1. 8/23/2015Website - dmradas.co.uk1 Radio Astronomy David Morgan

2. 8/23/2015Website - dmradas.co.uk2 Radio Astronomy - part 1 Introduction Historical discoveries Basic Telescope Requirements Receivers, Antennas, sensitivity Observing Frequencies Common observation bands, noise levels What we are going to build What we are going to measure Mk1 at Jodrell Bank Radio Window

3. 8/23/2015Website - dmradas.co.uk3 Radio Astronomy Introduction Why do Radio Astronomy ? Observe phenomena you can’t see Discover new Astronomical objects - pulsars, quasars etc Uncover new physics processes – eg H Line & synchrotron emission Complements Optical Astronomy – optical identification is crucial Radio Astronomy has opened our mind about the universe Hydrogen distribution in Milky Way spiral arms The existence of Pulsars – Neutron Stars – Super dense matter Discovery of distant Quasars – formed early in the universe Complex molecules in interstellar space Confirmation of Big Bang – 3 0 K Microwave Background Cosmic Microwave Background Combined optical & Radio

4. 8/23/2015Website - dmradas.co.uk4 Radio Astronomy - Beginnings Karl Jansky 1931 20MHz Bell Labs accidental discovery of cosmic radio signals Grote Reber 1937 160 & 480MHz

5. 8/23/2015Website - dmradas.co.uk5 Radio Astronomy My early attempts at Radio Astronomy at school 15 foot dia. Antenna skeletonMeMr Wilkins Receiver – made from bits of TV sets

6. 8/23/2015Website - dmradas.co.uk6 Large Telescopes Jodrell Bank Radio telescopes Central Mast Mk 1 The Feed

7. 8/23/2015Website - dmradas.co.uk7 Radio Astronomy My 3m dia dish with 1.4GHz Feed f/D=0.28 beamwidth = 5 0 Gain = 30dB or 1000 times Frequency in MHz = 300 / Wavelength in metres

8. 8/23/2015Website - dmradas.co.uk8 Radio Astronomy Natural Ambient Radio Noise - Low Noise region Antenna Temperature 0 K (noise level) Wavelength Radio noise power can be expressed as an equivalent temperature P = K TB P = noise power K= Boltzmans Const. T = Temperature 0 K B = bandwidth

9. 8/23/2015Website - dmradas.co.uk9 Radio Astronomy G dir G ref S Source S atmos S EM I Man Ground Temp = T G 0 K Low Noise Amp Noise AMP P out P out =  S s +S a +S EM +I M +(G d +G r ) + N AMP Depends on T G Total Power Receiving System - Signal Contributions All noise sources ‘in grey’ must be stable to better than 0.1dB Feed Reflector

10. 8/23/2015Website - dmradas.co.uk10 Radio Astronomy 408MHz feed/ 3m Dish 1420MHz feed/ 3m Dish 408MHz Twin Yagi LO Synthesised Receiver Signal Processing & Test Equipment PC A to D converter + Software packages Output Data Amateur Radio Telescope System Cooled Head Amplifier Cooled Head Amplifier Cooled Head Amplifier

11. 8/23/2015Website - dmradas.co.uk11 What are we going to Build ? 1m diameter offset dish working at 11 GHz Build part of the receiver and make a map of the sky at 11 GHz Observe the radio emission from the SUN, moon, satellites Also measure microwave signals from trees, ground, buildings, people

12. 8/23/2015Website - dmradas.co.uk12 Receiving System The receiver has 6 main components Dish Feed / low noise receiver (LNB) Detector Post detector amplifier Digitiser Computer Detector Post detector amplifier Digitiser

13. 8/23/2015Website - dmradas.co.uk13 Actual components Examples of system components Receiver Detector Post detection Amplifier

14. 8/23/2015Website - dmradas.co.uk14Challenges Mechanical Obtain tripod Design elevation mechanism Make elevation mechanism Design and make electronics box Electronic Understand what needs to constructed Become familiar with components and circuit Practice soldering Mark out Circuit Board Place components Solder in place Test circuit

15. 8/23/2015Website - dmradas.co.uk15 The amplifier

16. 8/23/2015Website - dmradas.co.uk16 Observing the SUN Because the Sun is hot it emits light and radio waves The hotter something is the more it radiates It radiates best at high frequencies 11 GHz is a good choice

17. Max Plank - Quantum Theory Black Body Radiation This is Plank’s Law - it relates an objects temperature to its spectrum 8/23/2015Website - dmradas.co.uk17 1mm wavelength Microwaves This LAW applies to THERMAL RADIATION Intensity

18. Approximation for Thermal Black Bodies At long wavelengths the Plank Law is approximated to by the simpler Rayleigh -Jeans Law 8/23/2015Website - dmradas.co.uk18 VHF Microwave 10GHz20GHz1GHz100MHz Spectral Intensity By measuring here we can determine the temperature of a body – The Sun / the ground Measure this Know this Calculate this

19. 8/23/2015Website - dmradas.co.uk19 Radio signals from the Sun There are two types of radio emission from the Sun Quiet sun - no sunspots Storms on the Sun producing bursts of radio signals Thermal ‘Black Body’ body Non Thermal ‘Synchrotron Radiation’

20. 8/23/2015Website - dmradas.co.uk20 What we will be measuring We will point the dish near the Sun and let the rotation of the Earth transit the Sun across the receiver beam We will get a trace of signal strength like that shown below We cam measure the temperature of the Sun

21. Dish Pointing South Beam direction 2012 Radio Astronomy Group

22. Beam direction South East West Dish Orientation 2012 Radio Astronomy Group

23. Power Supply Post Detector Electronics Digitiser Detector Post Detector Electronics 11GHz Telescope Receiver Configuration Microwave receiver 2012 Radio Astronomy Group

24. ~ 3 degrees Raster Scan Components across Sun at various elevations 13/6/07 2013 Making Radio Maps of objects

26. 6.6 Degs Solar Imaging @ 11GHz using Automatic Scanning of Antenna Optical Diameter of Sun= 0.53 0 The size of the image is dominated by Amstrad Dish Beamwidth of 3.17 0 Dish Beamwidth of 3.17 0 2013 Making Radio Maps of objects

27. 140150160170180190200210220 15 20 25 30 35 40 45 Azimuth Angle (degrees) Elevation Angle (degrees) Survey of Broadcast Satellites from 140 0 –220 0 Azimuth & 15 0 – 43 0 Elevation Auto Scan equipment with Amstrad 60cm Dish @ 11042MHz (-3dB BW= 3.17 0 ) Icom-R7000FM, 1292MHz IF, TC=3, 4 min/ Scan sweeprate, ~12:00BST 16/6/07 (Satellite Sources deliberately overexposed to reveal background levels) S1 S2 S3 S4 S5? Wooden Pole 2013 Making Radio Maps of objects

28. 8/23/2015Website - dmradas.co.uk28 Radio Astronomy The Large Radio Telescope at Jodrell Bank in Cheshire

29. Last Years Build Activity The 2012 group built two small dish type radio telescopes from Satellite TV components The built the post detector electronics Constructed a simple dish elevation mechanism Did not have time to make useful measurements This years task is to obtain and publish plots of the SUN, the general microwave sky, and if possible the Moon The next few slides show what the 2012 group did 8/23/2015Website - dmradas.co.uk29

30. 8/23/2015Website - dmradas.co.uk30 Find out what comes out of the detector Lets connect up the receiver and detector and examine the output voltage with an oscilloscope +13.8V power Output signal oscilloscope receiverdetector Sensitivity control

31. 8/23/2015Website - dmradas.co.uk31 Components needed for the electronic circuit Components include: Resistors Capacitors Electrolytic capacitors Operational Amplifier chips Voltage regulation chips Variable resistors Switch Connectors + - + - out 7805 com ip op

32. 8/23/2015Website - dmradas.co.uk32 Basic definitions DC current is ‘Direct Current’ it has a fixed value with time AC current is ‘Alternating Current’ it varies with time Current I Amps Time secs Current I Amps Time secs Period = x milliseconds Frequency = 1/x

33. 8/23/2015Website - dmradas.co.uk33 What do these components do ? A resistor reduces current in a circuit - is not affected by frequency +V V=10 V R =10  I=1 amp OHMS LAW I = V / R A capacitor conducts more current at high frequencies Current varies with frequency (higher current at higher frequency) Impedance (  ) = 1/ 2  f C +V V=10 Vpk-pk AC signal source C= 1  F I Impedance (  ) Frequency Hz

34. 8/23/2015Website - dmradas.co.uk34 Variable resistor - Voltage divider Variable resistor – simply what its name suggests +V V=10 V R =10k  V=10 V V=5 V Half way along resistor (5k  ) 10k R1= 8k R2= 2k Voltage V Voltage v = V x 2/8 = 1/4V Generally v = V x R2 / R1

35. 8/23/2015Website - dmradas.co.uk35 Integrated circuits - ‘chips’ The type we use is called an Operational Amplifier It is a general purpose amplifier where the ‘gain’ can be varied It has two inputs (one =+ve, one -ve) and an output Increase voltage on + ve input – output increases Increase voltage on - ve input – output decreases

36. 8/23/2015Website - dmradas.co.uk36 CA3140 Operational Amplifier This is what is inside the chip

37. 8/23/2015Website - dmradas.co.uk37 ‘Op Amp’ theory The amount of amplification is fixed by the ratio of two resistors input output R1 R2 Operational Amplifier Gain = 1 +R1/R2 Basic Operational Amplifier Circuit +V -V 0V Gain = output V / input V Gain = 100x say Gain = 20log 100 = 40dB An Operational Amplifier is a basic high gain device (x 1000) with feedback terminals - feedback +feedback Connecting a fraction of the output to the – feedback input reduces the gain R1 / R2 is a potential divider

38. 8/23/2015Website - dmradas.co.uk38 What does the electronics have to do? Filter out noise from the detector - leave a ‘clean’ DC voltage Remove any ‘base voltage’ level from the detector – set zero volts Apply more variable filtering to suit observation conditions Amplify the voltage from 0.3 V up to 9V at the output FILTER Set offset voltage Amplify difference x 2 Vary amplify by up to10x or up to 20x Variable filter time constant Output 0 to 9V Input up to 0.3V but with an offset

39. 8/23/2015Website - dmradas.co.uk39 Circuit Blocks FILTER Voltage regulator Second Voltage regulator Set offset voltage Amplify Difference x 2 Switch various Time constants Vary amplify by up to10x or up to 20x Signal input Signal output

40. 8/23/2015Website - dmradas.co.uk40 The circuit 7805 100k 10k 1k 10k.22uF com ip op 330k 1uF 330k 2 2 3 3 4 4 7 7 1 6 6 output input 0 to +0.3V 0 to 9V Gain Gain switch Time constant 7810 com ip op 10V 13.5V To LNB 1000uF 16V 0V Post Detector Signal Conditioning Amplifier For use with Ku Band Satellite Finder CA3140EZ * * * 10 turn potentiometer Voltmeter

41. 8/23/2015Website - dmradas.co.uk41 How to plan a circuit board Use circuit board like grid map Generally components placed vertically Power ‘rails’ horizontal - green & red) Connections between circuit sections - horizontal (yellow) Notch is at the top +ve power ‘rail’ 0V power ‘rail’ Wire link

42. 8/23/2015Website - dmradas.co.uk42 Cutting copper tracks Sometimes need to cut copper ‘tracks’ to isolate parts of circuit Part of circuit 1 Part of circuit 2 Cut track with drill bit in hole

43. 8/23/2015Website - dmradas.co.uk43 Design an elevation drive system Elevation arm - mechanical design This is one way to do the job - there are others This pivot is free to rotate This nut is welded to the bracket These lock nuts push against the bracket This bracket is free to rotate Screw thread feeds through fixed nut and pushes the locknuts Screw thread feeds through fixed nut and pushes the locknuts

44. 8/23/2015Website - dmradas.co.uk44