6. A
nonperiodic composite signal has a bandwidth of 200 kHz, with a middle
frequency of 140 kHz and peak amplitude of 20 V. The two extreme frequencies
have an amplitude of 0. Draw the frequency domain of the signal.

__Solution__

The lowest frequency must be at 40 kHz and
the highest at 240 kHz. Figure below shows the frequency domain and the
bandwidth.

7. A
digital signal has eight levels. How many bits are needed per level?

__Solution__

We calculate the number of bits from the
formula,

Number of bits per level = log

_{2}8 = 3
Each signal level is represented by 3 bits.

Note:

8. A
digital signal has nine levels. How many bits are needed per level?

__Solution__

We calculate the number of bits by using the
formula.

Number of bits per level = log

_{2}9 = 3.17
Each signal level is represented by 3.17
bits. However, this answer is not realistic. The number of bits sent per level
needs to be an integer as well as a power of 2. For this example, 4 bits can
represent one level.

9. Assume
we need to download text documents at the rate of 100 pages per sec. What is
the required bit rate of the channel?

__Solution__

A page is an average of 24 lines with 80
characters in each line. If we assume that one character requires 8 bits
(ascii), the bit rate is

100 x 24 x 80 x 8 = 1,536,000 bps = 1.536
Mbps

10. A
digitized voice channel, is made by digitizing a 4-kHz bandwidth analog voice
signal. We need to sample the signal at twice the highest frequency (two
samples per hertz). We assume that each sample requires 8 bits. What is the required
bit rate?

__Solution__
The bit rate can be calculated as

2 x 4000 x 8 = 64,000 bps = 64 kbps

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