2-Signalling

Question 1

What does a signal do?

Answer 1

A signal transfers information from one location to another.

Question 2

What are the 2 ways signals can be converyed?

Answer 2

Through sound or light

Question 3

What are digitised signals?

Answer 3

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

Question 4

What is the number of bits required?

Answer 4

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

Question 5

What is 1 Byte?

Answer 5

8 Bits

Question 6

What is an analogue signal?

Answer 6

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

Question 7

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

Answer 7

Analogue signals

Question 8

What happens in an analogue telephone?

Answer 8

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

Question 9

What is the biggest problem with analogue signals?

Answer 9

The need for amplification as the signal becomes weaker

Question 10

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

Answer 10

It boosts the signal and the noise.

Question 11

What is the noise in relation to signals?

Answer 11

The random variation (the spiky parts)

Question 12

What happens if you filter out the noise?

Answer 12

You lose a lot of detail in the signal.

Question 13

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

Answer 13

Digital signals

Question 14

What is sampling?

Answer 14

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

Question 15

What is analogue to digital conversion?

Answer 15

When you convert varying analogue to a stream of numbers

Question 16

What is the quantisisation error?

Answer 16

The difference between the signal value and the quantisation level.

Question 17

What is the resolution of a sample?

Answer 17

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

Question 18

What is the equation for resolution?

Answer 18

P.D range of signal / number of quantisation levels

Question 19

How do you calculate the number of quantisation levels possible?

Answer 19

2 to the power of the number of bits

Question 20

What is the resolution of a sample measured in?

Answer 20

Volts

Question 21

What does increasing the number of quantisation levels do?

Answer 21

It increases the demands on data storage and transmission.

Question 22

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

Answer 22

Total noisy signal variation / noise variation

b=log2( Vtotal/Vnoise )

Question 23

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

Answer 23

You round up

Question 24

What is a frame rate?

Answer 24

The time interval between each frame

Question 25

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

Answer 25

The signal will not be fully accurate

Question 26

What is the sampling rate?

Answer 26

The number of samples taken each second

Question 27

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

Answer 27

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

Question 28

What happens if the sampling rate is too small?

Answer 28

The signal will lose detail

Question 29

What does the minimum sampling rate have to be?

Answer 29

Greater than 2 X the highest frequency component

Question 30

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

Answer 30

A certain maximum

Question 31

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

Answer 31

The signal will not be constructed accurately

Question 32

What are aliases?

Answer 32

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

Question 33

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

Answer 33

Greater than 40kHz

Question 34

What is bit rate measured in?

Answer 34

Bit/second or Hz

Question 35

How do you calculate the bit rate?

Answer 35

Samples per second X bits per sample

Question 36

How do you calculate the duration of a signal?

Answer 36

Number of bits in signal / Bit rate

Question 37

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

Answer 37

They can be changed or scrambled

Question 38

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

Answer 38

You end up digitising noise

Question 39

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

Answer 39

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