2: Signalling Flashcards
What are digital signals represented by?
Binary numbers
Are Analogue signals limited in the values they can take?
No. They also vary continuously
When you transmit an electronic signal will pick up noise. From what does it pick up noise?
Electrical disturbances or other signals
Why is it easier to reconstruct the original signal from the noisy signal with digital signals? Why do it?
The number of values, a digital signal can take is limited
You need to get an accurate representation of what was sent
Can Analogue signals be digitised?
Yes
How do you digitise a signal?
You take the value of the signal at regular time intervals then find the nearest digital value
Each digital value is represented by a binary number so you can convert the analogue values to binary numbers
The digital signal you end up with won’t be exactly the same as the analogue signal
What 2 factors affect how well a digitised signal matches the original?
The difference between the possible digital values (resolution) and the time from one sample to the next (sampling rate)
What happens if a signal is digitised using only a few, widely spaced digital values?
It’s likely that a lot of the analogue values sampled will be far from the nearest digital value.
What is the advantage of a higher resolution? And what does a higher resolution mean?
Higher res: more possible digital values
Ad: The more closely the digitised signal will match the original
What is resolution determined by?
The number of bits in the binary numbers representing the digital values - the greater the no. of bits, the greater the resolution
What is the advantage of using a lower resolution?
Lower rate of transmission can be used to send the information
What are the advantages of digital over analogue signals (5)?
1) Digital signals can often be sent, received and reproduced more easily than analogue signals because they can only take a limited number of values
2) Digital files can be compressed to reduce their size, and manipulated easily for artistic effect
3) Noise is more of a problem for analogue signals than digital
4) A digital signal can be used to represent different kinds of information in the same way
5) Computers can be used to easily process digital signals as computers are also digital devices
What are the disadvantages of digital over analogue signals (3)?
1) Digital signals can never reproduce analogue signals exactly - some information will always be lost
2) Because digital signals can be copied more easily, digital information (films etc.) can be reproduced illegally unlimited times
3) Confidential information, such as personal data and photos, may be stolen or copied without the owner’s knowledge or consent, more easily by hackers, infected networks or malicious websites
Most signals are made up of several [ ] all with different [ ]
waves
frequencies
When you have a signal made up of different waves, how do you work out the amplitude at a given point?
The amplitude of the final signal is the sum of the amplitudes of the individual waves at each point in time
