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 * 105 complete 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 Hz for 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
Power of 10 3 2 1
1000
100 10
thousands
hundreds
Tens
Units
10^3
10^2
10^1
10^0
Power of 2 3 2 1 8 4
Eights
fours
twos
ones
2^3
2^2
2^1
2^0

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

12. Decimal  binary numbers14
=(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. Number of bits transmitted per second bit rate=data transfer rate
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

20. 14.7 Solve problems involving analogue-to-digital conversion
Pg 400

21. 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

22. 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