Triple Waves

Question 1

What is an analogue signal?

Answer 1

• In an analogue signal the information is converted into electrical voltage currents that vary continuously
• An analogue signal follows the actual pattern of the original information
• Can take any value within a certain range
• The amplitude and frequency of an analogue signal can vary continuously

Question 2

What is a digital signal?

Answer 2

-The information is converted into binary code
-Uses just two digits 0 and 1
-These numbers are then converted into a series of electrical pulses that are sent down the telephone
-Can only take two values either on/off or 1/0
E.G you can send data along optical fibres as short pulses of light

Question 3

What are the advantages of digital signals over analogue signals?

Answer 3

1. All signals become weaker during transmission and need to be amplified or regenerated:
   - Digital signals: when regenerated create a clean and accurate copy of the original signal
   - Analogue signals: when amplified any accompanying noise is also amplified and as a result the level of noise may “drown out” the original signal or introduce errors in the information being carried
2. Because of this is it is easier to transmit multiple signals at the same time with just one cable or EM wave (a process called multiplexing) if the signal is digital
3. If analogue waves are of similar frequency it can cause interference when the signal looses quality.
4. With digital signals it is much easier to tell them apart, so you can transmit more information along the same channel
   - Therefore using digital signals, more programmes ca be broadcast over the same frequencies

Question 4

How come digital signals can carry more information?

Answer 4

1. Quantisation is the process of rounding multiple values to a smaller set
2. By doing this you can pack in more information into the same amount of space
3. Because digital signals only have two values, quantisation does not loose much information
4. However with an analogue signal a lot of information is lost when a continuous range is rounded off

Question 5

What is interference?

Answer 5

• When two or more waves of a similar frequency meet, they can create one combined signal with a new amplitude
• You get it when two radio stations transmit on similar frequencies

Question 6

How can an oscilloscope and microphone display sound waves?

Answer 6

1. A sound wave receiver, such as a microphone can pick up sound waves travelling through the air
2. To display these sound waves, and measure their properties, you can plug the microphone into an oscilloscope
3. The microphone coverts the sounds waves to electrical signals
4. An oscilloscope is a device which can display the microphone signal as a trace on a screen
5. The appearance of the wave on the screen tells you whether the sound is loud or quiet, and high or low-pitched
6. You can even take detailed measurement to calculate the frequency of the sound by adjusting the settings of the display

Question 7

How does loudness change with amplitude?

Answer 7

1. The greater the amplitude of a wave or vibration, the more energy it carries
2. In sound this means it will be louder
3. Louder sound waves will also have a trace with a larger amplitude on an oscilloscope

Question 8

How does the frequency affect the pitch?

Answer 8

1. You can compare the frequency of waves on an oscilloscope, as the more complete cycles displayed on the screen, the higher the frequency, as long as the waves are being compared on the same scale
2. If the source of sound vibrates with a high frequency the sound is high-pitched
3. If the source of sound vibrates with a low frequency the sound is low pitched

Question 9

How do you measure frequency of a sound wave on an oscilloscope?

Answer 9

1. The horizontal axis on the display is time. The time between each division on the scale can be adjusted to get a clear readable trace
2. Adjust the time division setting until the display shows at least 1 complete cycle
3. Read off the period - the time taken for one complete cycle, so if one cycle is completed in 20 divisions and each division is 0.0001 seconds (from the setting), then the period is 0.0002 seconds
4. Frequency = 1 / period so 5kHz