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TO3 > Amplitude Modulation (AM) > Flashcards

Amplitude Modulation (AM) Flashcards

1
Q

What is the need for modulation

A

Voice is not electromagnetic waves therefore it’s limited over a distance to which it can be propogated.

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2
Q

What is the definition for modulation?

A

The process whereby information is superimposed onto a radio frequency (RF) carrier wave.

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3
Q

Three main types of modulation?

A

Amplitude frequency and phase

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4
Q

What is a modulating wave?

A

The waveform of the original intelligence. My voice into a radio station is the modulating wave.

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5
Q

What is a carrier wave?

A

The waveform used to carry the modulating wave which gains the distance it needs.

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6
Q

What is another word for radio frequency?

A

Carrier wave.

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7
Q

What is the modulated wave ?

A

The waveform created by encoding the modulating wave onto the carrier wave which is then transmitted to the receiver.

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8
Q

What is the definition of AM?

A

The amplitude of the modulated wave is varied in accordance with the amplitude of the modulating wave.

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9
Q

What is demodulation?

A

The process of intercepting a signal to gain the original intelligence.

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10
Q

If the amplitude of the transmission stays the same it is said to have what?

A

A constant envelope.

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11
Q

If the amplitude of the transmission varies it is said to have a what ?

A

A periodic envelope.

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12
Q

How do you work out transmitter bandwidth ?

A

2 x the modulating frequency.

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13
Q

What is the lower side band a mirror image of ?

A

The upper side band and vice versa.

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14
Q

What is transmission bandwidth?

A

The bandwidth of a transmission is difference in Hertz between the lowest and highest frequency components of the complex waveform.

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15
Q

How is a constant envelope created ?

A

When the amplitude of the wave stays the same over a period of time

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16
Q

What is a periodic envelope?

A

When the amplitude varies in a repetitive manner.

17
Q

What are the upper and lower side bands replicas of ?

A

The modulating wave.the upper and lower halves mimic the modulating wave.

18
Q

What makes up a modulated wave ?

A

The radio frequency and the modulating wave.

19
Q

What is depth of modulation?

A

How much the modulating wave affects the carrier wave, the resultant waveform and frequency spectrum.

20
Q

How do you work out depth of the modulation ?

A

Peak audio frequency
———————- x100=depth
Peak radio frequency

21
Q

Which always has to be higher power, AF voltage or RF voltage?

A

RF voltage should be higher then AF

22
Q

What is depth of modulation measured in ?

A

Percentage %

23
Q

What is the definition for Double side and?

A

Both bands of frequencies produced by the process of modulation are transmitted equally.

24
Q

Where is the intelligence within a modulated wave ?

A

Within the modulating wave.

25
Q

3 types of DSB carriers?

A

Reduced, suppressed and full carriers.

26
Q

What does it mean when a band of frequencies is said to be erect?

A

When the highest radio frequency refers to the highest audio frequency and the lowest radio frequency corresponds to the lowest audio frequency.

27
Q

A band of frequencies is said to be inverted when what ?

A

When the highest radio frequency refers to the lowest audio frequency and the lowest audio frequency corresponds to the highest audio frequency.

28
Q

3 Disadvantages of double side band ?

A

Waste of transmitter power- the carrier contains no intelligence but two thirds of the total power

Excessive bandwidth- both side bands together create a bigger bandwidth as they carry the same intelligence

Prone to selective fading- may fade side bands. Resulting in one frequency rubbing into the other creating distortion.

29
Q

What can we do to counter DSB disadvantages?

A

Use single side band

30
Q

What is the definition of a single side band ?

A

Either the upper or lower side band is transmitted.

31
Q

What is a single side band ?

A

When the modulated signal has been made it can be completely or partially suppressed before transmission. Resulting in one side band being attenuated or filtered only transmitting one side band.

32
Q

What does SSBSC stand for ?

A

Single side band suppressed carrier

33
Q

Re insert carr

A

Re insert carrier frequency
Equipment requires stability
Expensive
Complex

TO3 (10 decks)

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