MISSION PLAN
Space Radio Communications
1.
GENERAL
This class will familiarize the Mission Team with radio fundamentals and develop a basic
understanding of use of radios in space. This class is presented to expand the terrestrial and
space knowledge of all Galaxy Explorers in order to enhance their competence and confidence of
all aspects of space.
2.
LEARNING OBJECTIVES
SUBJECT AREA: Space Radio Communications (Engineering)
TASK: Explorers will understand radio transmitters, antennas, receivers and radio wave
propagation. Explorers will be acquainted with the uses of radio technology in space.
CONDITIONS. (Put here what you are giving the student to perform the Task (e.g.
handouts, book).
STANDARD. Must demonstrate an understanding of the following: transmitters,
antennas, & speakers. Must describe how radio waves are propagated through space. Must be
able to recite at least three ways radios are used in space.)
3. PRESENTATION GUIDE
a. Introduction (_20_ minutes) (Show any training aid(s) needed)
Good afternoon, I am ___Your Name here___ and I will be your teacher for Space
Communications. We are going to explore radio fundamentals and discuss how radios are used
on earth and in space. We will talk about how radios signals are transmitted, how they travel
through space, and how the signals are received. While radios are very complex, the
fundamentals are fairly simple. We will cover this material very quickly, so please ask
questions. If you are really interested in radio, there is some excellent information on the
Internet.
b. Development (__20__ minutes) MAIN LECTURE
Slide 1: Today we are going to talk about radios in space. We all use radios every day of one
sort or another. We listen to music on our car radios, but there are many other forms of radio
that we use such a cell phones, garage door openers, radio controlled toys, and television. There
are many used for radios in space. Who can tell me some of the ways we use radios in space?
{Make a list on the whiteboard.}
Slide 2: This is a list of the some of the ways radios are used in space. {Compare with the list on
the whiteboard complimenting any additions not on the slide.} Talking to astronauts is pretty
obvious. We also need to talk or communicate with unmanned satellites. For example we need
to tell an imaging satellite where to take pictures and then have the satellite send us the images.
There is a system of satellites called “Global Positioning Satellites” or GPS for short. We use
GPS to tell us where we are, both on the ground and in space. We have many communications
satellites that sort of act like mirrors bouncing signals from one spot on the earth to another. For
example, a telephone call from Europe would go through such a satellite. Obviously, radios are
very important in space as they are on the ground. So, how do they work? Let’s look some of
the fundamentals of radio.
Slide 3: Who has thrown a rock into the water and watched the circles of waves spread out
across the surface? The circles on the water just get bigger and bigger. They also seem to get
weaker and weaker as they spread out until they disappear altogether. Radio waves travel
outward in the same way except they go on forever unless they hit something. The radio
broadcasts in the early 1920s are now 80 light years out in space since radio waves travel at the
speed of light. I wonder if anyone out there is listening? What so you think? Radio concepts
are pretty simple, but you need to understand a few things like wavelength and the
electromagnetic spectrum. Let’s start with wavelength. Picture the waves traveling out from the
rock you threw into the water. If you looked along the surface the waves would look like this
wavy graph on the slide. The wavelength is simply the distance from one part of the wave to the
next identical part, such as the distance between the crest as shown here. Let’s say we measured
the distance between the waves on the water and the wavelength was three inches. That is the
length of the radio waves of our cell phones!
By the way, we can talk about radio signals in terms of either wavelengths or frequencies since
the wavelength times the frequency of a signal equals the speed of light. That is, the higher the
frequency, the shorter the wavelength.
Slide 4: What’s this?! We seem to be mixing radio waves up with a lot of other stuff like light
and X-rays. Actually, they are all the same, technically referred to as electromagnetic radiation.
We classify these electromagnetic waves according to wavelength as pictured here. Our eyes are
sensitive to the colors in the rainbow, but there are many other colors we cannot see. Snakes for
example see longer wavelengths than we do in the infrared. Honeybees see shorter wavelengths
in the ultraviolet. Of course, we are all familiar with X-rays that are so short they go right
through us except for our bones so we can see how badly we have broken our arms or whatever.
For radio, we are talking about the longer wavelengths such as radio and microwaves. That is
the part of the electromagnetic spectrum we use for communicating by radio.
The next two slides are challenging, so pay close attention.
Slide 5: To communicate by radio we need a transmitter and a receiver. Your cell phone has
both, but let’s look at just the transmitter part. You have a microphone that transforms sound
into electronic signals. These signals are weak so we pass them through an amplifier to make
them stronger. Now pay attention since this is the hard part. We need to be able to sort out the
signal we receive from all the electromagnetic radiation out there. We do this by transmitting on
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a particular wavelength (carrier wave) usually referred to as a channel. We use an oscillator to
generate the strong carrier wave and then mix this signal with the voice signal in a thing called a
modulator. This signal then goes to an antenna where the electrons antenna move up and down
changing the magnetic field around the antenna in response to the signal. These changes in the
magnetic field cause radio waves to travel out from the antenna.
Slide 6: A radio receiver is pretty simple and sort of works in reverse of the transmitter. The
radio waves striking the antenna cause electronic signal to be created. Since we are only
interested in a particular signal, we tune our receiver to the selected carrier wavelength. This
tuner works sort of like the oscillator in the transmitter only in reverse. But we don’t want to
listen to the carrier signal, so we use a detector circuit to strip out the voice signal. We amplify
that signal to make it stronger and send it to the speaker so we can listen.
Slide 7: Let’s lighten up a bit and look at some pictures. This slide shows the anatomy of a
satellite. The green things are the communication parts: transmitter, receiver and antennas. This
is an imaging satellite and the camera is this purple thing. This high gain antenna sends the
image down to the ground.
Slides 8-12: These are pictures of different kinds of satellites. Notice how different the antennas
are on each satellite. That is because they are used to do different things and they transmit and
receive on different wavelengths.
Slide 13: Remember that radio astronomy was one of the uses we listed for radios in space. This
is a picture of a group of radio astronomers and their antennas.
Activity 1:
• Take a fresh 9-volt battery and a coin.
• Find an AM radio and tune it to an area of the dial where you hear static.
• Now hold the battery near the antenna and quickly tap the two terminals of the battery
with the coin (so that you connect them together for an instant). The interruption of the
electricity going through the coin causes weak radio waves.
• You will hear a crackle in the radio that is caused by the connection and disconnection of
the coin.
• If you click the coin at different rates, you can send a message in code.
• Notice that as you move the coin and battery away from the radio, the clicking goes
away. That is because the coin is a very poor antenna and the battery provides very low
power.
Activity 2:
• Connect wires to each terminal of a fresh 9-volt battery.
• Connect one of the wires to the handle of a metal file.
• Now scrape the end of the second wire along the file while you are holding it next to an
am radio. You should hear lots of static.
• If you do this in the dark, you can small sparks between the end of the wire and the file as
you scrape it along.
Activity 3:
Slide 14: Use a spring (or rubber band) and a weight to demonstrate a mechanical analog of an
oscillator used to tune into a radio station
• Use a screen door spring and several weights of different sizes to show how the
frequency of the mechanical oscillator changes with the different weights.
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4.
Put the heaviest weight on the spring and bounce it up and down to find the natural
frequency of the mechanical oscillator.
Move the top of the spring up and down faster than the natural frequency. The weight
doesn’t move much because the oscillator is not tuned to that frequency. That is why a
radio only picks up the station (frequency) it is tuned to. The radio only picks up the
station broadcasting on the frequency of its electrical oscillator.
Place the lighter weights on the spring (one at a time) and observe the effect on the
frequency (faster) it moves up and down. Turning the knob on the radio changes the
frequency of the electrical oscillator just like changing the weight does on the mechanical
oscillator.
TRAINING AIDS
Refer to the corresponding Power Point file for the slides.
5.
LISTING OF TRAINING AIDS (Examples)
a.
b.
c.
d.
e.
f.
g.
h.
Overhead view graphs
AM radio
9-volt battery
Piece of metal long enough to short out the 9-volt battery
Metal file
2 wires to connect file to battery
screen door spring
weights of different sizes
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