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ENGINEERING, TE 2018 HSC 13 MC

Which statement best describes modulation?

  1. The addition of information to a carrier wave.
  2. The attenuation of information in a carrier wave.
  3. The removal of quantised information from a carrier wave.
  4. The filtering of unnecessary information from a carrier wave.
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`A`

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  • Modulation converts data to radio waves by adding information to a carrier signal/wave (ie Amplitude Modulation or Frequency Modulation)

`=>A`

Mean mark 57%.

ENGINEERING, TE 2019 HSC 26b

A simple circuit diagram of the AM radio receiver is shown.
 

  1. Complete the table giving the function of each of the circuit components listed.   (5 marks)
     

  1. Complete the table by drawing the waveform at positions B and C.   (2 marks)
     

  1. This AM radio receiver produced a demodulated electrical signal with a small current. The speakers in the earphones converted this signal into sound.
  2. Explain why the speakers in the earphones required a high impedance (resistance) in order to produce sound of sufficient volume to be heard.   (2 marks)
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“

Show Worked Solution

i.  


♦ Mean mark (i) 47%.

ii.  


♦♦♦ Mean mark (ii) 22%.

iii.  An external power source is not used to power this radio.

  • The signal picked up by the aerial powers the speakers.
  • If the impedance (resistance) is high an audible signal can be generated by the speaker at a low current.
  • Because the earphone impedance is high, the sensitivity of the coil improves, resulting in a more accurately tuned signal.
  • The sound would be inaudible if the impedance is low, as the power to the earpiece would also be low.

♦♦♦ Mean mark (iii) 15%.

ENGINEERING, PPT 2019 HSC 26a

The photograph shows an AM radio coupled to a pedal-powered generator. This radio allowed communication in remote areas of Australia during the 1920s.
 

Explain how the mechanical energy from pedalling was converted into electrical energy in the generator to power the AM radio.   (3 marks)

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  • A generator consists of a magnet surrounded by a coil of wire.
  • Pedalling causes the magnet to spin and electricity is produced within the coil through magnetic induction.
  • The radio transceiver is powered by the generated electrical energy.
  • As the generator’s speed increases so does the voltage supplied.
Show Worked Solution
  • A generator consists of a magnet surrounded by a coil of wire.
  • Pedalling causes the magnet to spin and electricity is produced within the coil through magnetic induction.
  • The radio transceiver is powered by the generated electrical energy.
  • As the generator’s speed increases so does the voltage supplied.

ENGINEERING, TE 2019 HSC 14 MC

Which row of the table correctly identifies key features of analogue and digital signals used in the transmission of television in Australia?
 

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`A`

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By Elimination:

  • VOIP is used to transmit audio, not video (not `C` or `D`)
  • FM signals are better for transmitting audio as they offer a higher fidelity than AM, creating a more accurate reproduction of the original sound (not `B`)

`=>A`


♦ Mean mark 42%.

ENGINEERING, TE 2020 HSC 26c

Discuss methods for increasing the signal strength of a receiving antenna.   (3 marks)

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  • Amplification: Amplifies the sound, however this could include unwanted background noise.
  • Antenna tuning: The antenna can be tuned to the frequency of interest. This can be done by adjusting the length of the antenna, however this may not be practical in some scenarios.
  • Directional antenna can focus the signal to increase strength however misalignment could result in losing the signal entirely.
Show Worked Solution
  • Amplification: Amplifies the sound, however this could include unwanted background noise.
  • Antenna tuning: The antenna can be tuned to the frequency of interest. This can be done by adjusting the length of the antenna, however this may not be practical in some scenarios.
  • Directional antenna can focus the signal to increase strength however misalignment could result in losing the signal entirely.

Mean mark (c) 52%.

ENGINEERING, TE 2020 HSC 20 MC

Which of the following describes high frequency wireless transmission when compared to low frequency wireless transmission?

  1. Faster data rates over longer distances with higher interference
  2. Faster data rates over shorter distances with lower interference
  3. Slower data rates over longer distances with lower interference
  4. Slower data rates over shorter distances with higher interference
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`B`

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  • Higher frequency in wireless transmissions increases data rates
  • However, it decreases wavelength which decreases the penetrating power of a transmission (ie the distance a transmission can travel).

`=>B`

ENGINEERING, TE 2021 HSC 11 MC

Which radio transmission method is most likely to have static interference?

  1. Amplitude modulation (AM)
  2. Frequency modulation (FM)
  3. Digital audio broadcast (DAB)
  4. Pulse width modulation (PWM)
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`A`

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By Elimination:

  • Digital broadcasting will have very little interference (eliminate `C` and `D`)
  • The higher frequency of FM output results in less static than AM (eliminate `B`)

`=>A`