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Physics > 2-Signalling > Flashcards

2-Signalling Flashcards

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1
Q

What does a signal do?

A

A signal transfers information from one location to another.

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2
Q

What are the 2 ways signals can be converyed?

A

Through sound or light

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3
Q

What are digitised signals?

A

Signals of a string of binary digits from the sender to the reciever.

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4
Q

What is the number of bits required?

A

number of bits per character X number of characters per page X number of pages

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5
Q

What is 1 Byte?

A

8 Bits

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6
Q

What is an analogue signal?

A

Signals which vary from one value to the next without fixed values.

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7
Q

For most of the 20th century, what were most long distance communication systems examples of?

A

Analogue signals

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8
Q

What happens in an analogue telephone?

A

A sound vibration changes into matching oscillations of P.D.

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9
Q

What is the biggest problem with analogue signals?

A

The need for amplification as the signal becomes weaker

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10
Q

If the signal becomes distorted or ‘noisy’ what does the amplification do?

A

It boosts the signal and the noise.

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11
Q

What is the noise in relation to signals?

A

The random variation (the spiky parts)

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12
Q

What happens if you filter out the noise?

A

You lose a lot of detail in the signal.

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13
Q

What can transmit information quicker: digital signals or analogue signals?

A

Digital signals

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14
Q

What is sampling?

A

The process in which the signal is measured at small time intervals and turned into a digital string of binary numbers.

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15
Q

What is analogue to digital conversion?

A

When you convert varying analogue to a stream of numbers

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16
Q

What is the quantisisation error?

A

The difference between the signal value and the quantisation level.

17
Q

What is the resolution of a sample?

A

The smallest change in P.D that can be determined.

18
Q

What is the equation for resolution?

A

P.D range of signal / number of quantisation levels

19
Q

How do you calculate the number of quantisation levels possible?

A

2 to the power of the number of bits

20
Q

What is the resolution of a sample measured in?

A

Volts

21
Q

What does increasing the number of quantisation levels do?

A

It increases the demands on data storage and transmission.

22
Q

What is the equation for the maximum useful number of levels?

A

Total noisy signal variation / noise variation

b=log2( Vtotal/Vnoise )

23
Q

When working out the maximum number of useful number levels, do you round up or down?

A

You round up

24
Q

What is a frame rate?

A

The time interval between each frame

25
Q

What is the problem of not taking enough samples per second?

A

The signal will not be fully accurate

26
Q

What is the sampling rate?

A

The number of samples taken each second

27
Q

For a varying signal, what does the sampling rate have to be?

A

Sampling than the time interval between important changes in the signal.

28
Q

What happens if the sampling rate is too small?

A

The signal will lose detail

29
Q

What does the minimum sampling rate have to be?

A

Greater than 2 X the highest frequency component

30
Q

To ensure that the original signal can be met, what does the frequency have to be below?

A

A certain maximum

31
Q

What happens if the signal contains frequencies above a certain maximum?

A

The signal will not be constructed accurately

32
Q

What are aliases?

A

Lower frequecy signals which are not present in the original signal.

33
Q

As the human ear cannot detect sound above frequencies of 20kHz, what does the sampling frequency of music have to be?

A

Greater than 40kHz

34
Q

What is bit rate measured in?

A

Bit/second or Hz

35
Q

How do you calculate the bit rate?

A

Samples per second X bits per sample

36
Q

How do you calculate the duration of a signal?

A

Number of bits in signal / Bit rate

37
Q

As digital signals are numbers, what can happen to them?

A

They can be changed or scrambled

38
Q

Why is there no point using a voltage resolution better than the noise resolution of the signal?

A

You end up digitising noise

39
Q

Why is the number of bits b to use when digitising a signal is given by 2b = Signal / Noise ratio?

A

There is no point using a voltage resolution better than the noise variation of the signal, as you just end up digitising noise, thus we can write:
Noise variation = Voltage resolution
So Voltage resolution = Signal variation / 2b where b is the number of ADC bits
So Noise variation = Signal variation / 2b , which rearranges to give Signal variation / Noise variation = 2b

Physics (22 decks)

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