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).
 Solve problems based on the modulation of the carrier
wave in order to determine the frequency and the
amplitude of the information signal.
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
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
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
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.
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.
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.
Communications
14.2 Digital Signals
14.1 Solve problems involving the conversation
between binary numbers and decimal numbers
Power of 10
Power of 2
3
2
1
0
1000
100
10
1
thousands
hundreds
Tens
Units
10^3
10^2
10^1
10^0
3
2
1
0
8
4
2
1
Eights
fours
twos
ones
2^3
2^2
2^1
2^0
Convert the following binary numbers into
base 10 (to decimal numbers)
1001011(2)
=(2^6)+(2^3)+2+1
=64+8+2+1=75
Decimal  binary numbers
14
=(8+4+2)
=2^3+2^2+2^1
=1110(2)
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
14.3 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
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
Analogue data
transmission
clock
ADC
Analogue to
digital converter
modulator
Parallel to serial
converter
Carrier wave
Converts
bytes to
pulses
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
 Nyquist theorem=sampling theory
 To ensure accurate reproduction of the signal must be
equal to, or greater than twice the signal frequency
14.6 Describe what is meant by timedivision multiplexing
 Time division multiplexing
14.7 Solve problems involving
analogue-to-digital conversion
 Pg 400
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
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