Information in Radio Waves
Name: _______________________________________ Class: ________ Date: ________
Basic Radio Modulation: Build Your Own Radio!
Introduction:
Much of today’s technology relies on an invention now over a century old, the radio.
Radio got its beginnings from wireless telegraphy, which like regular telegraphy, used Morse
Code. These were the first and simplest forms of modulation using radio waves but contained
all of the typical parts of even modern radios: a transmitter and a receiver/demodulator.
Wireless telegraphy relied on a binary system of modulation (pulse modulation), either the
signal was on or it was off. Therefore the information sent or received from this type of radio
transmission lay in the timing between the on-off portions of the transmitted signal.
As radio developed the types of modulation used became more and more efficient
(meaning they had a better signal to noise ratio). First came amplitude modulation (AM radio),
where information could be stored and transmitted via radio waves by varying the amplitude of
the sine waves. Then came the even more efficient form of transmission frequency modulation
(FM radio). In FM, the information is stored by keeping the amplitude constant and instead
varying the frequency by a little bit. Since then, there has developed wide-band FM, narrowband FM, HAM radio, digital radio, “HD” radio, etc. For a little bit more basic information about
radio modulation, visit: http://curiosity.discovery.com/question/how-radio-waves-carry-information.
In today’s activity you are going to make two very basic forms of radio. These radio’s
are going to function based on pulse modulation and once you have successfully transmitted a
signal, your next goal will be to successfully transmit an actual message
Materials:
- 9 V batteries
- Nickels
- cheap wire
- metal files
- AM radio(s)
- ruler, 12 inch
Group Size: 2 to 4 students
Learning Goals:
- Familiarization with radio frequencies
- Demonstrate knowledge of basic modulation techniques
- Gain an appreciation for the technology that was available before the digital age
Prior to activity:
- Open up a discussion with the class about what they know about technology during 19th and
early 20th century
- Present to your class some history on radio technology and highlight its basic beginnings as
the wireless telegraph and the first forms of radio modulation
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Methods:
- Part 1 1.) At your working station, get a 9 V battery, a nickel, a ruler, and a working AM radio.
2.) Turn on the radio and tune it to a frequency that is pure static. Record which frequency you
chose.
3.) Hold that battery close to the radio and tap the coin connecting the two terminals of the
battery repeatedly. If you do it correctly you will hear an intermittent crackle. Take turns so
everyone in your group can accomplish this.
4.) Designate one person in your group to handle the battery and the coin, another to manage
the
ruler. Measure the maximum distance you are able to transmit a signal from the battery to
the radio. Record your results.
- Part 2 1.) At your working station, obtain a 9 V battery, a file, 2 pieces of wire, and a working AM radio.
2.) Connect the first piece of wire to the handle of the file. Connect the other end of that wire to
one of the terminals on the 9 V battery.
3.) Connect the second piece of wire to the open terminal of the battery.
4.) Once everyone in the class has the setup complete, have the teacher turn off the lights in the
classroom. Once off, run the open end of wire along the file. Record what you see. Turn
lights back on when finished with this.
5.) Turn on the radio and tune it to a frequency that is pure static. Record which frequency you
chose.
6.) Hold the file close to the radio and run the open end of wire along it. Record what you hear.
7.) Again, using a ruler, measure the maximum distance this simple radio can transmit. Record
your results.
- Part 3 1.) Obtain the “International Morse Code” handout.
2.) Have each person in your group make up a unique message at least 3 words in length (do
not share your message with the other members of your group).
3.) Translate your messages into morse code (written).
4.) Determine which version of radio that you made you want to use. When ready, take turns
transmitting your message to the other members of your group using morse code.
Tip - the batteries may run out pretty quickly doing this, if this happens or you can’t get it
to work transmit the messages using a pencil and the table/desk
- Record the messages from each of your group members and check for accuracy.
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* Feel free to use the timing described above or use your own version. Longer spacing between letters and words may be required
for beginners in Morse Code.
Information in Radio Waves
Name: ________________________________________ Class: _________ Date: _________
Radio Modulation: Student Worksheet
Part 1:
Frequency: ___________
Drawing of radio setup. Describe its parts and how/why it works.
Maximum distance of transmission: ___________________
Part 2:
Frequency: ___________
Drawing of radio setup. Describe its parts and how/why it works.
Maximum distance of transmission: ___________________
Part 3:
You Secret Message:
____________________________________________________________
Your message translated into Morse Code:
Information in Radio Waves
Group members messages:
1.)
_____________________________________________________________________
2.)
_____________________________________________________________________
3.)
_____________________________________________________________________
Discussion Questions:
1.) Which type of simple radio was it easier to make a signal with? Which type produced the
better signal?
2.) What was the maximum distances you were able to transmit a signal? Why could it not
transmit further?
3.) Why could you turn to any part of the AM spectrum and still get a signal from the battery?
What did you see in Part 2 when the lights were off? How are these to things related?
4.) What type of modulation was used in the radios that you made? How does this type of
modulation work? Where is the information in the transmission?
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5.) Why is Morse Code a useful form of information encoding even today?