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NAVEDTRA 14182
WAVE PROPOGATION, TRANSMISSION LINES, AND ANTENNAS
| Question | Answer |
|---|---|
| Which two basic fields are associated with every antenna? | induction and radiation |
| Which field is associated with the energy stored in the antenna? | induction |
| Which type of antenna has an electrical length equal to half the wavelength of the signal being transmitted? | half-wave |
| What is an energy wave called that is generated by a transmitter? | radio wave |
| What is the basic shape of the wave generated by a transmitter? | sine wave |
| The frequencies falling between 3kHz and what are called radio frequencies since they are commonly used in radio communications? | 300GHz |
| The usable radio frequency range is roughly 10kHz to what? | 100GHz |
| What is the VLF frequency range? | 3 to 30kHz |
| What is the LF frequency range? | 30 to 300kHz |
| What is the MF frequency range? | 300 to 3000kHz |
| What is the HF frequency range? | 3 to 30 MHz |
| What is the VHF frequency range? | 30 to 300MHz |
| What is the UHF frequency range? | 300 to 3000MHz |
| What is the SHF frequency range? | 3 to 30GHz |
| What is the EHF frequency range? | 30 to 300GHz |
| Any frequency that is a whole number multiple of a smaller basic frequency is known as what property of that basic frequency? | Harmonic |
| What is the property of a radio wave which is simply the amount of time required for the completion of one full cycle? | period |
| What is the space called occupied by one full cycle of a radio wave at any given time? | wavelength |
| Where must the receiving antenna be located for maximum absorption of energy from the electromagnetic fields? | plane of polarization |
| Troposphere, stratosphere, along with what else are the three separate regions or layers that the Earth's atmosphere is divided into? | ionosphere |
| Which atmosphere layer has relatively little effect on radio waves because it is a relatively calm region with little or no temperature changes? | stratosphere |
| What is the most important region of the atmosphere for long distance point-to-point communications? | ionosphere |
| What are the two principle ways in which electromagnetic (radio) energy travels from a transmitting antenna to a receiving antenna? | ground and sky waves |
| Which frequency band is used for sky wave propagation? | high frequency (HF) |
| What is the process known as of upsetting electrical neutrality? | ionization |
| What occurs when the free electrons and positive ions collide with each other? | recombination |
| How many layers is the ionosphere composed of? | 3 |
| Each ionospheric layer has a maximum frequency at which radio waves can be transmitted vertically and refracted back to earth which is known as what? | absorption |
| In what practice are two transmitters and two receivers used, each pair tuned to a different frequency, with the same information being transmitted simultaneously over both frequencies? | frequency diversity |
| There is little natural interference above what frequency? | 30MHz |
| What are responsible for variations in the ionization level of the ionosphere? | sunspots |
| Long distance propagation of HF radio waves is almost totally "blanked out" when what occurs? | sudden ionospheric disturbance (SID) |
| For a given angle of incidence and time of day, there is maximum frequency that can be used for communications between two given locations. What is this frequency called? | maximum usable frequency (MUF) |
| Fog can cause serious attenuation by absorption at frequencies above what? | 2 GHz |
| What is the condition when layers of warm air are formed above layers of cool air known as? | temperature inversion |
| As the lowest region of the earth's atmosphere, the troposphere extends from the earth's surface to a height of slightly over how many miles? | 7 mi |
| What region does virtually all weather phenomena occur in? | troposphere |
| The usable frequency range for tropospheric scattering is from about 100MHz to what? | 10GHz |
| A correctly designed tropospheric scatter circuit will provide highly reliable service for distances ranging from 50 miles to how many miles? | 500 mi |
| Which device is designed to guide electrical energy from one point to another? | transmission line |
| Which type of line is most often used for power lines, rural telephone lines, and telegraph lines? | two-wire open |
| Which type of line consists of two insulated wires twisted together to form a flexible line without the use of spacers? | twisted pair |
| Leakage caused by the condensation of moisture is prevented in some rigid line applications by the use of what? | inert gas |
| The radius of bends in the waveguide must measure greater than how many wavelengths at the operating frequency of the equipment to avoid excess attenuation? | two |
| Line losses may be any of three types- radiation/induction, dielectric, and what else? | copper loss |
| Copper losses can be minimized and conductivity increased in an RF line by plating the line with what? | silver |
| Which type of losses occur because some magnetic lines of force about a conductor do not return to the conductor when the cycle alternates? | radiation loss |
| What determines the amount of current that can flow when a given voltage is applied to an infinitely long line? | characteristic impedance |
| The characteristic impedance of lines in actual use normally lies between 50 and how many ohms? | 600 ohms |
| When a transmission line is "short" compared to the length of the radio frequency waves it carries, the opposition presented to the input terminals is determined primarily by what? | load impedance |
| If a line is not terminated in characteristic impedance, what is it said to be? | finite |
| What are voltages called that are moving toward the receiving end of the line? | incident voltages |
| Which type of line has no standing waves of current and voltage? | nonresonant |
| What is the ratio of maximum voltage to minimum voltage on a line called? | VSWR |
| What are hollow metal tubes used to transfer energy from one point to another? | waveguides |
| Which two basic classifications are most practical transmitting antennas divided into? | Hertz and Marconi |
| Which type of antennas operate with one end grounded and are mounted perpendicular to the earth or to a surface acting as a ground? | Marconi |
| Hertz antennas are generally used for frequencies above what? | 2 MHz |
| Which three parts does a complete antenna system consist of? | coupling device, feeder, and antenna |
| What is defined as a conductor or group of conductors used either for radiating electromagnetic energy into space or for collecting it from space? | antenna |
| What it the interchangeability of the same antenna for transmitting and receiving known as? | reciprocity |
| Which frequencies is sky-wave transmission used? | high frequency |
| Which type of polarization is used by VHF and UHF transmissions? | horizontal |
| What is the useful part of the transmitter's signal? | radiated energy |
| What it a plot of the radiated energy from an antenna? | radiation pattern |
| What is it known as when antenna sources radiate energy equally in all directions? | isotropic radiation |
| Which type of radiators emit stronger radiation in one direction than in another? | anisotropic |
| What is used to indicate directions of minimum radiation? | null |
| The electrical length of any antenna wire can be increased or decreased by what way? | loading |
| What is the basic unit from which many complex antennas are constructed? | half-wave antenna |
| What term is used to indicate an antenna that is very short compared with the wavelength of the operating frequency? | doublet |
| What is the simplest form of a practical antenna? | doublet |
| What type of antenna is the shortest antenna that can be used in free space? | 1/2 wavelength |
| What is an ordinary half-wave antenna that has one or more additional conductors connected across its ends? | folded dipole |
| What is a parasitic element referred to as when it operates to reinforce energy coming from the driver toward itself? | director |
| What is a parasitic element referred to as if it is placed so it causes maximum energy radiation in a direction away from itself and toward the driven element? | reflector |
| What designates an array in which the direction of maximum radiation is perpendicular to the plane containing these elements? | broadside array |
| What type of array is it when all the elements lie in a straight line with no radiation at the ends of the array? | collinear |
| What type of array is it when the principle direction of radiation is along the plane of the array and perpendicular to the elements? | end-fire |
| What is an antenna that is a wavelength or longer at the operating frequency? | long-wire |
| What is a horizontal, long-wire antenna designed especially for the reception ad transmission of low frequency, vertically polarized ground waves? | beverage antenna |
| What is a half-wave radiator with a reflector? | corner-reflector antenna |
| What is one of the most popular fixed-station antennas because it is very useful in point-to-point communications? | rhombic |
| What is the heating of an insulating material by placing it in a high frequency electric field? | dielectric heating |
| What parts of the human body are highly susceptible to dielectric heating? | eyes |
| What is the area of radiation pattern that is covered by radiation? | lobe |
Created by:
nng7294
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