64ET1405 Elec

1
64ET1405 Elec Net Principles

• Topic One Lab Session
• Testing your knowledge of the Comms SystemsLab
  Session
• Updated 10 July 2006
• George South

2
64ET1405 E Net Principles

• Topic One Lab Session
• Link to AM http//cnyack.homestead.com/files/modul
  ation/modam.htm
• Link to FM
• http//cnyack.homestead.com/files/modulation/modfm
  .htm

3
1. Typical results from the audio perception
tests indicate

• All people have very similar hearing
• Most people can hear frequencies up to about 12
  KHz
• Few people can hear frequencies above 4 KHz
• Most people can hear sounds above 18 KHz

4
2. Typical results from the audio perception
tests indicate

• Most people can hear sounds above 200 Hz
• Frequencies below 100 Hz are an important part of
  speech
• Most people can hear frequencies below 40 Hz
• Small speakers are good at reproducing low
  frequencies

5
3. Concerning speakers and head phones

• Simple speakers can reproduce a wide range of
  frequencies
• Speakers produce the same audio output at all
  frequencies
• For the same price you get much better quality
  from headphones
• Small speakers are good at reproducing low
  frequencies

6
4. The term AC when referring to an audio
waveform means that

• The signal contains positive and negative
  components
• The signal must be a perfect tone (sine wave)
• The signal is a square wave
• The signal is not audible

7
5. A 10 Watt speaker

• Delivers 10 Watts audio power to the listener
• Is large and expensive
• Is adequate for simple domestic and commercial
  audio
• Usually uses electrostatic technology

8
6. A budget 10 Watt speaker driven by a 10 Watt
amplifier will sound

• Quite loud
• Very loud
• Quiet
• Very quiet

9
7. An 8 Ohm speaker is delivering a genuine 8
Watts

• The current is 1 Amp RMS (or AC)
• The current is 8 Amps RMS
• No current is needed to drive 8 Ohm speakers
• The current is 64 Amps DC
• P I times I Times R so 8 I times I times 8

10
8. Which of the following is true

• CDs are sampled at 96 KHz
• CDs use 8-bit resolution
• If a CD is transferred to DVD technology it will
  sound better
• CDs audio tracks are not compressed

11
9. Which of the following is true

• The human ear can resolve sound to about 64000
  levels (16-bit)
• The human ear can resolve sound only to 256
  levels (8-bit)
• MP3 files are much bigger than equivalent WAV
  files
• Apple ipods use WAV files

12
10. Which of the following is true

• CDs store music data as MP3 files
• CDs store music data as WAV files
• CDs store music data in a compressed format
• CDs contain analogue and digital data

13
11. Radio stations use modulation why not
transmit raw audio ?

• All stations would use the same frequencies
  leading to chaos
• Radio transmissions dont work at audio
  frequencies
• The aerials are too small at audio frequencies
• Transmitting audio frequency radio waves would
  deafen people near the transmitter

14
12. Comparing AM and FM - Which gives the better
quality ?

• AM because it is simpler
• AM because it provides redundant information
• FM because it is immune to noise
• FM because the carrier frequency doesnt change

15
13. Comparing AM and FM

• FM was used for early broadcasts
• AM technology is ideal for use with computers
  (only 1s and 0s)
• AM is the simpler form of modulation
• FM is used by modern mobile phones

16
14. Streaming Technology

• Is used by terrestrial TV
• Is used by internet radio
• Sends audio or video is very large blocks
• Is the primary technology for IE6

17
15. The Formula for Power is

• P I times V
• P V divided by R
• P I times R
• P R times I

18
16. The most recent innovation in radio is DAB,
this stands for

• Digital AM Broadcasting
• Digital Audio Broadcasting
• Dynamic Audio Broadcasting
• Direct Audio Broadcasting

19
17. Which of the following is an AM radio
station

• BBC Radio 1(97.6 - 99.8 MHz)
• BBC Radio 2(88-90 MHz)
• BBC Radio 3(90.2 - 92.4MHz)
• BBC Radio 4(198 KHz)

20
18. A 3G mobile phone uses which frequency range ?

• 2.1 GHz
• 90 MHz
• 900 MHz
• 1800 MHz

21
19. Mobile systems are called GSM which stands
for

• Global System for Mobile Comms
• GHz Standard Mobile Comms
• Global Standard for Mobile Comms
• GHz System for Mobile Comms

22
20. A 2G mobile phone

• Is analogue
• Cannot handle text messages
• Cannot provide fast internet access
• Is digital

23

• End of test
• Please report any errors to George South