequency limits of the UHF spectrum?
    A. 30 to 300 kHz
    B. 30 to 300 MHz
    C. 300 to 3000 kHz
    D. 300 to 3000 MHz
    • D. 300 to 3000 MHz
    • See the table of RF Spectrum Ranges. [Ham Radio License Manual, page 2-3]
  21. T3B10 What frequency range is referred to as HF?
    A. 300 to 3000 MHz
    B. 30 to 300 MHz
    C. 3 to 30 MHz
    D. 300 to 3000 kHz
    • C. 3 to 30 MHz
    • See the table of RF Spectrum Ranges. [Ham Radio License Manual, page 2-3]
  22. T3B11 What is the approximate velocity of a radio wave as it travels through free space?
    A. 3000 kilometers per second
    B. 300,000,000 meters per second
    C. 300,000 miles per hour
    D. 186,000 miles per hour
    • B. 300,000,000 meters per second
    • All electromagnetic energy — radio waves, light, X-rays — travels at the speed of light. In a vacuum, the speed of light (represented by a lower-case c) is 300,000,000 meters per second. It travels close to that speed in air. In denser materials such as water or glass, and in cables, light travels slower. [Ham Radio License Manual, page 2-4]
  23. T3C01 Why are “direct” (not via a repeater) UHF signals rarely heard from stations outside your local coverage area?
    A. They are too weak to go very far
    B. FCC regulations prohibit them from going more than 50 miles
    C. UHF signals are usually not reflected by the ionosphere
    D. They collide with trees and shrubbery and fade out
    • C. UHF signals are usually not reflected by the ionosphere
    • The ability of the ionosphere to diffract or bend radio waves also depends on the frequency of the radio wave. Higher frequency waves are bent less than those of lower frequencies. At VHF and higher frequencies the waves usually pass through the ionosphere with only a little bending and are lost to space. This is why VHF and UHF signals from stations beyond the radio horizon are rarely heard without being relayed by a repeater. [Ham Radio License Manual, page 4-4]
  24. T3C02 Which of the following might be happening when VHF signals are being received from long distances?
    A. Signals are being reflected from outer space
    B. Signals are arriving by sub-surface ducting
    C. Signals are being reflected by lightning storms in your area
    D. Signals are being refracted from a sporadic E layer
    • D. Signals are being refracted from a sporadic E layer
    • At all points in the solar cycle, patches of the ionosphere’s E-layer can become sufficiently ionized to reflect VHF signals back to earth. Most common on the 6 meter and 2 meter bands, sporadic-E propagation occurs from reflections off highly ionized patches in the ionosphere’s E-layer. The patches form at irregular intervals and places, earning them the name “sporadic.” Sporadic-E propagation can relay signals as far as 1500 miles. [Ham Radio License Manual, page 4-4]
  25. T3C03 What is a characteristic of VHF signals received via auroral reflection?
    A. Signals from distances of 10,000 or more miles are common
    B. The signals exhibit rapid fluctuations of strength and often sound distorted
    C. These types of signals occur only during winter nighttime hours
    D. These types of signals are generally strongest when your antenna is aimed to the south (for stations in the Northern Hemisphere
    • B. The signals exhibit rapid fluctuations of strength and often sound distorted
    • The aurora (northern lights) is the glow from thin sheets of charged particles flowing down through the lower layers of the ionosphere. Those thin sheets 50 miles or more above the Earth’s surface reflect VHF and UHF signals. Because the aurora is constantly changing, the reflected signals change strength quickly and are often distorted. [Ham Radio License Manual, page 4-4]
  26. 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?
    A. Backscatter
    B. Sporadic E
    C. D layer absorption
    D. Gray-line propagation
    • B. Sporadic E
    • At all points in the solar cycle, patches of the ionosphere’s E-layer can become sufficiently ionized to reflect VHF signals back to earth. Most common on the 6 meter and 2 meter bands, sporadic-E propagation occurs from reflections off highly ionized patches in the ionosphere’s E-layer. The patches form at irregular intervals and places, earning them the name “sporadic.” Sporadic-E propagation can relay signals as far as 1500 miles. [Ham Radio License Manual, page 4-4]
  27. T3C05 What is meant by the term “knife-edge” propagation?
    A. Signals are reflected back toward the originating station at acute angles
    B. Signals are sliced into several discrete beams and arrive via different paths
    C. Signals are partially refracted around solid objects exhibiting sharp edges
    D. Signals propagated close to the band edge exhibiting a sharp cutoff
    • C. Signals are partially refracted around solid objects exhibiting sharp edges
    • Radio waves can be reflected by any sudden change in the medium through which they are traveling, such as a building, hill or even weather-related changes in the atmosphere. Obstructions such as buildings and hills create radio shadows, especially at VHF and UHF frequencies. The figure shows how radio waves can also be diffracted or bent as they travel past sharp edges of these objects. This is called knife-edge propagation. [Ham Radio License Manual, page 4-1]
  28. T3C06 What mode is responsible for allowing over-the-horizon VHF and UHF communications to ranges of approximately 300 miles on a regular basis?
    A. Tropospheric scatter
    B. D layer refraction
    C. F2 layer refraction
    D. Faraday rotation
    • A. Tropospheric scatter
    • Propagation at and above VHF frequencies assisted by atmospheric phenomena such as weather fronts or temperature inversions is called tropospheric scatter propagation or just “tropo.” Layers of air with different characteristics can also form structures called ducts that can guide even microwave signals for long distances. Tropo is regularly used by amateurs to make VHF and UHF contacts that would otherwise be impossible by line-of-sight propagation. Tropo contacts over 300-mile paths are not uncommon. [Ham Radio License Manual, page 4-2]
  29. T3C07 What band is best suited to communicating via meteor scatter?
    A. 10 meters
    B. 6 meters
    C. 2 meters
    D. 70 cm
    • B. 6 meters
    • A meteoroid burning up in the upper atmosphere leaves a trail of ionized gas lasting up to several seconds that can reflect radio signals. Bouncing signals off of these ionized trails is called meteor scatter propagation. 6 meters is the best band for meteor scatter and contacts can be made at distances up to 1200 to 1500 miles. [Ham Radio License Manual, page 4-5]
  30. T3C08 What causes “tropospheric ducting”?
    A. Discharges of lightning during electrical storms
    B. Sunspots and solar flares
    C. Updrafts from hurricanes and tornadoes
    D. Temperature inversions in the atmosphere
    • D. Temperature inversions in the atmosphere
    • Propagation at and above VHF frequencies assisted by atmospheric phenomena such as weather fronts or temperature inversions is called tropospheric scatter propagation or just “tropo.” Layers of air with different characteristics can also form structures called ducts that can guide even microwave signals for long distances. Tropo is regularly used by amateurs to make VHF and UHF contacts that would otherwise be impossible by line-of-sight propagation. Tropo contacts over 300-mile paths are not uncommon. [Ham Radio License Manual, page 4-2]
  31. T3C09 What is generally the best time for long-distance 10 meter band propagation?
    A. During daylight hours
    B. During nighttime hours
    C. When there are coronal mass ejections
    D. Whenever the solar flux is low
    • A. During daylight hours
    • The highest frequency signal that can be reflected back to a point on the earth is the maximum usable frequency (MUF) between the transmitter and receiver. The lowest frequency that can travel between those points without being absorbed is the lowest usable frequency (LUF). (See the figure below.) The MUF rises as the sun illuminates the ionosphere. That’s why the upper HF bands, such as 10 meters, are more likely to be open during the day. [Ham Radio License Manual, page 4-4]
  32. T3C10 What is the radio horizon?
    A. The distance at which radio signals between two points are effectively blocked by the curvature of the Earth
    B. The distance from the ground to a horizontally mounted antenna
    C. The farthest point you can see when standing at the base of your antenna tower
    D. The shortest distance between two points on the Earth’s surface
    • A. The distance at which radio signals between two points are effectively blocked by the curvature of the Earth
    • Since most propagation at VHF and UHF frequencies is line-of-sight, the limit of the range of these signals is determined by the radio horizon. (There is some slight bending of radio waves along the Earth’s surface, so the radio horizon is slightly more distant than the visual horizon.) Increasing the height of either the transmitting or receiving antennas also increases the radio horizon’s distance. [Ham Radio License Manual, page 4-1]
  33. T3C11 Why do VHF and UHF radio signals usually travel somewhat farther than the visual line of sight distance between two stations?
    A. Radio signals move somewhat faster than the speed of light
    B. Radio waves are not blocked by dust particles
    C. The Earth seems less curved to radio waves than to light
    D. Radio waves are blocked by dust particles
    • C. The Earth seems less curved to radio waves than to light
    • Diffraction makes the Earth seem less curved to VHF and UHF radio waves than light. This allows VHF and UHF signals to travel farther than the visual line-of-sight horizon. (See question T3C10) [Ham Radio License Manual, page 4-1] *T3C10 - Since most propagation at VHF and UHF frequencies is line-of-sight, the limit of the range of these signals is determined by the radio horizon. (There is some slight bending of radio waves along the Earth’s surface, so the radio horizon is slightly more distant than the visual horizon.) Increasing the height of either the transmitting or receiving antennas also increases the radio horizon’s distance. [Ham Radio License Manual, page 4-1]

What would you like to do?

Home > Flashcards > Print Preview