Communication Technology
Developing and Using Models
Digital Wave Signals in Modern Communications
Team Name______________________________________
Team Members:
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Communication Technology
Digital Wave Signals in Modern Communications
Goal: To develop a model to show how electromagnetic waves are used in
communication
Part 1: Model Set-up
1. Two teams of four (4) students will work with one long wave spring
2. Each team with arrange themselves at opposite ends of the spring in four
different positions (see the Figure below):
Group 2
4
3
2
1
Group 1
4
2
3
1
3. Student #1 is called the “transmitter” (wave generator). Their role is to
produce a wave that will travel along the spring
4. Student #2 is the anchor (sits at the half way point along the spring with
their backs to the #2 student from the opposite group). Their role is to act as
the end point for the wave that will travel towards them. They should grasp
the spring tightly at that anchor point and make sure the wave does not
travel onto the other teams side of the spring
5. Student #3 is called the “receiver”. They should position themselves
somewhat closer to the anchor end of the wave spring. They will place their
hand about 20 cm from the spring, pinky down, thumb up, with the palm
facing the spring. They need to be able to “sense” the wave hitting their palm
as it passes by their hand because they will be blindfolded the entire time
6. Student #4 is called the “processor” (image generator). Their role is to
translate the incoming message (the wave) into an understandable output
message
7. Students will switch between all four positions during the activity
Part 2 – How To Use the Model
1. Stretch out the spring and position both teams in their respective places
2. Student #1 (transmitter) generates a sideways wave pulse with a rapid flick
of the wrist to the side. If the student rapidly moves his or her wrist only
about 10 cm to the right, then the wave pulse generated will have an
amplitude of approximately 10 cm. By changing the amount of motion of the
wrist, the student can generate different amplitudes of wave pulses that
travel down the spring
3. Every time a wave pulse in sensed by the receiver, he or she should raise a
finger in the air. The image generator will then mark a tally down on a piece
of paper. Tallies should be kept for the number of waves generated as
well as the number of waves received
4. Because the receiver needs to sense the wave pulse, it is a good idea for the
team to practice the model a few times so that this happens reliably
5. The spring represents an electromagnetic wave—an invisible wave of
interacting electric and magnetic fields—but this model makes those
waves visible
6. Practice using the model and have your team rotate through all of the
positions until everyone is comfortable transmitting, receiving, and
generating an image of the wave pulse
7. Practice using the model to send more complicated pulses along the spring (2
pulses quickly; 2 quick pulses followed by 2 drawn out pulses; can the
receiver count even more pulses like 4-5 rapid pulses?; larger or smaller
amplitude)
Part 3 – A Digital Stream
1. What does digital mean (in terms of describing messages)? (answer the
question in your Google docs file)
2. For Part 3, all waves will only communicate one or two possible values. One
pulse equals a value of 1; 2 quick pulses right after each other equals a value
of 0 (this corresponds to the usual values for digital signals, 1 and 0, instead
of 1 and 2)
3. Do not think of 0 as meaning nothing was sent. Instead, think of the two
quick pulses as cancelling each other out
4. The amplitude of the pulses do not matter as long as they are large enough to
be easily sensed by the receiver
5. The fact that digital signals are received either as a 1 or a 0, what do you
think that would mean in terms of the quality of the signal? (Google doc
and share)
6. Students should return to their group positions at the spring. The transmitter
should write down a random 10-digit sequence of 1’s and 0’s. Do not let the
receiver or image generator see the sequence (remember the receiver needs
to be blindfolded)
7. Transmitter should then start to send the signal down the spring. Wait for
the receiver to receive the signal before sending a new signal. Remember, 1
pulse =1; 2 quick pulses = 0)
8. When the signal is received, the receiver says loudly either 1 or 0. The
response is recorded by the image generator
9. After the last signal is sent, the transmitter says “End of Message”
10. When the completed sequence has been received and recorded, the blindfold
can be removed and all students should compare the intended message that
was sent to the actual message that was recorded by the image generator
11. Students should switch roles so that everyone has a chance at each role
(Answer these questions in Google docs and share with me)
12. Describe the function of each of these “communication with waves”
model components: transmitter, receiver, image generator
13. What is the underlying purpose of using models in science? Use the
wave communication model as an example in your explanation
Part 4 – Digital v. Analog Communication
1. Analog signals are not based on the number of pulses but on the amplitude of
each pulse (wave). AM means “amplitude modulation”; radio signals work
this way
2. Transmitter should write down a random sequence of different size wave
amplitudes to send down the spring. Do not let the receiver (blindfolded
again) or the image generator see the sequence (Ex.: 20cm; 40cm; 10cm;
60cm)
3. Transmitter should begin sending this analog message down the spring.
Larger amplitude waves can be sent be simply flicking the wrist with greater
power
4. Receiver should attempt to guess the amplitude of the pulse by how hard it
hits their palm. The image generator should write down what the receiver
guesses
5. After the last pulse the transmitter should say “End of Message”
6. When the completed sequence has been received and recorded, the blindfold
can be removed and all students should compare the intended message that
was sent to the actual message that was recorded by the image generator
7. Students will notice that it is very difficult to correctly guess the amplitude
intended in the message. This is called static in the signal
8. Let’s look at an important historic television transmission and see how it
compares to today’s television signals
9. Describe the differences and similarities between digital and analog
signals. How are they sent and received? What about the clarity of each
type of signal? (Google docs and share)
Part 5 – A Low-Resolution Letter
1. The next transmission will send the letter X (see Figure 4) rather than a
random stream of 0 and 1 digits. Be aware of the sequence for putting either
a 0 or a 1 in each of the boxes in a 3 × 3 grid, which is typically done left to
right, from top row to bottom. 1’s are shaded; 0’s are left white
2. The streams of 0s and 1s would be recorded by the image generator in a 3 ×
3 box they have drawn on grid paper, rather than recording the stream in
one long, continuous line. A nine-digit stream of 0s and 1s will fill this 3 × 3
grid, with each 1 represented by a shaded cell and each 0 represented by a
white cell.
3. After successfully sending the letter X, your team will send out a few more
low-resolution letters to each other. Taking turns with each role, student #2
creates a letter in a 3 × 3 grid by shading in cells to make a letter, such as
those shown in Figure 5 (Do not reveal the letter to the receiver or image
generator)
4. The transmitter then generates the nine-digit code for the letter, and that
code is sent to the receiver, who then tells the image generator whether to
record a 0 or 1 in the “message grid,” which is simply a blank 3 × 3 grid on
the paper being used by the image generator
5. After the image generator shades in all of the 1s transmitted, the message
grid should be the same letter as the one originally sent (see Figure 5)
6. Practice sending other letters not listed
Part 6 – A High-Resolution Letter
1. It should quickly become apparent that you will need to use grids bigger than
3 × 3 to send a higher resolution letter. In fact, the more squares in the grid,
the more resolution (for example, see Figure 6, the letter X on a 5 × 5 grid).
Each square on the grid is called a pixel (picture element)
2. Rather than having your team actually send many of those signals via the
spring-wave model, having them understand how it works and that
computers are able to send such streams of 0s and 1s really, really fast might
be more fruitful
3. Work with paper representations of the text or images they would send
rather than actually sending them with the wave model
4. Practice constructing grids (size is up to you) for letters of your choice.
Each member of your team should submit an different letter (draw the
grids on graph paper and submit them when you are finished)