Chapter 2

Wireless Data Transmission

Lab 2-1 Data Representation Practice

Objectives

This lab is designed to help you become familiar and comfortable with the mechanisms used in computers to represent data.

After completing this lab, you will be able to:

Convert characters and words from or into ASCII code

Describe how binary numbers are used to represent data

Materials Required

Pen or pencil and paper

A computer with Internet access

Estimated completion time:

15 minutes

Activity

Using the Internet locate a Web page that contains an ASCII table that shows both the decimal and hexadecimal values for each letter of the alphabet in both uppercase an lower case (A-Z and a-z), and for each decimal digit (0-9).

Write your first name in ASCII using the decimal values equivalent to each character. You can use all capitals, all lower case, or a combination of both.

Write your first name as above but using the hexadecimal equivalent values for each character.

Review Questions

What is Unicode?

List one other type of code that has been used for representing data (other than ASCII, or Unicode/UTF-8):

Computers can store numbers in binary or in text format using a code like ASCII or UTF-8. Write your age below in ASCII hexadecimal, then convert the hexadecimal to a binary representation of the code.

Why do we use a hexadecimal representation of ASCII, instead of decimal?

Explain in one short sentence why light is considered part of the Electromagnetic Spectrum:

List the frequecy band ranges for infrared light and visible light (hint: you can find sources of information on the Internet):.

Lab 2-2 Analog Transmission

Objectives

This lab is designed to help you visualize the different types of analog transmission.

After completing this lab, you should be able to:

Visualize and draw an example of an amplitude modulated signal

Visualize and draw an example of a frequency modulated signal

Materials Required

Pencil and eraser, if using the space provided below

Optional: graph paper

Estimated completion time:

30 minutes

Activity

Using the grid provided below or a separate sheet of graph paper, draw an example of a 4 Hz analog wave modulated in amplitude by the analog signal that is already drawn on the grid. Use the examples in the book to help you!

Input signal

Using the frequency modulated wave below, draw an approximation of what an analog input signal that was used to modulate the wave would look like, within the gridlines below it. Note that there are three different frequencies in the graphic. Begin drawing from the zero volts line.

Review Questions

What is the frequency of an analog signal in which has 300 complete wave cycles occurring every second?

What happens when a signal reaches an antenna designed to receive signals of the same frequency?

Explain the difference between bit rate and Baud rate:

What is the frequency and wavelength of the musical note E1? Hint: The musical note E1 is a soundwave, not an EM wave and sound travels through air at approximately 343 meters per second.

Write down the frequency in MHz and wavelength in centimeters of a signal which has 2,412,000,000 complete wave cycles occurring every second:

Lab 2-3 Digital Signals

Objectives

This lab is intended to help you visualize how a character is encoded before transmission using digital signaling techniques.

After completing this lab, you will be able to:

Describe how different methods of digital modulation work

Draw examples of different encoding methods

Materials Required

Pencil and eraser, if using the space provided below

Optional: graph paper

Estimated completion time:

45 minutes

Activity

Using the hexadecimal ASCII code for the first letter of your first name, draw the equivalent binary signal using the NRZ method.

Using the hexadecimal ASCII code for the first letter of your first name, draw the equivalent binary signal using the NRZ-L method.

Using the hexadecimal ASCII code for the first letter of your first name, draw the equivalent binary signal using the NRZ-I method.

Using the hexadecimal ASCII code for the first letter of your first name, draw the equivalent analog signal using phase modulation.

Review Questions

The number of transitions in a digital signal affects how efficiently it can be transmitted using an analog signal. Which of the digital signals in activities 1, 2, and 3 in Lab 2-3 above has the fewest transitions?

An analog signal that is modulated with, for example, an audio signal is generally called a ___________ wave.

What is the effect of applying a barker code (or chipping code) on a digital signal, before transmitting it using an analog signal?

How does narrow band interference affect a FHSS transmission?

Conversely, how does a narrow band signal interfere with a DSSS transmission?