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ATAV 502: Comm Systems > Final Exam Review > Flashcards

Final Exam Review Flashcards

1
Q

What are the 3 types of microphones?

A

Electret
Dynamic
Carbon

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2
Q

Which of the microphones require an amplifier and why?

A

Electret and Dynamic

They only produce mV outputs that need to be amplified to match carbon mics

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3
Q

How does the electret microphone work?

A

sound = diaphragm vibration = distance btwn diaphragm and plate = electric signals
capacitance change

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4
Q

How does the dynamic microphone work?

A

A diaphragm moves a magnet/coil which creates a current

Electromagnetic effects

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5
Q

How does the carbon microphone work?

A

sound = carbon compressed by diaphragm = resistance change = current flow

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6
Q

What are the 3 parts of a jack?

A

Tip, Ring, Ground/Barrel

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7
Q

Which part of the jack is the PTT and what does it do?

A

The tip

When PTT is activated, tip is grounded which then we go from Rx to Tx

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8
Q

Which part of the jack is the audio?

A

The Ring which has a DCV supplied from radio

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9
Q

Which part of the jack is common to the PTT and audio?

A

The ground

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10
Q

Which mics require a bias voltage to operate and where does the voltage come from?

A

All mics require a bias voltage, they come from the radio itself

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11
Q

Aircraft microphones require a bias voltage of?

A

9V

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12
Q

Microphone impedance is what?

A

150ohms AC

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13
Q

Typical output voltage of microphones are what?

A

1Vrms

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14
Q

Headphone output impedance is?

A

500-600ohms

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15
Q

Speaker impedance is?

A

3.2 or 8 ohms

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16
Q

For power conversions what are the decibels?

A

3dB(2x) and 10dB(10x)

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17
Q

For voltage conversions what are the decibels?

A

6dB(2x) and 20dB(10x)

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18
Q

What is the reference level for dBm units?

A

1mW

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19
Q

What is the reference level for dBw?

A

1W

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20
Q

If an amplifier has a gain of 26dB and input voltage is 1mV what is the output voltage?

A

20mV

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21
Q

A transmitter has 3 stages with gains of 13dB, 20dB, and 3dB (total 36dB) if 2mW is input power what is the output power?

A

8W

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22
Q

If a signal generator attenuator is set to minus 20dBm what output power is sent?

A

0.01mW

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23
Q

Ground stations are identified during radios communications by?

A

Airport name and station type, ie Toronto tower.

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24
Q

What is the spoken word for distress?

A

Mayday

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25
Q

What is the spoken word for urgency?

A

Pan Pan

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26
Q

According to the radiotelephone operators guide Coordinated Universal time (UTC) is used to avoid confusion between different time zones. What is the accepted abbreviation for UTC?

A

Zulu time

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27
Q

What is the max output power for your radio license good for?

A

250W ERP

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28
Q

Who can get a radio license?

A

Anyone as long as they don’t have a disability that prevents them from operating a radio

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29
Q

What is the message format?

A

Who you are talking

then: this is
then: your call sign’\
then: your message
then: OVER

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30
Q

The time 4:45am is expressed as?

A

0445

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31
Q

The time 6:37pm is expressed as?

A

1837

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32
Q

A “.” is said as what?

A

Decimal

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33
Q

The word “HEAVY” is used to describe what?

A

An aircraft weighing more than 300,000lbs

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34
Q

If you need someone to repeat the message what do you say?

A

SAY AGAIN

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35
Q

How long should signal/radio checks last?

A

10s

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36
Q

On a signal/radio check, when someone responds “5 by 5” what does the first and second numbers mean?

A

the first number is the READABILITY

the second number is the STRENGTH

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37
Q

When carrying out a VSWR test a forward power of 100W and reverse power of 1 watt is measured, what is the VSWR?

A

1.2:1

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38
Q

When carrying out a VSWR test a forward power of 100W and reverse power of 10 watt is measured, what is the VSWR?

A

2:1

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39
Q

What value of VSWR is the acceptable limit?

A

2:1

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40
Q

If the antenna transmission line (co-ax) is open circuit what VSWR or SWR would be measured?

A

5:1

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41
Q

When testing a transmission line with a TDR, what indication would a short in the line show as?

A

Downward deflection on trace

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42
Q

When testing a transmission line with a TDR, what indication would an open in the line show as?

A

Upward deflection on trace

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43
Q

When testing VSWR, if you put the Wattmeter at the ANT and it passes at the ANT but fails at the Comm, what is faulty?

A

Transmission Line/ Co-ax is faulty

44
Q

When testing VSWR, if it fails at both the ANT and the Comm, what is faulty?

A

The Antenna

45
Q

What are the frequencies that you test the VSWR on?

A

118MHz, 126.5MHz, 136.975Mhz

46
Q

If the antenna transmission line (co-ax) is a perfect circuit what VSWR or SWR would be measured?

47
Q

When testing a 121.5MHz ELT what time restriction must be observed?

A

First 5min after the hour

48
Q

ELTs have an arrow on the case. For proper installation where should the arrow point?

A

Towards the direction of flight / front of aircraft

49
Q

What advantage does the 406MHz ELT have over 121.5MHz ELT?

A

Gives more accurate position coordinates

50
Q

ELT non-rechargeable batteries must be replaced after:

A

activation Unknown duration
on or before batt. replacement
after ELT used in emergency
when sum of all tx exceeds 1hr

51
Q

Replacement of ELT batteries should be done?

A

When testing shows insufficient charge

52
Q

When can you transmit using the 406.025MHz ELT?

A

Not allowed at any time

53
Q

What are the restrictions on performing a self test tx on a 406MHz ELT and how many bursts are we looking for?

A

No restrictions, 1 burst

54
Q

ELT rechargeable batteries must be recharged after:

A 
activation Unknown duration
after ELT used in emergency
when sum of all tx exceeds 1hr
time intervals specified by manuf.
Immediately before ELT installed on airc.
55
Q

What is the transmits power output used on the 121.5MHz ELT?

56
Q

What is the transmits power output used on the 406MHz ELT?

57
Q

An ELT has to be inspected every?

58
Q

What is the modulation used on the 121.5MHz ELT?

59
Q

What is the modulation used on the 406MHz ELT?

A

Phase/DPSK

60
Q

What is the modulation type used on the 121.5MHz ELT?

A

Swept tone

61
Q

What is the modulation type used on the 406MHz ELT?

62
Q

The 406 ELT transmits for ______ every _______

A

0.5s every 50s

63
Q

The 121.5MHz ELT transmits:

A

Continuously/Repetitively

64
Q

The 406 MHz ELT output consists of a ______ but pulse train

A

112(short) and 144(long)

65
Q

The 121.5MHz ELT is modulated by a distinct down-sweeping audio tone varying between _______ at a rate of ______

A

1600-300Hz

3Hz

66
Q

What frequency spacing is used for the HF comm?

67
Q

What is the purpose of the antenna coupler in an HF installation?

A

To compensate for incorrect antenna length

68
Q

What is the purpose of the lightning arrester?

A

Protect the receiver

69
Q

The clarifier has a frequency range of about?

70
Q

Civilian aircraft are restricted to use the ______ side band on HF transmissions?

A

Upper Sideband

71
Q

What is the typical output power of an HF transmission?

A

150W PEP (100-400W PEP)

72
Q

What is the purpose of the clarifier?

A

Changes the frequency of the carrier oscillator during Rx only

73
Q

Where is clarifier located?

A

In the BFO

74
Q

If the mic is keyed and we don’t speak but there is still a power output what is happening?

A

Faulty, diode could be broken keeping it unbalanced

75
Q

HF audio response/bandwidth is?

A

350Hz to 2500Hz

76
Q

At 2MHz how much Hz does the clarifier supply?

What about for 30MHz?

A

+/- 17MHz

+/- 250Hz

77
Q

On HF, how do you perform a sensitivity test in SSB?

A

Carrier only (no modulation) at 1kHz above the Rx selected freq.

78
Q

VHF frequency range is?

A

118MHz to 136.975MHz

79
Q

VHF range is based on?

80
Q

VHF bandwidth is what?

81
Q

VHF channel spacing is what?

A

25kHz or 8.33kHz

82
Q

What is the purpose of the limiters on VHF?

A

prevent modulation from going over 90%

83
Q

Typical VHF comm power output?

84
Q

What is the VHF comm duty cycle?

A

4min off, 1min on

85
Q

What is the purpose of the AGC?

A

Keep the volume approximately constant during signal strength variations at its input (maint. level within 3dB)

86
Q

How do you test the AGC?

A

Done after the sensitivity test, 1kHz 30% mod, adjust generator output from 10uV to 20000uV, make sure no 3dB change

87
Q

What controls the gain of the IF so that the proper voltage always comes out of the Detector?

88
Q

What is squelch?

A

a unique circuit for comms, it keeps the audio nice and quiet unless we are receiving a signal

89
Q

What do we use to monitor backup/carrier squelch?

90
Q

Squelch operates at how many volts?

A

2uV (1kHz at 30%mod)

91
Q

AGC operates at how many volts?

A

20uV (8kHz at 85%mod)

92
Q

What does ACARS stand for?

A

Aircraft Communications Addressing and Reporting System

93
Q

What is the last way to transmit ACARS if everything else has failed?

94
Q

ACARS transmits how man bits per second?

95
Q

What is the ACARS message format?

A

Preamble, Text, Block check

96
Q

Why is a Low Pass Filter connected between the output of a transmitter and the antenna?

A

To reduce the possibility of transmitting harmonics

97
Q

How many audio tones for SELCAL?

A

4 tones (2 tones sent at the same time)

98
Q

How long are each bursts?

A

1s with a 0.2s pause then the other 1s

99
Q

Each SELCAL pulse has a carrier that is modulated by how many %?

100
Q

How is the SELCAL decoder reset?

A

Reset by the PTT on transceiver

101
Q

How does the pilot know what his SELCAL code is?

A

A placard on the windshield above the cowl

102
Q

What is the proper sequence of a SELCAL code?

A

Cannot have a letter later in the alphabet come before earlier ones

103
Q

What is the frequency of a SATCOM air to satellite transmission?

A

1500/1600MHz

104
Q

What is the frequency of a SATCOM satellite to ground transmission?

A

4000/6000MHz

105
Q

Where in the SATCOM system would you find an electro-mechanical Beam steering unit?

A

In a HIGH gain antenna system

106
Q

Where in the SATCOM system would you find a conformal beam steering unit?

A

In a LOW gain antenna system

107
Q

Operating the test switch or button on a VHF communication radio to verify serviceability actually tests:

A

The receiver from the IF amp to audio amp and the PSU

ATAV 502: Comm Systems (5 decks)

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