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 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

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 clock ADC Analogue to digital converter Analogue data Parallel to serial converter modulator transmission Converts bytes to pulses Carrier wave

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

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 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