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3D156 - Volume 1 > Unit 6. Transmission Lines and Antennas > Flashcards

Unit 6. Transmission Lines and Antennas Flashcards

1
Q
  1. What is line loss?

1. Define “transmission line” and give an example of one.

A
  1. A conductor or series of conductors used to carry energy from a source to a load. Examples include the flexible coaxial cable, the rigid coaxial cable, AC power cord on a stereo, a cable television wire, and a telephone cord.
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2
Q
  1. What are some of the types of transmission line loss?
A

Resistive, skin effect, radiation, induction, capacitive, and leakage.

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3
Q
  1. Name two methods of reducing induction loss.
A

The use of standoff insulators and shielded conductors.

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4
Q
  1. What are the causes of major power loss in a flexible coaxial cable?
A

The dielectric and skin effect.

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5
Q
  1. Why is there very little radiation loss in a rigid coaxial cable?
A

Because the energy is confined between the two conductors.

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6
Q
  1. Describing electrical characteristics

1. What determines ZO of a transmission line?

A

Its series inductance and shunt capacitance.

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7
Q
  1. Identify the primary determinants of a line’s capacitance.
A

The amount of capacitance is primarily determined by the size of the conductors, the space between them, plus the dielectric material.

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8
Q
  1. What does “cutoff frequency” refer to when we talk about transmission lines?
A

The frequency at which the value of XL and XC are such that the signal is developed across the series inductance and shunted by the capacitance and, thus, not passed along the line.

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9
Q
  1. Define “wavelength.”
A

The distance in space occupied by one cycle of a radio wave at any given instant.

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10
Q
  1. As signals frequency decreases, what happens to wavelength?
A

Wavelength increases.

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11
Q
  1. What is electrical length?

1. What is electrical length?

A

Comparison of physical length and wavelength expressed in number of wavelengths.

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12
Q
  1. What is the unit of measure for electrical length?
A

Meters.

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13
Q
  1. What happens to electrical length as signal frequency decreases?
A

Electrical length decreases.

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14
Q

6–2. Transmission Line Terminations

  1. Why do we have standing waves?
  2. Describe a nonresonant transmission line.
A

It is a line having no reflected waves.

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15
Q
  1. What is an incident wave?
A

Voltage and current waves as they move from source to load.

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16
Q
  1. What is a standing wave?
A

It is the vector sum of the forward and reflected waves.

17
Q
  1. Define “VSWR.”
A

This is a comparison (expressed as a ratio) of the maximum and minimum voltages found along the line.

18
Q
  1. If a transmission line has a perfect impedance match, what would the VSWR be?
A

1:1.

19
Q
  1. Terminating the line

1. What is the voltage level at an open termination?

A

Voltage will be at maximum across an open.

20
Q
  1. What is the phase relationship between forward and reflected voltage waves when the line is terminated in a short?
A

Voltage is reflected 180 degrees out of phase.

21
Q
  1. What can you use to match a 50-ohm cable to a 600-ohm antenna?
A

A balun.

22
Q
  1. Wave propagation

1. State the real limiting factor of space-wave propagation.

A

Any obstructions.

23
Q
  1. What two components make up the space wave?
A

(1) The ground-reflected wave.

(2) The direct wave.

24
Q
  1. Describe the relationship between LOS distance and antenna height.
A

LOS distance increases as antenna height increases.

25
Q
  1. Basic antenna concepts

1. Define “reciprocity.”

A

The ability of an antenna to both receive and transmit equally well.

26
Q
  1. If a wave is horizontally polarized, in what direction do the electric lines of force lie?
A

In a horizontal direction.

27
Q
  1. What is an isotropic antenna?
A

A theoretical antenna that radiates equally well in all directions.

28
Q
  1. Name the three antenna directional classifications.
A

(1) Omnidirectional.
(2) Bidirectional.
(3) Unidirectional.

29
Q
  1. Describe the directivity of an omnidirectional antenna.
A

It radiates energy equally well in all compass directions.

30
Q
  1. What is a drawback of using an omnidirectional antenna?
A

It is susceptible to interference from any direction.

31
Q

6–4. Antennas and Couplers

  1. Common air traffic control antennas
  2. Describe why the AT–197/GR antenna is considered a discone antenna.
A

The term “discone” describes the shape; the upper radiator forms a disc and the lower radiators are conical in shape.

32
Q
  1. What makes the AS
A

Its fiberglass radome enclosure.

33
Q
  1. What is the gain of the AS
A

4 dBi.

34
Q
  1. How much isolation do the AS
A

25 dB.

35
Q
  1. What does the term “multipole” mean?
A

Multiple antennas built into a single unit.

36
Q
  1. Why use an antenna coupler?

1. What is the purpose of an antenna coupler?

A

To match the equipment to the transmission line and antenna.

37
Q
  1. How many channels can one CU–547/GR support?
A

Up to four channels.

38
Q
  1. What frequency band is the CU–547/GR designed for?
A

UHF.

3D156 - Volume 1 (8 decks)

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