Information in Radio Waves

Transcription

1 Inquiry Project: Investigating Radio Signals with Software defined Radio (SDR) Signal Defined Radio (SDR) is a technology that enables users to capture radio transmissions and decode them using only software instead of the physical components of a traditional radio system. This is done by encoding the signal processing components as programs and incorporating them onto a processor chip. The benefit for this technology is that it will enable greater flexibility and adaptability for devices that use radio communication. Instead of having a hardware system that conforms to a single set of standards and protocols for sending or receiving signals, the software can be programed to use a multitude of standards and protocols. As systems and technologies develop in the future, the software systems have only to be updated or re- programed to accommodate the new developments. Applications include machine to machine communications and robotics. In this activity you will use an SDR receiver to investigate the radio transmissions around us. Project Requirements Part 1: Exploring local Radio (formative) Explore the physics of radio through FM transmission Product: Analysis questions Part 2: Observation of basic signal properties (formative) Observations of the characteristics of the signal as observed at the receiver. Product: recordings Part 3: Analysis of Signals (formative) results are presented in graphical display Part 4: Report on investigations with the FM transmitter Final product can be a written report, a blog, a presentation, or Scoring rubric (appendix c) linked to NGSS Standards assessed: Communicate technical information about how some technological devices use the HS- PS4-5 principles of wave behavior and wave interactions with matter to transmit and capture information and energy. Utilize a device that works within given constraints to convert one form of energy into HS- PS3-3 another form of energy. RET

2 SDR Project Investigation 1: Tune in to a local FM station (Near Boston find 99.5 WCRB Classical New England) When you are tuning your SDR to a frequency, you are simply adjusting the window within which the software is processing and outputting data for audio (listening). The two visual displays will allow you to visualize the signal that is being intercepted by the antenna. Procedure: Follow the set up procedures for both the RTL receiver and the SDR# software in Appendix 1 and 2. Plug in the USB stick and attach the antenna Start SDR# Tune the radio to a frequency of 99.5 MHz Introductory analysis and questions: There are many features to this software interface that are highly technical with respect to the signal processing and analysis of radio signals. You will only be using a few of them in this activity In the top view you see an x- y line graph that is continuously updated (hence the noisy look). What are the units on the x- axis? What are the units on the y- axis? In the FFT Display plugin, select the IF spectrum and the audio spectrum. What is the width of the IF spectrum band in frequencies? Once you have the peak set up, take the db value of the baseline and the top of the peak. Find the difference to get a pseudo- power estimate. This is how much power is being collected by our antenna. Record your answer below. RET

3 Investigation 2: What are those crazy db units? In radio science we often are dealing with quantities that have very wide ranges such as factors of one thousand to millions. Representing numbers that have such a high range can be difficult. The unit db is used to show the power of 10 differences in quantities. 1 db is simple 10 1, 0.1 db = On the screenshot you will see a spectrum (with a lot of Radio frequency interference, RFI) of a local radio station 99.5 WCRB near Boston MA. Notice the y- axis of the plot, it goes from 0 at the top to - 40 or so where it joins the x- axis. Which is a higher actual value - 10 db or - 40 db? Now you will learn some factors in how the power output from the transmitter station is received and why we are getting the numbers that we are getting. Part 1: Where are we relative to the station? You can find the distance between your location and the transmitting station by plugging in the latitude and longitude for both into an online calculator. The calculator uses some interesting geometric properties to find the distance from one point on a sphere to another, of course assuming the earth is a sphere. I recommend this caluculator, and- azimuths- between- two- sets- coordinates First, gather some information about your radio station: Station carrier frequency MHz Height above ground ERP (Estimated Radiative Power) Transmitting station Your location Latitude longitude Distance in meters The key quantities from the data you have collected are the ERP, how much power is being emitted by the transmitter, and the distance from the source, D. RET

4 Part 2: The inverse- square law for radiative power Estimating the received power using the irradiance invariance law, the energy from the station must be conserved, so as it extends in all directions it spreads out over a larger area and is decreased for that reason. The illustration to the left shows the inverse square relationship between Intensity and the radius of the imaginary sphere extending out from the source. In our case the ERP is the source strength And the power density, p, is the source strength where D is our distance between our location and the transmitter. p = ERP 4πrD! The power at the receiver is then: P! = pa! Where p r is the power received by the receiver antenna, p is the power density from the transmitter, and A r is the surface area of the receiver antenna. Use the values that you found for the ERP and the Distance, calculate the power density from the transmitter and the power at the receiver in the space below. Rewrite the equations with our values substituted in and show your calculations with correct units. This is an increadibly idealized situation. Take a look at some of the assumptions that are made: it assumes that the radiation is emitted equally in all directions, isotropically, which NEVER happens with antennae. It also assums that there is no interference with the ground, water dropplets, etc It also assumes that every surface of the antenna will collect radiation equally, which doesn t happen in reality. Given all of those assumptions, explain how your theoretical db value compares with what is being recorded and what you think is causing the difference if there is any? RET

5 SDR Project Part 3: Basic signal observations. Set up the receiver and SDR# software in the same configuration as for investigation 1 and tuned to 99.5 MHz WCRB. 1. Measure how wide the peak is by rolling the mouse over either edge of the peak a. Left edge = b. Right edge= c. Difference= 2. The FCC sells licenses for broadcast in the FM radio band as 200 KHz channels. Is the broadcast you are listening to using all of the allotted bandwidth? If not, explain why you think they might not be. 3. Expand the Audio Spectrum display so that you can see it while you are monitoring the signal view. Describe the behavior of the signal in Db and from the Audio Spectrum display as the music is playing. How does volume change the shape? How do different sounds appear to change the shape? Use the waterfall view to illustrate your descriptions. RET

6 4. Describe the peak and the spectrum from the Audio Spectrum view and sketch them in the space provided. To sketch you might pause the radio for a moment when silence or full music are happening. a. When there is silence on the station Description: IF Spectrum: Audio spectrum view b. What does the peak look like when there is a full period of music? Description: IF Spectrum: Audio Spectrum Now explore other stations and compare the strength, the type of spectra, Where the station is located. Extension activities: 5. Do you see two smaller peaks on either side of the main peak? If so this means that the station is broadcasting in stereo. Research stereo transmissions 6. Do you see two rectangular signals on either side of the main peak? If so, this means the station is broadcasting in HD which is a digital broadcast. Find out what type of information those flat signals might be carrying. RET

7 SDR Project Part 4: Investigations with a local FM transmitter. For this activity you will need an FM transmitter like the ones that can be used to broadcast an IPOD signal to the radio in your car. I recommend this one at amazon ( F8&psc=1) Procedure Get each team of 2 or 3 set up on SDR# and ready to scan for FM stations One person or team will be the hider. Using any device that plays music and that has a headphone jack, They must find a song, a voice recording, or a phone conversation that they would like to broadcast to the class. With the FM transmitter they will select a frequency to broadcast on. This must be a frequency that is not to close to any other stations broadcast in a region of the spectrum where there is just static. The other groups in the room will try to find that person s broadcast as quickly as possible. Once someone has found the broadcast the hider can move the frequency around by.1 MHz to demonstrate the change in transmission channel. Here are some research questions that could be used to develop some experiments with your groups: What is the range of the transmitter? What objects or materials will interfere with the signal? How does the volume affect the spectrum of frequencies received by the tuner? Other student generated questions. Design your own experiment to answer one of these questions. Be sure to make a hypothesis/prediction in If, then, because format. Upon teacher approval, carry out your investigation according to your class s protocols for safety and accuracy of measurement. Collect data and illustrate it graphically Write a report for this experiment using the rough draft template found in appendix D RET

8 References sdr.com/rtl- sdr- quick- start- guide/\ for- using- sdr/ astr.gsu.edu/hbase/forces/isq.html websdr.no- ip.org:8901/ RET

9 Appendix A : SDR# SoftwareSetup These instructions are adapted from the blog I followed the automated install instructions for windows: Go to and download the file sdr- install.zip Extract the folder and navigate to the sdr- install folder Double click on the install file this is a batch file that will set up all the required prorams The RTL- SDR device driver needs to be installed with Zadig Running Zadig o This part can be a little different depending on your OS and hardware. o Open Zadig and allow the program to make changes to your computer if asked. o Under the options menu select list all devices o o Select the Bulk in interface 0 option Click install driver Once the the WinUSB driver is installed you are ready to run SDR# with the RTL- SDR/USB input device. Find the sdrsharp folder in the newly extracted sdr- install Double clickon the sdrsharp.exe file with the icon RET

10 Device set up Under the source menu select the RTL- SDR/USB Click the gear icon and set the sampling rate to and select the Tuner AGC setting Now click the play button and tune in to a local FM station. RET

11 Appendix B: SDR Project Scoring Rubric: To be handed in with final project. Communicate Principles of EM waves Energy of the system 4 includes all criteria from P plus: Fundamental principles are used to evaluate the results of an original investigation. Principles are used to inform the design of an experiment to test predicted values of properties of radio waves. Experimental results are formulated to make predictions about energy requirements or losses in the system with emphasis on communication closure. 3 includes all criteria from BP plus: Fundamental principles are applied to a line of inquiry where original data is collected and cited in the report. External resources are used to support discussion. Principles of waves are tested with original observations of radio waves from local resources. Observations are analyzed and compared with theoretical values. Energy conversion is examined including inputs and outputs of energy from the system of radio communications with specific examples from the SDR observations. 2 includes all criteria from LP plus: Fundamental principles are demonstrated by descriptions of observations made with the SDR device. Shows the uses of radio waves through observations of a variety of sources. Energy conversion is illustrated using observations of radio waves. 1 Rough draft is completed and revised for final product. Fundamental principles are stated but are not related to observations. Describe the basic properties of waves that can be used to communicate information. Basic description of conversion of sound energy to electromagnetic radiant energy and vice versa. Teacher comments: RET

12 Appendix D General Lab Report Rough Draft Template Communicating results of an experiment is an important step in the science process. The following format is derived from standard peer reviewed research journal articles. Follow the guidelines closely. General Considerations: Each section should be in paragraph format. Write in the passive voice. Do not use personal pronouns like I, we, he, she, they, our, etc. Do not use the words it or thing. This will add clarity to your writing. Every section of the lab should have a header. Each person must have their own lab report, written in their own words. YOU MUST CITE ALL OF YOUR RESEARCH SOURCES using in-text citations and include the full citation at the end of the report in a References section. It must be typed via Google Docs to get credit for use of class time and to receive teacher feedback. The final report should be submitted to your teacher through the Turn It In website (turnitin.com). Components: 1. Title - Your name, class block, and date in the upper right hand corner. A descriptive title (not Science Lab Report ) should be located in the center of the paper before the introduction. Your Name: Class Block: Date: Lab Title: RET

13 2. Introduction Introductory paragraphs are meant to summarize the background information related to the experiment you are conducting, providing the motivation for your work and putting it into a broader scientific context (outside references may be used). You will need to state the purpose, objective and/or research question of the study in this section. If appropriate, the research question is followed with the experimental hypothesis. Do not summarize the experiment in the introduction this will occur later in the lab report. Exceeding (E) Meeting (M) In-progress (IP) Limited Progress (LP) Introduction with Background research Includes all criteria in Meeting plus Background providing depth and detail. Introduction sets the context of the experiment with reference to theories and research. Includes all criteria in IP plus Clearly states the purpose of the paper as it relates to the class learning objectives or topic. The research question is stated in a testable way. The hypotheses because is reasonable based on general knowledge and observations. Includes all criteria in LP plus Purpose, research question, and hypotheses are stated. Hypotheses are in if then because... format. Introduction states the purpose, research question or hypothesis of the experiment. Introduction: RET

14 3. Methods Written in past tense. Summarize the experimental design numbers of trials, types of data collected. (For some experiments this requires a description of the independent variable, dependent variable, constants, and any controls that were used). Describe the basic procedure including the tools that were used to complete the study/experiment. This should not be a bulleted list of steps (only appropriate for chemistry). Only include tools or materials that were specific to this experiment. You do not need to say such basic things as, a metric ruler was used to measure the change in length ; all scientists know which tools are appropriate for measuring length. You should also include a description of the data analysis performed if this is applicable, i.e. data from each trial was averaged, or collected data was compared with data from a control. It should flow and be succinct. Exceeding (E) Meeting (M) In-progress (IP) Limited Progress (LP) Methods Includes all criteria in Meeting plus Includes all criteria in IP plus Includes all criteria in LP plus Methods are listed. Procedures are summarized with the goal of making the results understandable for the reader. Experimental design is detailed stating the independent and dependent variables, constants, controls, and how a high degree of accuracy is to be achieved. All methods are summarized with mention of measured variables and number of trials Methods: RET

15 4. Results The results section contains two subsections: Data and Analysis Data - State the observations and data obtained in the lab. In this section you can use data tables, graphs and lists to convey your data. This section can include both qualitative and quantitative data. Tables and charts should be accurate, organized and include clearly labeled column names and SI units of measurement. Each graph or data table must have a descriptive title and number (i.e. Table 1: Data collected in a closed system, Graph 2: Change in mass of a chemical reaction over time). Exceeding (E) Meeting (M) In-progress (IP) Limited Progress (LP) Results: Data Includes all criteria in Meeting plus Estimates of accuracy and error are reported. Includes all criteria in IP plus Tables, charts, and graphs include appropriate labels and titles. Presentation done neatly with no errors. Includes all criteria in LP plus Tables, charts, and graphs are used to illustrate basic trends in the data. Primary results are reported. Practice sketches of Graphs, Tables, Diagrams, Charts, etc below RET

16 Analysis - In the analysis you should state any general trends or patterns that are present in the data, including any values that seem unexpected or highly different from the other values. You should only state the facts, do not make conclusions. Refer to your data table or graph using one of two formats: Graph 2 shows OR. (Graph 2). Exceeding (E) Meeting (M) In-progress (IP) Limited Progress (LP) Results: Analysis Includes all criteria in Meeting plus Further analysis is carried out where appropriate in order to test trends and relationships Includes all criteria in IP plus References to tables, charts or graphs using the appropriate format - Graph 1 shows or...(graph 1). Trends are discussed in terms of the relationship between variables. Includes all criteria in LP plus Data is described in paragraph form including maximums, minimums, and overall trends/comparisons. The key results are stated. Analysis: RET

17 5. Discussion & Conclusions - In paragraph form restate the purpose/objective/research question of the lab and any hypotheses that you were testing. Provide clear statements about how your data supports or does not support your objective/hypothesis. The more specifics the better. You should be referencing back to your class lessons to help you make connections between the data and WHAT the data means. If instructed directly by your teacher put your work into broader context, how do your research results relate to the larger world (use references)? Next you should state what problems may have occurred and what changes might be helpful in clarifying your results. Was there any introduction of error? If so what caused the error. Human error is not an appropriate description of the error you need to be specific. To be Exceeding in any class: You need to complete all other parts of the discussion and include any changes to your experiment that might be helpful in clarifying your results. Come up with a new but related testable research question that would help further your understanding of the topic. Exceeding (E) Meeting (M) In-progress (IP) Limited Progress (LP) Conclusio n/ Discussion Includes all criteria in Meeting plus Suggests a related testable research question is provided. Strengths and limitations (errors) and makes valid suggestions on how to reduce the error. Includes all criteria in IP plus Connection back to hypotheses is correct based on the results. Relationship between variables is discussed, patterns are logically explained. Results are connected back to and integrated with the learning objectives or topics of study from class. Includes all criteria in LP plus Original research question and hypotheses are presented. Results are discussed in terms of supporting or not supporting the hypotheses. Results are discussed in relation to the original purpose or question. Discussion RET

18 6. References This section should have a complete list of citations for any resources or references you used in the writing of your final report. (See the attached sheet and/or Use Easy Bib.) RET

19 Book Sample References MLA Citation Style Okuda, Michael, and Denise Okuda. Star Trek Chronology: The History of the Future. New York: Pocket, Journal Article Wilcox, Rhonda V. "Shifting Roles and Synthetic Women in Star Trek: The Next Generation." Studies in Popular Culture 13.2 (1991): Newspaper or Magazine Article Di Rado, Alicia. "Trekking through College: Classes Explore Modern Society Using the World of Star Trek." Los Angeles Times 15 Mar. 1995: A3. Book Article or Chapter James, Nancy E. "Two Sides of Paradise: The Eden Myth According to Kirk and Spock." Spectrum of the Fantastic. Ed. Donald Palumbo. Westport: Greenwood, Junipero Serra High School Dr. Senegar-Mitchell Website Lynch, Tim. "DSN Trials and Tribble-ations Review." Psi Phi: Bradley's Science Fiction Club Bradley University. 8 Oct < RET