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Communications

Communications. IB physics. 14.1. Describe what is meant by the modulation of a wave. Distinguish between a carrier wave and a signal wave. Describe the nature of amplitude modulation (AM) and frequency modulation (FM).

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Communications

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  1. Communications IB physics

  2. 14.1 • Describe what is meant by the modulation of a wave. • Distinguish between a carrier wave and a signal wave. • Describe the nature of amplitude modulation (AM) and frequency modulation (FM). • Solve problems based on the modulation of the carrier wave in order to determine the frequency and the amplitude of the information signal.

  3. What is a modulation of a wave? • Changing the amplitude or the frequency of a wave in respect to time, is called modulation of the wave. • This will change the information of the wave. Modulation of a wave

  4. Distinguish between a carrier wave and a signal wave. • Carrier wave: The original wave • Signal wave: The superimposed wave • The radio spectrum covers a range of frequencies varying from about 3 kHz to 300 GHz. • The carrier wave below would be a radio frequency wave and if audio data is being transmitted, the signal wave would be an em wave that is in the audio frequency range

  5. Describe the nature of amplitude modulation (AM) and frequency modulation (FM). • AM: In amplitude modulation, the frequency of the carrier wave is constant and the signal wave is used to vary the amplitude of the carrier wave. The amplitude of the analogue wave (voltage) is being varied

  6. Frequency Modulation • In frequency modulation the amplitude of the carrier wave is kept constant and the signal wave is used to vary the frequency of the carrier wave.

  7. Solve problems based on the modulation of the carrier wave in order to determine the frequency and the amplitude of the information signal. • Example) a carrier wave is modulated by 1 signal wave. The result of the modulation yields a max amplitude occurring at every 2.3ms on the carrier wave. Between each max amplitude there are 2.1 * 105complete oscillations. Determine the frequency of the signal wave and of the carrier wave.

  8. Solution • For the signal wave 1/fs = 2.3×10-3 • fs =1/2.3×10-3= 435 Hzfor the carrier wave fc= (2.1× 105)/(2.3×10-3)=9.1 × 107= 91 MHz • Example2) If the carrier wave in the above example is frequency modulated by the same signal wave as above, determine the time interval between an oscillation of the carrier wave of maximum frequency and one of minimum frequency.

  9. Communications 14.2 Digital Signals

  10. 14.1 Solve problems involving the conversation between binary numbers and decimal numbers

  11. Convert the following binary numbers into base 10 (to decimal numbers) • 1001011(2) =(2^6)+(2^3)+2+1 =64+8+2+1=75

  12. Decimal  binary numbers • 14 =(8+4+2) =2^3+2^2+2^1 =1110(2)

  13. 14.2 Distinguish between analogue and digital signals • 有 Continuous variation analogue • Signals continuously changing from one amplitude to another • Continuous variation X …either high or low • digital

  14. 14.3 State the advantages of the digital transmission, as compared to the analogue transmission, of information • Noise= when affected by noise, information is unaltered • Source independence= independent of what type of into is transmitted…speech text video all in same signal • Bandwidth & Compression= compressing does not change the info just enables it to transmit quickly • Transmission rate, multiplexing, coding, data manipulation

  15. 14.4 Describe, using block diagrams, the principles of the transmission and reception of digital signals Sample data converted into “bytes” Provides the reference pulses Sample and hold clock ADC Analogue to digital converter Analogue data Parallel to serial converter modulator transmission Converts bytes to pulses Carrier wave

  16. 14.5 Explain the significance of the number of bits and the bit-rate on the production of a transmitted signal • Number of bits transmitted per second bit rate=data transfer rate • Bit rate= number of bits per sample * sampling frequency • Greater the bit rate, higher the quality of the reproduced transmitted data

  17. Nyquist theorem=sampling theory • To ensure accurate reproduction of the signal must be equal to, or greater than twice the signal frequency

  18. 14.6 Describe what is meant by time-division multiplexing • Time division multiplexing

  19. 14.7 Solve problems involving analogue-to-digital conversion • Pg 400

  20. 14.8Describe the consequences of digital commutation and multiplexing on worldwide commutations • The amount of information and the speed with which it now can be transmitted across the world…very very fast

  21. 14.9 Discuss thee moral, ethical, economic and environmental issues from access to the internet • Can spread political or religious propaganda • Illegal goods sold • Pornography for minors • ‘internet shopping’ and its effect economically and socially • World’s energy consumption

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