Term
| What happens to the electrons inside an antenna when a radio wave encounters a receiving antenna? |
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Definition
| The electrons oscillate back and forth in step with the radio wave. |
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Term
| What term describes when new waves, created by oscillating electrons, reflect or scatter? |
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Definition
| Electromagnetic scattering |
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Term
| How does a vertical transmitting antenna radiate? |
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Definition
| Equally in all directions |
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Term
| Which antenna characteristic best describes when an antenna transfers energy equally, regardless of whether it is transmitting or receiving? |
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Definition
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Term
| Name the two fields that make up the electromagnetic field of a radio signal path. |
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Definition
| E Field (electrical) and H field (magnetic). |
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Term
| How are the E field and F field arranged towards each other and to the direction of travel? |
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Definition
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Term
| Why is a resonant antenna highly efficient? |
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Definition
| Because almost the entire signal fed to the antenna radiates. |
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Term
| What term describes when the signal power from a resonant antenna outside of its bandwidth is reflected or turned back? |
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Definition
| Standing wave ratio (SWR). |
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Term
| What device is inserted between a transmitter and the antenna and makes the transmitter think it is connected to a low SWR antenna? |
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Definition
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Term
| What is the take-off angle of an antenna? |
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Definition
| The angle above the horizon that an antenna radiates the largest amount of energy. |
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Term
| What are the two principal paths that radio waves travel? |
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Definition
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Term
| What part of the atmosphere has the most impact on sky-wave propagation? |
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Definition
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Term
| List the three components of a ground wave. |
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Definition
| Direct wave; Ground reflective wave; surface wave. |
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Term
| What do you call radio transmissions that depend on the ionosphere to provide signal paths between the transmitter and receiver? |
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Definition
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Term
| Explain the difference between a skip zone and the skip distance. |
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Definition
| Skip zone is the distance between the end of the ground portion of the circuit and the refracted signal coming back to Earth. Skip distance is the ground distance between the radiating or transmitting antenna and the point where the wave first returns to Earth. |
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Term
| What happens when sky waves and ground waves are received at the same time? |
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Definition
| The sky-wave alternately reinforces and cancels the ground-wave component causing severe signal blasting and fading. |
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Term
| What region of the ionosphere is used for HF communication during the day? |
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Definition
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Term
| What are two critical characteristics of the ionosphere that affect radio frequencies? |
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Definition
| Critical frequency and critical angle. |
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Term
| How are predictions made to determine the maximum usable frequency (MUF) and the lowest usable frequency (LUF)? |
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Definition
| By averaging long-range observations without considering day-to-day fluctuations. |
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Term
| What happens to the wave if the operating frequency is above the maximum usable frequency for a desired distance? |
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Definition
| Communication is impossible and the wave passes through the ionosphere into space or returns to Earth at a greater distance than desired. |
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Term
| What does the term lowest usable frequency (LUF) mean? |
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Definition
| When the signal just overrides the level of atmospheric and other radio noise as the frequency for transmission over any given sky-wave path is increased. |
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Term
| What makes the UHF band LOS reception very satisfactory for use? |
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Definition
| The lack of static and fading. |
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Term
| What characteristic of polarization increases energy from a desired location and reduces reception from other directions? |
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Definition
| Directional or uni-directional design. |
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Term
| What determines the polarization of a radiated wave? |
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Definition
| The direction of the lines of force making up the electric field. |
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Term
| What frequencies make little difference if you use either horizontal or vertical polarization? |
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Definition
| High frequencies with sky-wave transmission. |
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Term
| What type of antenna should you use to communicate with a moving vehicle? |
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Definition
| Vertical half-wave (omni-directional). |
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Term
| Which type of antenna polarization works better in urban areas? Why? |
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Definition
| Vertical because there is less interference due to strong television and FM radio station reception. |
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Term
| Which type of antenna polarization works better near a dense forest? Why? |
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Definition
| Horizontally because they suffer less loss than vertical ones and small changes in an antenna location don't cause large variations in the field intensity of horizontally polarized waves when antennas are located among trees or buildings. |
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Term
| How can a vertical quarter-wavelength antenna be made into a half-wavelength antenna without changing its length? |
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Definition
| By using Earth as a ground to reflect a large amount of energy radiated downward from an antenna mounted over it. |
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Term
| What is especially important when you are selecting a ground? |
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Definition
| That is has a high of a conductivity as possible to reduce ground losses and provide the best possible reflecting surface. |
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Term
| When you cannot use the actual ground, what can you use to replace it? |
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Definition
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Term
| What is a good technique to use when planning a site to place your antenna? |
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Definition
| Select a primary and alternate site. |
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Term
| List a hindrance and a benefit of transmitting and receiving around man-made obstructions. |
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Definition
| Buildings can hinder transmission and reception. However, you can use these buildings for camouflaging you antenna from the enemy. |
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Term
| When you repair an antenna, how long should you make the antenna wire in relation to the original antenna? |
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Definition
| As close to the original antenna length as possible. |
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Term
| What is the most important rule when working on any type of antenna? |
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Definition
| Never touch an antenna connected to a transmitter. |
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Term
| On a solid core whip antenna, what should you do to ensure a good electrical connection? |
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Definition
| Clean the area around the break. |
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Term
| What must you use if you have to replace a guy rope with a piece of wire? |
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Definition
| Connect the short pieces with insulators, so antenna operations are not affected. |
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Term
| What is the formula to calculate the physical length of an antenna for a 7 MHz frequency? |
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Definition
Length in meters:
150x0.95/MHz=142.5/7 MHz
Length in feet:
492x0.95/Freq in MHz=468/7 MHz |
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Term
| Name the two types of transmission lines. |
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Definition
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Term
| Which type of transmission line is a coaxial cable? |
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Definition
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Term
| At what frequency ranges are insulators more important? |
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Definition
| VHF, UHF, and frequencies above 30 MHz. |
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Term
| Realized by maximum gain when it is used with transmitter and receiver antennas. |
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Definition
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Term
| One consideration is land space. |
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Definition
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Term
| Determined by the operational requirement. |
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Definition
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Term
| To use several, a separate antenna is required. |
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Definition
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Term
| Angle of radiation required. |
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Definition
| Distance between stations. |
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Term
| Without it, this becomes an inefficient radiator. |
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Definition
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Term
| A substitute antenna may be required. |
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Definition
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Term
| What two main categories of antenna usage are determined by the operational requirement? |
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Definition
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Term
| What type of antenna does ground-to-air communications require? |
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Definition
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Term
| Why do tactical situations mostly use vertical antennas? |
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Definition
| Ease of installation and smaller real estate required. |
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Term
| What is a good safety measure to use when erecting an antenna near power lines? |
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Definition
| Use a distance three times the length of the antenna for separation between the antenna and power lines. |
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Term
| What safety cardinal rule should you follow when working with high voltage equipment? |
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Definition
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Term
| What can still occur even when an antenna is tied down and radiation efficiency is reduced? |
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Definition
| Limited communications range. |
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Term
| How does the direction a vehicle faces affect the radiated circuit of a whip antenna? |
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Definition
| Perpendicular across the vehicle when it's connected to the right rear of the vehicle. |
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Term
| What type of polarization does the whip antenna use? |
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Definition
| Vertical under normal operating conditions. |
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Term
| What is the radiation pattern of the inverted Vee antenna? |
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Definition
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Term
| What is the take-off angle of the NVIS antenna? |
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Definition
| High, at 60 to 90 degrees, and almost vertical. |
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Term
| What is the NVIS' antenna directivity? |
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Definition
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Term
| Name two advantages to using a dipole antenna. |
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Definition
| It is easy to transport and presents a low visual profile. |
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Term
| What formula determines the physical length of a half wave dipole antenna? |
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Definition
| Divide 468 by the frequency in MHz. |
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Term
| What type of effect does using a dipole antenna without a balun produce? |
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Definition
| Causes the coaxial cable shield to radiate which skews the radiation pattern. |
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Term
| Which antenna combines vertical and horizontal wire sections? |
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Definition
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Term
| How is the inverted L antenna polarized? |
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Definition
| Horizontal from the horizontal section and vertical from the vertical section. |
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Term
| What must you do when making a long wire antenna for lone-range sky-wave propagation? |
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Definition
| Make the antenna as long as possible. |
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Term
| What size wire should be used for a long wire antenna? |
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Definition
| At least AWG number 12 or larger. |
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Term
| When using a terminating resistor on a long wire antenna, which direction does the antenna become uni-directional? |
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Definition
| Toward the resistor's terminating end. |
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Term
| Which direction do you orient the lower end of a sloping long wire antenna? |
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Definition
| Towards the receiving station. |
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Term
| Why is the "Vee" antenna used extensively for long-range tactical use? |
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Definition
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Term
| For reasonable performance, how long should a sloping "Vee" antenna be? |
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Definition
| At least one, but preferably several wavelengths long. |
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