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Introduction
This unit describes the setup, operation and applications of a Very Small Radio
Telescope (VSRT) developed by the MIT Haystack Observatory as an education tool to
bring radio astronomy into the classroom. Based on commercially available satellite
television receivers and MIT developed interferometry electronics, the VSRT is a robust
set of equipment for exploring the properties of radio waves, using a low cost, safe and
highly efficient source of radio waves - a compact fluorescent lightbulb (CFL). The
interferometer electronics compare the signal from dual detectors and input the results via
a single USB connector. The software is downloadable from the MIT Haystack
Observatory website and runs on various versions of WindowsTM.
The primary goal of this unit is to study the properties of radio waves and
compare and contrast them with visible light waves. The activities and experiments are
applicable for upper middle school and high school students in the disciplines of general
science, physical science and physics. With many of today’s technological devices
depending on radio waves and their properties, it is useful to expose students to this
invisible portion of the electromagnetic spectrum and allow students to inquire and
explore radio waves.
Some of the activities of this unit concern the transmission and polarization
properties of both visible light waves and invisible radio waves. One activity compares
and contrasts the ability of light and radio waves to transmit through materials such as
water, ice, paper, cardboard, motor oil, plastic and others with some unanticipated results.
Another activity explores the polarized nature of light by testing the polarization of many
visible light sources including lightbulbs, light emitting diodes, digital displays using
LCDs and visible lasers. By studying these phenomena, students are allowed to
experiment and explore these properties of visible light and radio waves.
Experiments geared primarily for high school physics students include studying
the transmission of radio waves through materials of varying thickness and learning about
absorption of waves/radiation in the material. Another experiment in physics is the
quantitative confirmation of the Inverse Square Law, where the power of the radio waves
from the CFL decrease proportionally to the square of the distance between the source
and the detector. An extension of the polarization activity, the Malus Law experiment
allows students to measure the transmission through a pair of polarizers as the orientation
between the polarizers is changed. Also included is the measurement of the wavelength
of the radio waves by Young’s interference method, where the wavelength is nearly 1
inch. Finally, a measurement of the Sun’s angular width is included for physics students
or science club members with advanced mathematical analysis skills.

Additional resources included in this unit are:
1. VSRT Introduction
2. VSRT Assembly Manual
3. VSRT Software Installation Instructions
4. Basic VSRT Operation
5. Series of VSRT Memos
While the experiments listed have been tested with repeatable results, the authors
certainly encourage teachers to develop other activities and experiments to use the VSRT
system. We welcome your feedback and questions regarding this Versatile System for
learning about Radio Telescopes unit.
Stephen Minnigh and Michael Doherty

The following National Science Education Standards Standards and Massachusetts
Science and Technology / Engineering Curriculum Frameworks are addressed either
explicitly or implicitly within the following curriculum module.
The national science educations standards (NSES, 1996) are available at:
http://www.nap.edu/openbook.php?record_id=4962
STANDARD: As a result of activities in grades K-12, all students should develop
understanding and abilities aligned with the following concepts and processes:
Evidence, models, and explanation, Constancy, change, and measurement
As students develop and . . . understand more science concepts and processes, their explanations should
become more sophisticated . . . frequently include a rich scientific knowledge base, evidence of logic,
higher levels of analysis, greater tolerance of criticism and uncertainty.
EVIDENCE, MODELS, AND EXPLANATION Evidence consists of observations and data on which to base
scientific explanations. Using evidence to understand interactions allows individuals to predict changes in
natural and designed systems.
Models are tentative schemes or structures that correspond to real objects, events, or classes of events,
and that have explanatory power. Models help scientists and engineers understand how things work.
Models take many forms, including physical objects, plans, mental constructs, mathematical equations,
and computer simulations.
Scientific explanations incorporate existing scientific knowledge and new evidence
from observations, experiments, or models into internally consistent, logical statements. Different terms,
such as "hypothesis," "model," "law," "principle," ''theory," and "paradigm" are used to describe various
types of scientific explanations. As students develop and as they understand more science concepts and
processes, their explanations should become more sophisticated. That is, their scientific explanations
should more frequently include a rich scientific knowledge base, evidence of logic, higher levels of
analysis, greater tolerance of criticism and uncertainty, and a clearer demonstration of the relationship
between logic, evidence, and current knowledge.
CONSTANCY, CHANGE, AND MEASUREMENT Although most things are in the process of becoming
different—changing—some properties of objects and processes are characterized by constancy, including
the speed of light, the charge of an electron, and the total mass plus energy in the universe. Changes
might occur, for example, in properties of materials, position of objects, motion, and form and function of
systems. Interactions within and among systems result in change. Changes vary in rate, scale, and
pattern, including trends and cycles.
Changes in systems can be quantified. Evidence for interactions and subsequent change and the
formulation of scientific explanations are often clarified through quantitative distinctions—measurement.
Mathematics is essential for accurately measuring change.
Different systems of measurement are used for different purposes. Scientists usually use the metric
system. An important part of measurement is knowing when to use which system. For example, a
meteorologist might use degrees Fahrenheit when reporting the weather to the public, but in writing
scientific reports, the meteorologist would use degrees Celsius.
Scale includes understanding that different characteristics, properties, or relationships within a system
might change as its dimensions are increased or decreased.
Rate involves comparing one measured quantity with another measured quantity, for example, 60 meters
per second. Rate is also a measure of change for a part relative to the whole, for example, change in birth
rate as part of population growth.

As a result of activities in grades 9–12, all students should develop
Abilities necessary to do scientific inquiry
Understandings about scientific inquiry
A critical component of successful scientific inquiry in grades 9-12 includes having students reflect on the
concepts that guide the inquiry. Also important is the prior establishment of an adequate knowledge base
to support the investigation and help develop scientific explanations. The concepts of the world that
students bring to school will shape the way they engage in science investigations, and serve as filters for
their explanations of scientific phenomena. Left unexamined, the limited nature of students' beliefs will
interfere with their ability to develop a deep understanding of science. Thus, in a full inquiry, instructional
strategies such as small-group discussions, labeled drawings, writings, and concept mapping should be
used by the teacher of science to gain information about students' current explanations. Those student
explanations then become a baseline for instruction as teachers help students construct explanations
aligned with scientific knowledge; teachers also help students evaluate their own explanations and those
made by scientists.
Students also need to learn how to analyze evidence and data. The evidence they analyze may be from
their investigations, other students' investigations, or databases. Data manipulation and analysis
strategies need to be modeled by teachers of science and practiced by students. Determining the range of
the data, the mean and mode values of the data, plotting the data, developing mathematical functions
from the data, and looking for anomalous data are all examples of analyses students can perform.
Teachers of science can ask questions, such as ''What explanation did you expect to develop from the
data?" "Were there any surprises in the data?" "How confident do you feel about the accuracy of the
data?" Students should answer questions such as these during full and partial inquiries.
Public discussions of the explanations proposed by students is a form of peer review of investigations, and
peer review is an important aspect of science. Talking with peers about science experiences helps students
develop meaning and understanding. Their conversations clarify the concepts and processes of science,
helping students make sense of the content of science. Teachers of science should engage students in
conversations that focus on questions, such as "How do we know?" "How certain are you of those results?"
"Is there a better way to do the investigation?" "If you had to explain this to someone who knew nothing
about the project, how would you do it?" "Is there an alternative scientific explanation for the one we
proposed?" "Should we do the investigation over?" "Do we need more evidence?" "What are our sources of
experimental error?" "How do you account for an explanation that is different from ours?"
Questions like these make it possible for students to analyze data, develop a richer knowledge base,


reason using science concepts, make connections between evidence and explanations, and recognize
alternative explanations. Ideas should be examined and discussed in class so that other students can
benefit from the feedback. Teachers of science can use the ideas of students in their class, ideas from
other classes, and ideas from texts, databases, or other sources—but
Public discussions of the explanations proposed by students is a form of peer review of investigations, and
peer review is an important aspect of science. Talking with peers about science experiences helps students
develop meaning and understanding. Their conversations clarify the concepts and processes of science,
helping students make sense of the content of science. Teachers of science should engage students in
conversations that focus on questions, such as "How do we know?" "How certain are you of those results?"
"Is there a better way to do the investigation?" "If you had to explain this to someone who knew nothing
about the project, how would you do it?" "Is there an alternative scientific explanation for the one we
proposed?" "Should we do the investigation over?" "Do we need more evidence?" "What are our sources of
experimental error?" "How do you account for an explanation that is different from ours?"
Questions like these make it possible for students to analyze data, develop a richer knowledge base,
reason using science concepts, make connections between evidence and explanations, and recognize
alternative explanations. Ideas should be examined and discussed in class so that other students can
benefit from the feedback. Teachers of science can use the ideas of students in their class, ideas from
other classes, and ideas from texts, databases, or other sources—but
USE TECHNOLOGY AND MATHEMATICS TO IMPROVE INVESTIGATIONS AND COMMUNICATIONS.
A variety of technologies, such as hand tools, measuring instruments, and calculators, should be an
integral component of scientific investigations. The use of computers for the collection, analysis, and
display of data is also a part of this standard. Mathematics plays an essential role in all aspects of an

inquiry. For example, measurement is used for posing questions, formulas are used for developing
explanations, and charts and graphs are used for communicating results.
FORMULATE AND REVISE SCIENTIFIC EXPLANATIONS AND MODELS USING LOGIC AND
EVIDENCE. Student inquiries should culminate in formulating an explanation or model. Models should be
physical, conceptual, and mathematical. In the process of answering the questions, the students should
engage in discussions and arguments that result in the revision of their explanations. These discussions
should be based on scientific knowledge, the use of logic, and evidence from their investigation.
RECOGNIZE AND ANALYZE ALTERNATIVE EXPLANATIONS AND MODELS. This aspect of the
standard emphasizes the critical abilities of analyzing an argument by reviewing current scientific
understanding, weighing the evidence, and examining the logic so as to decide which explanations and
models are best. In other words, although there may be several plausible explanations, they do not all
have equal weight. Students should be able to use scientific criteria to find the preferred explanations.
COMMUNICATE AND DEFEND A SCIENTIFIC ARGUMENT. Students in school science programs should
develop the abilities associated with accurate and effective communication. These include writing and
following procedures, expressing concepts, reviewing information, summarizing data, using language
appropriately, developing diagrams and charts, explaining statistical analysis, speaking clearly and
logically, constructing a reasoned argument, and responding appropriately to critical comments.
UNDERSTANDINGS ABOUT SCIENTIFIC INQUIRY
Scientists usually inquire about how physical, living, or designed systems function.
Conceptual principles and knowledge guide scientific inquiries. Historical and current
scientific knowledge influence the design and interpretation of investigations and the
evaluation of proposed explanations made by other scientists.
Scientists conduct investigations for a wide variety of reasons. For example, they may
wish to discover new aspects of the natural world, explain recently observed
phenomena, or test the conclusions of prior investigations or the predictions of current
theories.
Scientists rely on technology to enhance the gathering and manipulation of data. New
techniques and tools provide new evidence to guide inquiry and new methods to
gather data, thereby contributing to the advance of science. The accuracy and
precision of the data, and therefore the quality of the exploration, depends on the
technology used.
Mathematics is essential in scientific inquiry. Mathematical tools and models guide and
improve the posing of questions, gathering data, constructing explanations and
communicating results.
Scientific explanations must adhere to criteria such as: a proposed explanation must be
logically consistent; it must abide by the rules of evidence; it must be open to
questions and possible modification; and it must be based on historical and current
scientific knowledge.
Results of scientific inquiry—new knowledge and methods—emerge from different types
of investigations and public communication among scientists. In communicating and
defending the results of scientific inquiry, arguments must be logical and demonstrate
connections between natural phenomena, investigations, and the historical body of
scientific knowledge. In addition, the methods and procedures that scientists used to
obtain evidence must be clearly reported to enhance opportunities for further
investigation.
As a result of activities in grades 9-12, all students should develop understanding of
Science as a human endeavor
Nature of scientific knowledge
Historical perspectives
Fundamental concepts and principles that underlie this standard include
SCIENCE AS A HUMAN ENDEAVOR

Inquiry, Experimentation, and Design
in the Classroom
Inquiry-Based Instruction
Engaging students in inquiry-based instruction is one way of developing conceptual
understanding, content knowledge, and scientific skills. Scientific inquiry as a means to
understand the natural and human-made worlds requires the application of content knowledge
through the use of scientific skills. Students should have curricular opportunities to learn about
and understand science and technology/engineering through participatory activities, particularly
laboratory, fieldwork, and design challenges.
Inquiry, experimentation, and design should not be taught or tested as separate, stand-alone
skills. Rather, opportunities for inquiry, experimentation, and design should arise within a
well-planned curriculum. Instruction and assessment should include examples drawn from
life science, physical science, earth and space science, and technology/engineering
standards. Doing so will make clear to students that what is known does not stand separate
from how it is known.

GUIDING PRINCIPLE IX
An effective program in science and technology/engineering gives students
opportunities to collaborate in scientific and technological endeavors and
communicate their ideas.
Scientists and engineers work as members of their professional communities. Ideas are tested,
modified, extended, and reevaluated by those professional communities over time. Thus, the
ability to convey their ideas to others is essential for these advances to occur.
In order to learn how to effectively communicate scientific and technological ideas, students
require practice in making written and oral presentations, fielding questions, responding to
critiques, and developing replies. Students need opportunities to talk about their work in focused
discussions with peers and with those who have more experience and expertise. This
communication can occur informally, in the context of an ongoing student collaboration or online
consultation with a scientist or engineer, or more formally, when a student presents findings
from an individual or group investigation.
Introductory Physics, High School
Learning Standards for a Full First-Year Course
4. Waves
Central Concept: Waves carry energy from place to place without the transfer of matter.
6. Electromagnetic Radiation
Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over
a wide spectrum.
6.1 Recognize that electromagnetic waves are transverse waves and travel at the speed of light
through a vacuum.
6.2 Describe the electromagnetic spectrum in terms of frequency and wavelength, and identify the
locations of radio waves, microwaves, infrared radiation, visible light (red, orange, yellow, green,
blue, indigo, and violet), ultraviolet rays, x-rays, and gamma rays on the spectrum.
II Scientific Inquiry Skills Standard scientific literacy can be achieved as students inquire
about the physical world. The curriculum should include substantial hands-on laboratory and field
experiences, as appropriate, for students to develop and use scientific skills in introductory
physics, along with the inquiry skills listed below.
SIS1. Make observations, raise questions, and formulate hypotheses.
• Observe the world from a scientific perspective.
• Pose questions and form hypotheses based on personal observations, scientific articles,
experiments, and knowledge.
• Read, interpret, and examine the credibility and validity of scientific claims in different sources
of information, such as scientific articles, advertisements, or media stories.
SIS2. Design and conduct scientific investigations.

• Articulate and explain the major concepts being investigated and the purpose of an
investigation.
• Select required materials, equipment, and conditions for conducting an experiment.
• Identify independent and dependent variables.
• Write procedures that are clear and replicable.
• Employ appropriate methods for accurately and consistently
o making observations
o making and recording measurements at appropriate levels of precision
o collecting data or evidence in an organized way
• Properly use instruments, equipment, and materials (e.g., scales, probeware, meter sticks,
microscopes, computers) including set-up, calibration (if required), technique, maintenance, and
storage.
• Follow safety guidelines.
SIS3. Analyze and interpret results of scientific investigations.
• Present relationships between and among variables in appropriate forms.
o Represent data and relationships between and among variables in charts and graphs.
o Use appropriate technology (e.g., graphing software) and other tools.
• Use mathematical operations to analyze and interpret data results.
• Assess the reliability of data and identify reasons for inconsistent results, such as sources of
error or uncontrolled conditions.
• Use results of an experiment to develop a conclusion to an investigation that addresses the initial
questions and supports or refutes the stated hypothesis.
• State questions raised by an experiment that may require further investigation.

VSRT INTRODUCTION
Dr. Martina B. Arndt
Physics Department
Bridgewater State College (MA)
Based on work by
Dr. Alan E.E. Rogers
MIT’s Haystack Observatory (MA)
August, 2009

PREFACE
The Very Small Radio Telescope (VSRT) grew out of an NSF supported project at Haystack
Observatory in Westford, MA. The project was to develop inexpensive and portable radio
astronomy related tools and materials that assist in the teaching of science, engineering,
mathematics, and astronomy in support of the national STEM education goals. The original
target audience was community college faculty and students at Middlesex Community College
(Massachusetts) and Roane State Community College (Tennessee) but the materials are easily
adapted for use in high school and other undergraduate institutions as well.
The basic system is a 2-element interferometer with manual pointing that can be used outside to
make observations of the Sun or inside as a laboratory apparatus for demonstrating the principles
of radio interferometry and basic physics. Students can use the apparatus and accompanying
data analysis to study topics like polarization, reflection, and refraction of microwaves and the
opacity of various materials to radio emission.
This VSRT Instruction Manual is intended to provide an introduction to the theory behind the
VSRT. Detailed instructions on assembling VSRT hardware can be found in the VSRT Assembly
Manual. Directions for installing and running the necessary VSRT software are online at
haystack.mit.edu (VSRT_Team), as are several lesson plans using the VSRT.

INTRODUCTION TO INTERFEROMETRY
Most radio telescopes you have probably seen involve one curved reflective surface that collects
light from a distant source. The larger the reflective surface, the more light you can collect, and
the fainter the objects you can see. As the wavelength you are interested in gets larger and larger
(remember, radio wavelengths range from centimeters to
kilometers), you need to make your reflective surface
larger and larger if you want to see any details of the
object you are observing. Unfortunately, technology
limits how large we can make these reflective surfaces –
think of the weight alone of a really large radio telescope.
One of the largest single dish radio telescopes, Arecibo
in Puerto Rico – with a diameter of about 300 meters – is
built into the ground and can only observe sources to
within 20 degrees of straight up. (Figure 1: Arecibo
Observatory )

One way to increase the light gathering power of a radio
telescope is to connect more than one reflecting surface
together to act as an interferometer. The Very Large Array
(VLA) in New Mexico (Figure 2) is an interferometer made
up of 27 telescopes, each with a diameter of 25 m. When used
together, the VLA dishes can see detail as though it were a
single dish with a diameter of 36 km. (VLA, Wiki)
Radio astronomers are used to combining signals from more
than one antenna to obtain data from radio sources. The
VSRT is an example of an instrument that combines signals
by adding them; therefore, it is useful to understand how we
combine signals from multiple telescopes observing the same
object at the same time.