Long-Distance Data Transmission

Background/Rationale

The video images your students will be seeing are beamed back from Antarctica to your classroom by an elaborate network. Infrared lasers, microwave transmitters and receivers, satellites and fiber optics all play a part in passing along the data that will become the television program you will be watching. In the first Video, your students will be introduced to the satellite uplink procedure and the network of people who make it possible. This Activity presents them with an opportunity to participate in an analogous process of signal transmission and reception by using light to send data across space and around obstacles.

Objectives

Vocabulary

Materials (for each team of 4 students)

Optional:

Optical fiber (in some locations, this may be available from Radio Shack or other hobbyists' stores; or request scrap lengths from your local phone company) Laser (if accessible and safety considerations allow) or Build a Laser by taping over the lens of a powerful flashlight, except for a small, clear spot which can be pressed up against the fiber optic cable.

Preparation

Gather your materials. Each team will need a set of two pieces of the paper with the 4 x 4 grids, to record the message to be sent and then what was actually received, one flashlight and at least two mirrors. Several feet of fiber optic cable and a laser (instead of the flashlight) make nice additions for the higher grades. Form student teams of 3 or 4 each. Have one student per team create a message to be sent by filling in squares to create a pattern on the 4 x 4 grid.

DON'T LET THIS BE SHOWN TO OTHER MEMBERS OF THE TEAM!

Class Activity

  1. Ask students to imagine what combination of tools the NASA/PBS team uses to transmit live pictures from Antarctica to the television in your classroom. Tell them that they themselves will simulate a satellite uplink from a distant location, around the curve of the planet.
  2. Have several students help you demonstrate how to transmit a sample image which you have created. They first must decide how to "encode" the message (for instance, two flashes per second means a filled square, one flash/sec means a blank square) and in what order to send the information (for instance, the first transmission will be for the top left-hand square of the "receiver, next will be the next square down on the left of the grid, etc.) Students who make mistakes can be reminded that signal noise is also a problem for real satellite transmissions.
  3. The first student uses the flashlight to send the message to the second student, who reflects it on to a third student, who then bounces it on to the fourth and last, who tries to reproduce the initial image by filling squares on the second 4 x 4 grid paper, one square at a time. When the first student has sent all his or her squares, compare the two patterns. (Note: that the cumulative filling in of squares on a grid is essentially a very slow but rather similar process to that by which a television picture is built up, one pixel at a time.)

Wrap Up

Discuss what each student represents. The student with the flashlight is the microwave transmitter, the students with the mirrors are the intermediate satellites, the receiving student is the microwave receiver. What caused problems in reproducing the message faithfully? What are the real-world problems? (poor weather, misaligned satellite dishes, satellites drifting in orbit, etc.)

Extensions

Assemble the students into larger teams and direct them to establish a transmission method that puts all of them to work, bouncing the signal further, around corners, up and down stairs, in from outside the classroom, etc. When they have a network in place, give them an unfamiliar 4 x 4 image for transmittal. At the completion of the exercise, the transmitted and received messages are compared. If you have space, a timed contest between teams, with points off for "errors" might be considered. If there's time, do it all again, but reversing the chain (receiver is now transmitter).

Have students make a chart showing their method of data transmission; compare and contrast with the NASA/PBS system, as shown on the reverse of the 4 x 4 copy master provided in this pack.

Follow Up Discussion/Journal Entry

Have students list questions they would like to ask an Antarctic researcher using such a network.

Options

Have teams of students research the component parts of the network used by NASA: infrared lasers, microwave transmitters and receivers, satellite uplinks and downlinks and optical fiber. Have them determine how the signal they watched at their school got to them from WHRO in Virginia.

Follow Long Distance Data Transmission, with Build A Robot out of Humans.

This lesson adapted from the "Life From... Other Worlds" Teacher's guide.

November 1993 GHSP/INNERSPACE FOUNDATION
THE "LIVE FROM... OTHER WORLDS" PROJECT
PROJECT DIRECTOR & EXECUTIVE PRODUCER Geoffrey Haines-Stiles