dec 08 02 radio telescope dane coffey, charles wakefield, stephanie kaufman, seung hyun song
TRANSCRIPT
DEC 08 02RADIO TELESCOPE
Dane Coffey, Charles Wakefield, Stephanie Kaufman, Seung Hyun Song
Project Introduction and GoalDesign 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 ObservatorySponsored by the SSCL
Terminology
Celestial Coordinate SystemHorizontal Coordinate SystemRight Ascension and DeclinationAzimuth and Elevation
Concept Sketch
Parabolic Dish
Subreflector
Feedhorn
Coaxial Switch
Noise Source
Low Noise Amplifier
RF Mixer
Receiver
Limit Switches
Motors
Computer
Potentiometers
Stub Tuner
Motor Control
Attenuator
Web Server
Motor Control Interface
Attenuator Control
Coaxial Switch Control
User Interface Software
Internal Software
Limit Switch Detection
DAQ Card
Radio Source
Radio Waves
Coaxial Cable
Serial Cable
Outside Inside
Initial Situation
Ongoing since 1999Dish itself is assembled and motor’s are
functioningFail safe limit switches are installed and
functionReceiving system was purchased and
installedBasic software had been written
Software interface for controlling movement
Tracking software Raster Scan software
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
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
Deliverables
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.
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.
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.
Non-functional Requirements
OverallNFR002: 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.
CurrentNFR007: The impedance of the feed horn shall
be matched with the rest of the system as accurately as possible.
Operating Environment
Telescope outside at FickComponents indoors connected to
telescope~54 ° F indoors when not occupiedSoftware is written in LabVIEW and runs
on a Windows PCOutside temperatures from -20 ° F – 110
° FExposed to strong wind, rain, and snow
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
Design and Implementation
Impedance Match
Attenuator Control
Successive Raster Scan
Unified User Interface
Pointing Correction
Signal Generator
Parabolic Dish
Subreflector
Feedhorn
Coaxial Switch
Noise Source
Low Noise Amplifier
RF Mixer
Receiver
Limit Switches
Motors
Computer
Potentiometers
Stub Tuner
Motor Control
Attenuator
Web Server
Motor Control Interface
Attenuator Control
Coaxial Switch Control
User Interface Software
Internal Software
Limit Switch Detection
DAQ Card
Radio Source
Radio Waves
Coaxial Cable
Serial Cable
Outside Inside
Impedance Matching
System is 50 Ohm Feedhorn is 19.5 +
j19.7 at 1420 MHz Approximately 25% is
lost
Impedance Matching
Single stub designMicrostrip etched on copper clad glass epoxy
boardFeedhorn impedance measured at FickAssistance from Dr. Robert Weber
Impedance Matching
Tested using a model of the feedhornReturn loss is -30 dB at 1420 MHzMounted in Watertight Enclosure
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.
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
Attenuator Testing
Showed hysteresis characteristic Turn-on voltage: 8.5V Turn-off voltage: 3V
Insertion loss at 70MHz 0.6dB (65.3mV/70mV)
Attenuator Control
Eagle Schematic
Attenuator Control PCB Layout
Attenuator Control Testing Result
Attenuator Control Changes in DesignAddition 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
Attenuator Control Considered DesignsOptocouplerOpen Collector Buffer
Attenuator Control Board
Raster Scan User Interface
Raster Scan Inputs
Raster Scan Outputs
Raster Scan Design/Implementation
Dish moves to Right Ascension and
Declination Coordinate
Intensity is read the number of times specified (making sure that the dish is in the correct place) by user and then averaged.
User Specifies:- Start and Stop Right Ascension- Start and Stop Declination- Right Ascension and Declination Step- Amount of Noise Reduction
Is there another
coordinate?
Graph of intensities is displayed and
output file is written.No
Yes
Raster Scan Testing
Noise Reduction = 1 Noise Reduction = 5
Maximum Intensity: 178Minimum Intensity: 143Difference: 35
Maximum Intensity: 158Minimum Intensity: 137Difference: 21
Pointing Correction and CalibrationTwo 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
Pointing Correction SoftwareReads 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 fileDesign: Scan
1 direction at a time Gaussian Fit Greedy Scheduling
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 betweenProblems
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?
Elevation Min Elevation Max Azimuth Min Azimuth Max-13.76208 83.58955 -41.15904 348.617172
Pointing Calibration
Motors swept at constant speed Obtained piecewise linear functions by combining with
previous results
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
Unified User Interface
Single application to encompass all functionality for basic radio astronomy
Four sections were identified
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
Real-time update – Telescopes current status is continually polled
Telescope power - A single switch to turn on all components of the system
Unified User Interface
Automatic control – scheduler interface, outputs last scan results
Care was taken to ensure optimal interface for performing scans
Unified User Interface
Manual control – perform scans on the fly or position manually
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
Signal Generator
Two outputs: 70 MHz 1420 MHz
Switch only allows operation of one output at a time
PortableOperates on two 9-
volt batteries
Signal Generator
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
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
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
Cost Analysis
Budgeted Cost Scheduled (@ $10.00/hr)
Budgeted Cost Performance (@ $10.00/hr)
Actual Cost Performance (@ $10.00/hr)
Cost Variance
Schedule Variance
$8,800 $7,952 $8,485 0.94 .90Overall 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
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
Acknowledgements
Our Advisor Dr. Basart The SSCL and Matt Nelson Dr. Weber
Questions?