DEC 08 02 RADIO TELESCOPE

1. DEC 08 02RADIO TELESCOPE Dane Coffey, Charles Wakefield, Stephanie Kaufman, Seung Hyun Song

2. Project Introduction and Goal • Design and develop a working Radio Telescope that operates at the 1420 MHz frequency. • This is needed to give Astronomy and Physics students and faculty the ability to perform radio astronomy at Iowa State University • Telescope located at Fick Observatory • Sponsored by the SSCL

3. Terminology • Celestial Coordinate System • Horizontal Coordinate System • Right Ascension and Declination • Azimuth and Elevation

4. Concept Sketch

6. Initial Situation • Ongoing since 1999 • Dish itself is assembled and motor’s are functioning • Fail safe limit switches are installed and function • Receiving system was purchased and installed • Basic software had been written • Software interface for controlling movement • Tracking software • Raster Scan software

7. Initial Problems • Basic existing software is scattered and not cohesive • Position system is too inaccurate to even hit the sun • There is a lot of noise in the signal when performing raster scans • An attenuator was purchased but not functioning • The feed horn impendence is not matched • Debugging the receiver and front end is difficult

8. Initial Need • Create a single user interface with all critical software components • Create fully automatic position correction software and calibrate the current system • Improve S/N ratio by doing successive raster scans • Design attenuator control and develop software to control it • Design a single stub tuner to match the impedance • Create a simple two frequency signal generator for easy debugging of the system

9. Component Description Unified user interface software The unified software will be a LabVIEW program for users to easily interface with the telescope. Pointing correction software This LabVIEW software will be used to calibrate the telescope and generate offsets for more accurate telescope pointing. Raster Scan Software The raster scan software will modified to do successive scans; this will be used to reduce the amount of noise in the image. Feed Horn Circuitry Circuitry will be added to the feed horn to impedance match it with the coaxial cable. Functioning Attenuator The attenuator will be installed and software will be modified to allow control the attenuator. Signal Generator A two frequency signal generator will be created to easily debug the receiver and the front end. Deliverables

10. Functional Requirements Overall • FR001: The system shall be capable of receiving, amplifying, filtering, and capturing the intensity of incoming radio signals at a frequency of 1420 MHz. Current • FR008: The system shall have a single unified user interface which incorporates all of the critical aspects needed for dish control and data collection including raster scan, manual control, tracking and intensity output features. • FR011: The unified software shall have a scheduler interface for users to set up complex daily data collection schedules.

11. Functional Requirements Current Cont. • FR017: The system shall have pointing correction calibration software to automatically determine the offsets for elevation and azimuth. • FR018: The pointing correction software shall determine the offsets by scanning near known radio source locations. • FR022: The raster scan software shall perform successive scans to decrease the noise in the image. • FR024: The attenuator shall be capable of attenuating saturated signals with controllable gain of 0 to 15 dB.

12. Non-functional Requirements Overall • NFR002: The system software interface shall be intuitive, and user friendly. • NFR006: The positioning of the telescope shall have an accuracy of within one-tenth of a degree. Current • NFR007: The impedance of the feed horn shall be matched with the rest of the system as accurately as possible.

13. Operating Environment • Telescope outside at Fick • Components indoors connected to telescope • ~54 ° F indoors when not occupied • Software is written in LabVIEW and runs on a Windows PC • Outside temperatures from -20 ° F – 110 ° F • Exposed to strong wind, rain, and snow

14. Risks and Risk Management • Weather – Take advantage of nice weather • Unforeseen problems – Be familiar with entire system • Knowledge passing – New teams need to involved as much as possible due to the large nature of the system

15. Design and Implementation • Impedance Match • Attenuator Control • Successive Raster Scan • Unified User Interface • Pointing Correction • Signal Generator

16. Impedance Matching • System is 50 Ohm • Feedhorn is 19.5 + j19.7 at 1420 MHz • Approximately 25% is lost

17. Impedance Matching • Single stub design • Microstrip etched on copper clad glass epoxy board • Feedhorn impedance measured at Fick • Assistance from Dr. Robert Weber

18. Impedance Matching • Tested using a model of the feedhorn • Return loss is -30 dB at 1420 MHz • Mounted in Watertight Enclosure

19. Purpose of Attenuator • In the Spring of 06, the team was experiencing signal saturation when observing the Sun • In Fall of 06, the team bought the attenuator, JFW 15P-1499.

20. Purpose of Control Circuit • To match the voltage and current level • Daq card digital I/O provide 0V low, 5V high • Attenuator requires 0V low, 12V high • Daq card has a very low current limit • Attenuator requires 15mA of current for the relay to switch

21. Attenuator Testing • Showed hysteresis characteristic • Turn-on voltage: 8.5V • Turn-off voltage: 3V • Insertion loss at 70MHz • 0.6dB (65.3mV/70mV)‏

22. Attenuator Control Eagle Schematic

23. Attenuator Control PCB Layout

24. Attenuator Control Testing Result

25. Attenuator Control Changes in Design • Addition of a buffer • To provide more current cushion • 45mA from 25mA • Change from quad op amp to quad comparator • To solve the voltage drop-off problem • Output voltage increased from 9.5V to 12V

26. Attenuator Control Considered Designs • Optocoupler • Open Collector Buffer

27. Attenuator Control Board

28. Raster Scan User Interface

29. Raster Scan Inputs

30. Raster Scan Outputs

31. Raster Scan Design/Implementation User Specifies: - Start and Stop Right Ascension - Start and Stop Declination - Right Ascension and Declination Step - Amount of Noise Reduction Dish moves to Right Ascension and Declination Coordinate Yes Intensity is read the number of times specified (making sure that the dish is in the correct place) by user and then averaged. Is there another coordinate? Graph of intensities is displayed and output file is written. No

32. Raster Scan Testing Noise Reduction = 1 Noise Reduction = 5 Maximum Intensity: 178 Minimum Intensity: 143 Difference: 35 Maximum Intensity: 158 Minimum Intensity: 137 Difference: 21

33. Pointing Correction and Calibration • Two parts: • Software to automatically determine the minute offsets in the pointing to use for future measurements • Calibrating the current pointing system so that known sources can actually be hit • The software relies on the assumption that known sources can be hit

34. Pointing Correction Software • Reads in a known source catalog and breaks up the visible region into a grid scanning sources in each grid in both azimuth and elevation direction • Outputs offsets to text file • Design: Scan • 1 direction at a time • Gaussian Fit • Greedy Scheduling

35. Pointing Calibration • Feedback values are obtained by potentiometers attached to motors • Current algorithm and calibration method: • Azimuth limits switches are assumed at 0 and 360 degs • Elevation limits switches are assumed at 0 and 90 degs • Linear fit between • Problems

36. Elevation Min Elevation Max Azimuth Min Azimuth Max -13.76208 83.58955 -41.15904 348.617172 Pointing Calibration • Similar process – scans of sun were taken, date/time and current feedback were recorded • Extrapolated limit switch locations • Does not pass sanity check • Potentiometers are not linear enough?

37. Pointing Calibration • Motors swept at constant speed • Obtained piecewise linear functions by combining with previous results

38. Pointing Calibration • Problems • Values change a lot with temperature outside • Conclusion • Accurate enough to hit the very large sun • Current system is inadequate to hit any other source • Replace with digital shaft angle encoders

39. Area Purpose Real-Time Update A section of controls that continually polls the telescope to give real-time status updates. This includes current intensity, location in both celestial and horizontal systems, and limit switch status. Telescope Power A single switch to turn the telescope on or off remotely. Automatic Control Functionality that allows for the setting up of automatic scans of sources using a scheduler interface for time in the future. Manual Control Functionality that allows for immediate movement of the telescope and immediate scans of sources. Unified User Interface • Single application to encompass all functionality for basic radio astronomy • Four sections were identified

40. Unified User Interface • Real-time update – Telescopes current status is continually polled • Telescope power - A single switch to turn on all components of the system

41. Unified User Interface • Automatic control – scheduler interface, outputs last scan results • Care was taken to ensure optimal interface for performing scans

42. Unified User Interface • Manual control – perform scans on the fly or position manually

43. Unified User Interface • Status: • All functionality is implemented and tested • Telescope power doesn’t function because of a hardware issue that is being addressed by the new team • With a combination of our user interface and pointing calibration, blind scans of the sun can be performed easily, which has never been done before

44. Signal Generator • Two outputs: • 70 MHz • 1420 MHz • Switch only allows operation of one output at a time • Portable • Operates on two 9-volt batteries

45. Signal Generator

46. Signal Generator • Both outputs have been tested • 70 Mhz signal stable when input is at least 13.5V • 1420 MHz signal stable when input is at least 16V • 1420 MHz signal is acceptable when input is at least 15.5V

47. End of Semester Status and Future • Issues were identified with the hardware that turns the hardware components of the system on and off remotely • We’ve worked with the new team to fix this and they will be installing the new board • Once the potentiometers are replaced and the new system is calibrated the telescope will be ready for basic use with our new software • The same process and software used in calibration can be repeated to calibrate the shaft angle encoders • Mechanical problem with the shaft that rotates the azimuth potentiometer

48. Lessons Learned • A large system such as this requires frequent checks and maintenance that is hard to provide from senior design students • Not having immediate access to the system is a huge limitation • Minor setbacks dominate our time at the observatory • Documentation needs to be kept up to date with so many teams switching in and out

49. Cost Analysis • Overall ended up slightly over budget, some things went quicker, others longer • Slightly below on scheduling, due to a few loose ends • There was quite a bit of variance in some of the actual/planned hours, but it averaged out

50. Conclusion • We accomplished all of the tasks we set out to do at the beginning of the project • Many of the topics covered were unfamiliar at the beginning of the semester, it was a great learning experience • The positioning is the one thing preventing the telescope from being used practically • Barring any major setbacks, we should be able to get astronomy students involved and using the telescope next semester