Try It At Home! Be an
Interference Detective!
In the universe,
accelerating electric charges make radio waves. (Lightning is an awesome
example of an accelerating charge!) Humans make use of this fact. For example:
Oscillating charges make radio waves at a radio station. Radio Astronomers call
man-made radio waves “interference”.
Interference means trouble for radio astronomers! Interference makes it hard to detect the
much weaker radio waves emitted by objects in the universe.
Make and detect interference! Look for
interference in your home !
What
you need:
a radio - preferably a portable one - that has an AM and FM
dial.
small batteries ( if you raid the flashlight - don’t forget
to put them back!)
a piece of wire
What
to do:
Turn on your radio.
Choose AM and find a place low down on the dial where there are no stations.
What do you notice?
Can you hear anything? _____________________________
Record the Dial
setting: _____________________kHz____
Tape one end of the
wire (it needs to be bare) to one end of the battery. Or just hold it there.
Touch the other end of the wire to the other end of the battery. What do you
notice? __________________________
Try an experiment: Change the dial on the radio and repeat the battery experiment. Is the interference better or worse?
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Dial Setting (kHz) |
Interference Noise (1 = soft, 5 = loud) |
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Try the FM dial.
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Dial Setting (MHz) |
Interference Noise (1 = soft, 5 = loud) |
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How does the FM interference compare with the AM? Predict the interference level that could be detected by a shortwave radio.
Look for Interference in your
neighborhood:
This is where it is
nice to have a portable radio. Turn it
on ( AM or FM - you decide!) and listen as you try different things. You can try:
• Light switches,
remote control cars, electric shavers, microwave oven, computer, TV
• Get your parent to
turn on the car. Try windshield wipers,
turn signals.
• Listen to different small motors: blenders, food processor, weed eater (You should wear earphones so you can hear)
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Object Tested |
Description of Interference |
Interference Noise Level |
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Extensions:
1. Make quantitative
measurements: If you have a voltmeter
at school, you can plug it into the headphone jack on the radio .
2. If your PC has a
sound card, you can view a spectrum of it. Record the interference on tape and store it on your computer. You can obtain shareware PC spectrum analyzer
software from http://www.visualizationsoftware.com/gram.html
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