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Comme Theory > Book 2 > Flashcards

Book 2 Flashcards

1
Q

Types of Analogue Modulation

A
  • Amplitude modulation
  • Single side band
  • Frequency Modulation
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2
Q

What does the modulator do?

A

Changes the audio frequency signals to radio frequency signals

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3
Q

What is a Bandwidth?

A

The bandwidth is the difference in hertz between the highest frequency and the lowest frequency used by a signal.

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4
Q

What is Depth of Modulation?

A

Modulation depth is the ratio between the maximum carrier amplitude and the minimum amplitude.

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5
Q

What is the Depth of Modulation Formulae?

A

H-h/H+h x 100%

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6
Q

What is modulation depth?

A

A measure of how loud the audio signal is

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7
Q

What are the consequences of Over Modulation?

A
  • Audio signal output will be distorted
  • Additional side bands will be created leading to adjacent channels
  • Wasted power
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8
Q

What is the purpose of the Master Oscillator (MO)?

A

Generates the carrier signal at the required transmission frequency

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9
Q

What is the purpose of the Buffer Amplifier?

A

Protects the Master Osciallator for loading

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10
Q

What is the purpose of the AF Amplifier?

A

Provides sufficient audio power to give the required modulation depth.

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11
Q

What is the purpose of the Driver Amplifier?

A

To ensure the Power Amolifier stage receives a sufficiently large input signal voltage to enable maximum Power Amplifier output power to be produced.

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12
Q

What is the purpose of the Power Amplifier?

A

Amplifies the RF signal to provide sufficient RF power to the aerial to ensure the transmitted signal reaches the receiver.

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13
Q

What is the purpose of the Side Tone?

A

A sample of the transmitted signal from the aerial and converts it into an audio signal allowing the operator to hear their own voice.

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14
Q

What is the purpose of the Voice Operated again Adjustment Device (VOGAD)?

A

To ensure a reasonably constant modulation depth over a wide range of input amplitudes.

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15
Q

What are the four characteristics of an AM modulation receiver?

A
  • Sensitivity
  • Signal to Noise Ratio
  • Selectivity
  • Fidelity
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16
Q

What is Sensitivity?

A

The ability of a receiver to produce a good output from a weak input signal.

17
Q

What is Signal to Noise Ratio (SNR)?

A

The quality of the receiver output compared to the noise surrounding it.

18
Q

What is Selectivity?

A

The ability of the receiver to pick up unwanted signals and reject all others.

19
Q

What is Fidelity?

A

A receivers ability to reproduce an output which is an exact copy of the modulation input to the transmitter.

20
Q

What is a Resonant Frequency?

A

The ‘Resonant Frequency’ is the frequency that the circuit is designed to operate most effectively.

21
Q

What are the three common uses of Filters?

A
  • Frequency Modulation detection
  • Single Sideband generation
  • Double Sideband generation
22
Q

What is the purpose of the Local Oscillator?

A

Generates a signal that is different from the required signal by the intermediate Frequency (IF)

23
Q

What is the purpose of the Mixer?

A

Converts the selected channel frequency (RF) to the fixed intermediate frequency (IF).

24
Q

What are the Advantages of the RF Amplifier?

A
  • Prevents 2nd Channel interference
  • Prevents IF Breakthrough
  • Prevents Local Oscillator Radiation
  • Improves the receivers SNR
25
Q

What is Frequency Synthesis?

A

Through allowing the user to save a required signal, it allows for the quick selection between frequencies.

26
Q

What is the purpose of the IF Amplifier?

A
  • Provides the majority of the gain (1 million)
  • Prevent adjacent channel interference
  • Allows for Selectivity
27
Q

What is the purpose of the Audio Detector?

A

Changes the RF signals to AF signals

28
Q

What is the purpose of the AF Amplifier in a receiver?

A

Produces sufficient power to drive the loudspeaker or headset

29
Q

What is the purpose of the Squelch Circuit?

A

Prevents operator fatigue by disconnecting the audio output under no signal conditions

30
Q

What is the purpose of the Automation Gain Control?

A

To maintain a reasonably constant receiver output level for a wide range of signal strengths at the aerial.

31
Q

What is the purpose of a Simple AGC?

A

To maintain contestant output by automatically reducing the overall gain of the receiver for increased signal input levels.

32
Q

What is the purpose of the Delayed AGC?

A

No AGC is applied and the receiver gain is kept at maximum gain until the receiver input achieves a pre-set level.

33
Q

What does Frequency Synthesis allow for?

A
  • Fast Tuning
  • 20,000 channels
  • Reducing head down
  • Digital Frequency control
  • Frequency hopping
34
Q

What is the purpose of the Voice Controlled Oscillator (VCO)?

A

Takes the part of the master oscillator for the transmitter and the local oscillator for the receiver

35
Q

What is the purpose of the Tone Oscillator?

A

The cockpit headset is replaced by a 1kHz audio signal.

36
Q

What is the purpose of the Guard Receiver?

A

Emergency frequency that is permanently tuned to 243MHz

Comme Theory (5 decks)

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