Information in Radio Waves

Transcription

1 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: 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

2 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.

3 * 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.

4 Name: Class: Date: Part 1: Frequency: Radio Modulation: Student Worksheet 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:

5 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?

6 5.) Why is Morse Code a useful form of information encoding even today?