Module 2

Question 1

What three characteristics does a signwave have?

Answer 1

Amplitude, Frequency and Phase.

Question 2

Is the voltage of a battery constant?

Answer 2

The voltage of a battery is constant.

Question 3

What characteristics of a signal are changed in communications?

Answer 3

Frequency, Phase and Amplitude.

Question 4

A transmission medium can pass only some frequencies not all. What does this mean?

Answer 4

This means that we must change the baseband signal so that it can be sent across the given medium.

Question 5

A signal has a spectrum with frequencies between 1000 and 2000 Hz (bandwidth of 1000 Hz). A medium can pass frequencies from 3000 to 4000 Hz (a bandwidth of 1000 Hz). Can this signal faithfully pass through this medium?

Answer 5

Yes it can but the baseband has to be up converted to be transmitted in the range 3000 to 4000 Hz.

Question 6

Why does a digital transmission need a low pass channel with a very wide bandwidth?

Answer 6

This is because square waves (digital) are composite signals composed of very low to very high frequencies.

Question 7

How to send digital information on a band-pass channel?

Answer 7

Encode the digital signal so that it can be sent across the medium.

Question 8

Relate the bandwidth of a signal and the bandwidth of a transmission medium when data is transmitted.

Answer 8

Bandwidth in Hz is the range of frequencies contained in a composite signal or the range of frequencies a channel can pass.

Bandwidth in bps is the bits per second (i.e., the data rate) that a channel or a network can transmit.

Question 9

Use Nyquist bit rate and Shannon capacity formulas to determine the appropriate bit rate and signal level when a channel is given.

Answer 9

Nyquist
BitRate = 2 × Bandwidth × log2L

Shannon Capacity
Capacity = Bandwidth × log2(1 + SNR),

Question 10

Use decibel to calculate the attenuation of a signal.

Answer 10

dB = 10 × log10(P2/P1)
Decibel numbers can be added (or subtracted).

10log10(P2/P1)
10log10(.5/1) = -3dB

Question 11

Use Nyquist bit rate and Shannon capacity formulas to determine the appropriate bit rate and signal level when a channel is given.

Answer 11

Nyquist
BitRate = 2 × Bandwidth × log2L

L = number of signal levels

Shannon Capacity
Capacity = Bandwidth × log2(1 + SNR),