Chapter 3: Physical Layer (1)

Question 1

What is Analog Data?

Answer 1

Info that is continuous.

Question 2

What is Digital Data?

Answer 2

Info that has discrete states.

Question 3

What is an Analog Signal?

Answer 3

Infinite many levels of intensity over period of time. Moves through infinite number of values between two values.

Question 4

What is a Digital Signal?

Answer 4

Has a limited number of defined values.

Question 5

What is a Periodic Signal?

Answer 5

Completes a pattern within a measurable time frame, called a PERIOD; repeats pattern over subsequent periods.

Ex: a sine wave

Question 6

What is a Non-Periodic Signal?

Answer 6

Does not repeat a pattern; is irregular.

Ex: a voice speaking

Question 7

What is a Sine Wave?

Answer 7

A periodic analog signal.

Its change over a cycle is smooth and consistent – a single arc above the time axis, a single arc below.

Question 8

What three parameters represent a sine wave?

Answer 8

1. Peak amplitude
2. Frequency
3. Phase

Question 9

What is Peak Amplitude?

Answer 9

A signal’s absolute value of its highest intensity.

Question 10

What is Period?

Answer 10

Amount of time (sec) a signal needs to complete one cycle.

Question 11

What is Frequency?

Answer 11

Number of PERIODS in one second.

Question 12

What is the relationship between Period and Frequency?

Answer 12

Inverses of each other.

period (T) = 1 / freq (f)

freq (f) = 1 / period (T)

Question 13

What is Phase?

Answer 13

Describes the position of the waveform relative to time 0.

Measured in degrees or radians.

Question 14

What is the relationship between degrees and radians?

Answer 14

1 rad = deg * π / 180

1 deg = rad * 180 / π

Question 15

What is Wavelength?

Answer 15

The distance a simple signal can travel in one PERIOD.

Depends on frequency and medium.

Question 16

How do we calculate Wavelength?

Answer 16

Wavelength (λ) = prop speed (c) * period (T)

OR

Wavelength (λ) = prop speed (c) / freq (f)

Question 17

What is Propagation Speed of a wavelength?

Answer 17

Speed at which a wave travels through a transmission medium.

Question 18

What is a Time-Domain plot?

Answer 18

Shows changes in signal amplitude with respect to time.

X-axis is amplitude, y-axis is time.

Question 19

What is a Frequency-Domain plot?

Answer 19

Shows only the peak values and the frequencies.

X-axis is amplitude, y-axis is frequency (Hz).

Question 20

What is a Composite Signal?

Answer 20

A combination of simple sine waves with different freqs, amps, and phases.

Question 21

What is Bandwidth?

Answer 21

The range of frequencies in a composite signal. Bandwidth is measured as the difference between the highest and lowest frequencies of a signal.

Question 22

What is Bit Rate?

Answer 22

The number of bits sent in one second (bits per second).

Question 23

What is Bit Length?

Answer 23

Distance a signal travels during one bit duration.

Question 24

What is the mathematical equation for Bit Length?

Answer 24

Bit length = prop speed * bit duration.

(Bit duration = length of time to transmit a single bit in a digital signal.)

Question 25

What are the two ways we can transmit a Non-Periodic Digital Signal?

Answer 25

1. Baseband
2. Broadband

Question 26

What is Baseband Transmission?

Answer 26

Sending a digital signal over a channel WITHOUT converting it to an analog signal.

Requires a low-pass channel (channel starts at 0 bandwidth).

Use the channel’s entire bandwidth, it’s entire frequency range, to transmit a signal

Question 27

What is Broadband Transmission?

Answer 27

Transmitting a digital signal by first converting it to an analog signal.

Converts digital signals into analog signals of different frequencies, allowing multiple signals to be transmitted without them interfering with each other.