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Comm 01 - Propagation Paths & Basic Radio Systems Flashcards

1
Q

What are the different propagation paths?

A

Ground wave
Tropospheric Wave Ducting
Sky wave

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2
Q

What wave has a portion of its radiated energy affected by the presence of the earth and its features?

A

Ground wave

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3
Q

What are the two ground wave components?

A

Surface and space wave

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4
Q

Describe the path of a surface wave.

A

Travels along the surface of the earth and tends to curve over the horizon due to refraction

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5
Q

Why are ground waves only useful in the Low and Very Low Frequency (VLF)?

A

Attenuation of the surface wave rapidly increases as the frequency increases.

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6
Q

What is the max range in the MF and low HF bands for a ground wave?

A

100 NM

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7
Q

What two components make up a space wave?

A

Direct wave and earth-reflected wave

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8
Q

What is a Space wave limited to?

A

LOS ranges

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9
Q

What is Tropospheric Wave Ducting?

A

Path taken by the radiation that undergoes refraction and reflection in the lower levels of the atmosphere

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10
Q

What causes the Tropospheric Wave Ducting to refract and reflect?

A

Abrupt changes in temperature and moisture

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11
Q

What is a Sky Wave?

A

Waves that travel upward then reflected back to the earth by the ionosphere.

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12
Q

What is the frequency range for sky propogation?

A

300KHz to 30 MHz

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13
Q

What frequency bands do Sky Waves occur in?

A

MF to HF

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14
Q

Which wave propogation gives the most reliable and distant comms?

A

Sky Waves

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15
Q

What is a communication system?

A

A system designed for the purpose of transmitting information rom one point to another.

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16
Q

A basic comm system is made up of three parts, what are they?

A

Transmitter, receiver and antennas

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17
Q

What two sections is a transmitter composed of?

A

A radio frequency and modulator section

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18
Q

What does the Oscillator Generator do?

A

Generates EM energy at the desired frequency, known at the carrier wave. (think a blank CD)

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19
Q

What does the Modulator do?

A

Desired intelligence is entered into the modulator by means of a microphone, keyboard etc…
Intelligence is then impressed on the carrier wave by the modulator.

20
Q

What are the different types of modulation?

21
Q

What does the Amplifier do in the transmitter?

A

It amplifies the modulated signal and sends it to the antenna for transmission.

22
Q

What components make up the receiver?

A

Antenna. selective circuit, detector and audio amplifiers

23
Q

What does the selective circuit do?

A

Provides selectivity by only allowing energy of a pre-tuned frequency to pass into the receiver.

24
Q

What does the detector do?

A

Detects and demodulates the the intelligence from the carrier wave (splits the wave in two so we can read the intelligence portion)

25
What do the audio amplifiers do? Why are they necessary?
Steps up the power and reproduces the intelligence signal for use. Without amplifiers, the signal would not have enough energy to be heard from the speaker.
26
What are the desirable receiver functions?
Intercept some of the RF energy from the transmitter Select the correct RF from a multitude of signals Detect and separate the intelligence from the carrier wave Reproduce the intelligence into some meaningful form
27
What are the Receiver Characteristics?
Frequency coverage Sensitivity Selectivity Fidelity
28
Describe the frequency receiver characteristic
It refers to the range of radio frequencies the receiver can handle Receivers cannot intercept all frequencies, they are optimized for specific frequency bands
29
Describe the sensitivity receiver characteristic
Refers to the ability of a receiver to intercept weak signals and extract the intelligence A highly sensitive receiver will work for both strong and weak signals
30
Describe the selectivity receiver characteristic
Ability of a receiver to intercept and extract intelligence from a desired signal and exclude all others.
31
Describe the fidelity receiver characteristic
Ability to reproduce the transmitted intelligence Not necessary for voice comms, it is for data link
32
What does an antenna do? What are its functions?
Antennas couple the radio system to free space A single antenna can both transmit and receive, but not at the same time
33
An antenna contains electrons that?
Oscillate at the desired frequency and send EM waves to be formed and radiated away from it
34
An antenna's oscillation contains what two type of components in it's field?
Electric (E) and magnetic (H)
35
What is an antenna's gain?
The measurement of an antenna's ability to radiate energy in a particular direction.
36
True or false Gain is a function of an antenna's size and shape
True
37
Describe polarization regarding an antenna's orientation.
It is the orientation of the E field of the wave with respect to the earth.
38
What determines the polarization of the the radio wave?
The orientation of the transmitting antenna.
39
If two antennas are not close in orientation, what is the theoretical power loss?
50 - 99%
40
Explain the receiving antenna behaviour.
EM waves from transmitting antenna excite or oscillate the electrons in the receiving antenna. An electric current is formed and conducted to the receiver.
41
Review Questions Describe Tropospheric Wave Ducting
Part of the radiation that undergoes refraction and reflection in the lower levels of the atmosphere. Provides extra range to LOS comms Unpredictable
42
Review Questions What three parts make up a basic radio comm system?
Transmitter, receiver and antenna
43
Review Questions What is the frequency produced by the RF section of a transmitter called?
Carrier wave
44
Review Questions What does the antenna system do?
Couples the radio to free space by radiating RF energy from the transmitter and capturing the RF energy by the receiver.
45
Review Questions What are the four characteristics of a receiver?
Frequency coverage Sensitivity Selectivity Fidelity

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