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Comms > Comm 01 - Propagation Paths & Basic Radio Systems > Flashcards

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?

A

AM and FM

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
Q

What do the audio amplifiers do? Why are they necessary?

A

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
Q

What are the desirable receiver functions?

A

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
Q

What are the Receiver Characteristics?

A

Frequency coverage
Sensitivity
Selectivity
Fidelity

28
Q

Describe the frequency receiver characteristic

A

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
Q

Describe the sensitivity receiver characteristic

A

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
Q

Describe the selectivity receiver characteristic

A

Ability of a receiver to intercept and extract intelligence from a desired signal and exclude all others.

31
Q

Describe the fidelity receiver characteristic

A

Ability to reproduce the transmitted intelligence

Not necessary for voice comms, it is for data link

32
Q

What does an antenna do? What are its functions?

A

Antennas couple the radio system to free space

A single antenna can both transmit and receive, but not at the same time

33
Q

An antenna contains electrons that?

A

Oscillate at the desired frequency and send EM waves to be formed and radiated away from it

34
Q

An antenna’s oscillation contains what two type of components in it’s field?

A

Electric (E) and magnetic (H)

35
Q

What is an antenna’s gain?

A

The measurement of an antenna’s ability to radiate energy in a particular direction.

36
Q

True or false

Gain is a function of an antenna’s size and shape

A

True

37
Q

Describe polarization regarding an antenna’s orientation.

A

It is the orientation of the E field of the wave with respect to the earth.

38
Q

What determines the polarization of the the radio wave?

A

The orientation of the transmitting antenna.

39
Q

If two antennas are not close in orientation, what is the theoretical power loss?

A

50 - 99%

40
Q

Explain the receiving antenna behaviour.

A

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
Q

Review Questions

Describe Tropospheric Wave Ducting

A

Part of the radiation that undergoes refraction and reflection in the lower levels of the atmosphere.
Provides extra range to LOS comms
Unpredictable

42
Q

Review Questions

What three parts make up a basic radio comm system?

A

Transmitter, receiver and antenna

43
Q

Review Questions

What is the frequency produced by the RF section of a transmitter called?

A

Carrier wave

44
Q

Review Questions

What does the antenna system do?

A

Couples the radio to free space by radiating RF energy from the transmitter and capturing the RF energy by the receiver.

45
Q

Review Questions

What are the four characteristics of a receiver?

A

Frequency coverage
Sensitivity
Selectivity
Fidelity

Comms (9 decks)

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