# Shared Flashcard Set

## Details

Communications Exam 1
Homework questions.
26
Engineering
05/15/2006

## Additional Engineering Flashcards

Term
 State the purpose of a transmission line.
Definition
 The purpose of a transmission line is transfer energy from a source to a load by electronic means.
Term
 What are the two basic types of transmission lines?
Definition
 The two basic types of transmission lines are balanced and unbalanced lines.
Term
 Define balanced and unbalanced lines.
Definition
 Balanced – Both wires carry RF, but voltage and current are 180 degrees out of phase. Unbalanced – One conductor is carrying the RF, the other conductor is at a different potential.
Term
 Define balanced and unbalanced lines.
Definition
 Balanced – Both wires carry RF, but voltage and current are 180 degrees out of phase. Unbalanced – One conductor is carrying the RF, the other conductor is at a different potential.
Term
 Calculate the wavelengths for lines 1 km long operated at (a) 1 kHz, (b) 50 kHz, and (c) 7.5 MHz.
Definition
 a. 300,000 meters. b. 6,000 meters. c. 40 meters.
Term
 Explain the concepts of source and load.
Definition
 Source is anything that generates energy. Referred to as a repeater or transmitter. A load is anything that consumes energy.
Term
 Explain the concept of traveling waves.
Definition
 Traveling waves are any RF that is connected or applied to a transmission line.
Term
 What is meant by a properly terminated line?
Definition
 A properly terminated line is all of the energy from a source is absorbed by the load. All the energy is transferred by the transmission line.
Term
 Define resonant line.
Definition
 Resonant line – A transmission line that is not properly terminated.
Term
 Explain how standing waves are formed.
Definition
 Standing waves are formed by any RF energy that is not consumed by the load will return to the source.
Term
 Explain how standing waves are formed.
Definition
 Standing waves are formed by any RF energy that is not consumed by the load will return to the source.
Term
 What device is used to measure SWR on a coaxial cable?
Definition
 To measure SWR on a coaxial cable, a Wattmeter is used.
Term
 Define characteristic impedance.
Definition
 The amount of inductance, capacitance, and resistance in a transmission line is characteristic impedance. It is determined by the diameter of the conductors or the spacing of the wire.
Term
 List and describe the three major types of losses for transmission lines.
Definition
 The three major types of losses for transmission lines are copper losses, dielectric losses, and radiation losses.
Term
 Briefly describe the three classifications of radio wave propagation.
Definition
 1. Ground wave – RF travels along surface of earth. Direct wave – RF travels from transmitter to receiver. Sky wave – RF sent from earth, reflects of atmosphere, and back to earth to the receiver.
Term
 How can ground wave coverage by increased?
Definition
 Ground wave coverage can be increased by using vertical polarization.
Term
 How can the range of space wave transmissions be increased?
Definition
 The range of space (direct) wave transmissions can be increased by increasing the height of either the transmission or receiving antennas.
Term
 Define radio horizon and explain how it occurs.
Definition
 Radio horizon – Any RF that travels further than your visible horizon. It occurs because the RF curves along with the surface of the earth.
Term
 For long distance communications, which of the wave propagation classifications is used most?
Definition
 For long distance communications, sky wave propagation is used most.
Term
 Define (a) critical frequency (b) critical angle.
Definition
 a. Critical frequency – Highest frequency of the RF that will still reflect off the atmosphere. MUF b. Critical angle – Highest angle that can still be reflected back to earth.
Term
 Explain the concept of multiple-hop transmission.
Definition
 Multiple hop transmission is when the RF reflects off the atmosphere and back to earth multiple times. Six times to make one complete revolution around earth.
Term
 How can skip distance be maximized?
Definition
 Skip distance can be maximized by increasing the frequency and decreasing the angle.
Term
 Describe the effects of multipath reception.
Definition
 The effects of multipath reception are fading and interference.
Term
 Describe the four categories of variations that affect the ionosphere.
Definition
 The four categories of variations that affect the ionosphere are diurnal, geographical, cyclical, and seasonal.
Term
 How can the range of communications in the VHF, UHF, and higher frequencies be extended?
Definition
 A satellite and tropospheric scatter can extend the range of communications in the VHF, UHF, and higher frequencies.
Term
 Explain the concept of tropospheric scatter.
Definition
 Tropospheric scatter is the use of RF that reflects off the troposphere, but most of the energy is scattered in other directions.
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