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Day 3

DAY THREE - RADIO TRANSMISSIONS

This day starts with a similar evaluation of the FM Radio Challenge as for the AM Radio Challenge.  Two things should be noticed:  Daytime vs. nighttime doesn't matter as much for FM and FM stations can not be picked up nearly as far away, leading to the question:  What is different between AM and FM radio waves?

Prep Work:

  1. Test FM reception in classroom.  It should be better than AM reception, but it still may be necessary to place the radio by the window.

Materials Required:

  1. Radio
  2. Calculator (for calculation of wavelengths and frequencies)

Class Outline:

Begin class by repeating the previous day's activity, except have the students share their FM stations.

Two questions can then be discussed:

Can they receive all of the FM stations during the day as well as they can during the evening?

Is the furthest nighttime FM reception as far as the furthest nighttime AM reception?

Students should write answers to both of these questions in their notebooks and then share their responses with the class.

 

After this discussion you can start to provide answers to the question:

What's different about AM and FM signals and how they travel?

You should note that FM waves can only travel as ground waves, and, therefore, the distance you can receive an FM signal from is limit by your (our, more specifically, your radio's) ability to "see" the radio transmitter tower.  Once the tower is below your horizon, you lose the station.

However, AM waves can "bounce" off of the ionosphere, and therefore you can "see" them over the horizon!

There is a very simple discussion of this in a web-site maintained by the Louisville Courier-Journal.

There is a wonderful image in the Windows on the Universe discussion of radio wave bands showing the difference between ground waves (FM, TV, and AM) and sky waves (AM).

 

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