Communication

Question 1

Compare ad-/disadvantages of wire pairs vs. coaxial cables.

State the function of the copper braid in a coaxial cable.

Answer 1

Wire Pairs:

• cheaper
• higher attenuation (cross-linking/-talk)
• more noise/interference
• low security
• low bandwidth

Coaxial Cable Braid:

• shielding
• acts as return for signal

Question 2

Define signal Modulation.

Answer 2

Variation of amplitude or frequency in a carrier wave to make a signal wave intelligible.

Question 3

Define Amplitude Modulation.

Answer 3

Carrier wave’s amplitude is made to vary in synchrony with the signal wave’s displacement (no change in frequency).

Question 4

Define bandwidth.

Answer 4

Range of signal frequencies in a modulated carrier wave (2signal frequency) (bandwidth of audio = 0.5total signal bandwidth (bandwidth of one sideband))

Question 5

Define Frequency Modulation.

Answer 5

Carrier wave’s frequency made to vary in synchrony with signal’s displacement (no change in amplitude).

Question 6

State the effects an increased signal bandwidth would have.

Answer 6

• less distortion
• higher rate of data transfer
• better signal reproduction quality
• fewer possible transmissions/stations in limited frequency range

Question 7

State pros and cons of AM transmission.

Answer 7

Pros:

• low bandwidth (more stations can transmit in frequency range)
• high area coverage per transmitter
• cheaper radio sets

Cons:

• requires high-power transmitter
• much noise & interference (e.g. lightning strikes can vary amplitude)

Question 8

State pros and cons of FM transmission.

Answer 8

Pros:

• less noise & interference
• greater bandwidth (better sound quality)

Cons:

• shorter range
• more expensive/complex circuitry

Question 9

State advantages of digital transmission vs analogue.

Answer 9

• signal can be regenerated to eliminate noise
• data can be added to check for transmission errors
• multiplexing is possible (same pathway used for multiple signals simultaneously)
• data easily encryptable

Question 10

Describe the process of Analogue/digital interconversion.

Answer 10

• Analogue voltage sampled at regular frequency (f prop. to step width^-1 and max. reproducible freq. of signal)
• converted to binary value (number of bits prop. to step height^-1 and intensity resolution)
• to change from/to digital signal, serial/parallel converters are needed (one channel to measure/reproduce each analogue “bit” digit)

Question 11

State why regeneration of analogue signals is not possible.

Answer 11

• continuous
• noise superposed on signal (indistinguishable)
• noise and signal amplified by same factor

Question 12

Define attenuation.

State formulae for:
Amplification
Attenuation
Signal to noise ratio plus attenuation

Answer 12

Attenuation -> gradual decrease in signal’s power with distance travelled
Amplification (dB) = 10log(Pout/Pin)
Attenuation (dB) = 10log(Pin/Pout)
STN+attenuation (dB) = 10log(Pin/P(noise)out)