8/23/2015website - dmradas.co.uk1 radio astronomy david morgan
TRANSCRIPT
04/19/23 Website - dmradas.co.uk 1
Radio Astronomy
Radio AstronomyRadio Astronomy
David Morgan
04/19/23 Website - dmradas.co.uk 2
Radio Astronomy - part 1Radio 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
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Radio AstronomyRadio 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 – 30K Microwave Background
Cosmic Microwave Background
Combined optical & Radio
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Radio Astronomy - Radio Astronomy - BeginningsBeginnings
Karl Jansky 1931 20MHz
Bell Labs accidental discovery of cosmic radio signals
Grote Reber 1937 160 & 480MHz
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Radio AstronomyRadio Astronomy
My early attempts at Radio Astronomy at school
15 foot dia. Antenna skeletonMe Mr WilkinsReceiver – made from bits of TV sets
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Large TelescopesLarge Telescopes
Jodrell Bank Radio telescopesCentral Mast
Mk 1
The Feed
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Radio AstronomyRadio Astronomy
My 3m dia dish with 1.4GHz Feed
f/D=0.28 beamwidth = 50 Gain = 30dB or 1000 times
Frequency in MHz = 300 / Wavelength in metres
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Radio AstronomyRadio Astronomy
Natural Ambient Radio Noise - Low Noise region
An
ten
na
Te
mp
era
ture
0 K (
no
ise
le
ve
l)
Wavelength
Radio noise powercan be expressed as anequivalent temperature
P = K TB
P = noise power
K= Boltzmans Const.T = Temperature 0KB = bandwidth
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Radio AstronomyRadio Astronomy
GdirGref
SSource SatmosS EMIMan
Ground Temp = TG 0K
Low Noise Amp
Noise AMP
Pout
Pout = Ss +Sa+SEM +IM +(Gd +Gr) + NAMP Depends on TG
Total Power Receiving System - Signal Contributions
All noise sources ‘in grey’must be stable to better than 0.1dB
Feed
Reflector
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Radio AstronomyRadio 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 HeadAmplifier
Cooled HeadAmplifier
Cooled HeadAmplifier
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What are we going to Build ?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
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Receiving SystemReceiving System
The receiver has 6 main components• Dish
• Feed / low noise receiver (LNB)
• Detector
• Post detector amplifier
• Digitiser
• Computer
DetectorPost detector
amplifier Digitiser
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Actual componentsActual components
Examples of system components
Receiver
Detector
Post detection Amplifier
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ChallengesChallenges
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
7805
100k
100k
100k100k10k
1k
10k10k
.22uFcom
ip
op
330k
1uF
1uF
330k
22
33
44
77
16
6
output
input0 to +0.3V
0 to 9V
GainGain switch
Timeconstant
7810com
ip
op10V
13.5V
To LNB
1000uF 16V
0V
CA3140EZCA3140EZ*
*
*10 turn potentiometer
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The amplifierThe amplifier
7805
100k
100k
100k
100k10k
1k
10k10k
.22uF
com
ip
op
330k
1uF
1uF
330k
2
2
3
3
44
7
7
1
66
output
input
0 to +0.3V
0 to 9V
Gain
Gain switch
Timeconstant
7810
com
ip
op10V
13.5V
To LNB
1000uF 16V
0V
Post Detector Signal Conditioning Amplifier
For use with Ku Band Satellite Finder
CA3140EZCA3140EZ
*
*
*10 turn potentiometer
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Observing the SUNObserving 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
Max Plank - Quantum Theory Black Body RadiationMax Plank - Quantum Theory Black Body Radiation
This is Plank’s Law - it relates an objects temperature to its spectrum
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1mmwavelength Microwaves
This LAW applies to THERMAL RADIATION
Inte
nsity
Approximation for Thermal Black BodiesApproximation for Thermal Black Bodies
At long wavelengths the Plank Law is approximated to by the simpler Rayleigh -Jeans Law
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VHFMicrowave
10GHz20GHz 1GHz 100MHz
Spe
ctra
l Int
ensi
ty
By measuring here we can determine the temperature ofa body – The Sun / the ground
Measure this
Know this
Calculate this
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Radio signals from the SunRadio 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’
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What we will be measuringWhat we will be measuring
Meas urement of the S UN pas s ing throug h 1m dis h B eam11G Hz meas urement on 3/5/2012 (Monmouth S c hool)
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
1 601 1201 1801 2401 3001 3601 4201 4801 5401 6001 6601 7201 7801 8401
Sig
nal
Str
eng
th (l
inea
r)
T ime s econds x 10 (s ample rate is 10/s econd)
-3dB (x.7071)
0.75 degrees-3dB B eamwidth = 1.5 deg s
Half full beam width= 3.6 degs
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
Dish Pointing South
Beam direction
2012 Radio Astronomy Group2012 Radio Astronomy Group
Beam direction
South
East
West
Dish Orientation
2012 Radio Astronomy Group2012 Radio Astronomy Group
Power Supply
Post DetectorElectronics
DigitiserDetector
Detector
Post DetectorElectronics
11GHz Telescope Receiver Configuration
Microwave receiver
2012 Radio Astronomy Group2012 Radio Astronomy Group
~ 3 degrees
Raster Scan Components across Sun at various elevations 13/6/07
2013 Making Radio Maps of objects2013 Making Radio Maps of objects
2013 Making Radio Maps of objects2013 Making Radio Maps of objects
6.6 Degs
Solar Imaging @ 11GHz using Automatic Scanning of Antenna
Optical Diameter of Sun= 0.530
The size of the image is dominated by Amstrad Dish Beamwidth of 3.170Dish Beamwidth of 3.170
2013 Making Radio Maps of objects2013 Making Radio Maps of objects
140 150 160 170 180 190 200 210 220
15
20
25
30
35
40
45
Azimuth Angle (degrees)
Ele
vati
on
An
gle
(d
egre
es)
Survey of Broadcast Satellites from 1400 –2200Azimuth & 150 – 430 Elevation
Auto Scan equipment with Amstrad 60cm Dish @ 11042MHz (-3dB BW= 3.170)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
S3S4
S5?
Wo
od
en P
ole
2013 Making Radio Maps of objects2013 Making Radio Maps of objects
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Radio AstronomyRadio Astronomy
The Large Radio Telescope at Jodrell Bank in Cheshire
Last Years Build ActivityLast 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
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Find out what comes out of the detectorFind 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
receiver detectorSensitivity control
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Components needed for the electronic circuitComponents 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
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Basic definitionsBasic definitions
DC current is ‘Direct Current’ it has a fixed value with time
AC current is ‘Alternating Current’ it varies with time
Cur
rent
I
Am
ps
Time secs
Cur
rent
I
Am
ps
Time secs
Period = x millisecondsFrequency = 1/x
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What do these components do ?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 LAWI = V / R
A capacitor conducts more current at high frequencies
Current varies with frequency(higher current at higher frequency)
Impedance () = 1/ 2f C
+V
V=
10 V
pk-p
k
AC signalsource
C= 1F
I
Imp
edan
ce (
)
Frequency Hz
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Variable resistor - Voltage dividerVariable 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)
10kR1= 8k
R2= 2kVol
tage
V
Voltage v = V x 2/8 = 1/4V
Generally v = V x R2 / R1
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Integrated circuits - ‘chips’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
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CA3140 Operational AmplifierCA3140 Operational Amplifier
This is what is inside the chip
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‘‘Op Amp’ theoryOp Amp’ theory
The amount of amplification is fixed by the ratio of two resistors
inp
ut
ou
tpu
t
R1
R2
OperationalAmplifier
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 Amplifieris a basic high gain device
(x 1000) with feedback terminals
- feedback
+feedback
Connecting a fraction of the outputto the – feedback input reduces the gain
R1 / R2 is a potential divider
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What does the electronics have to do?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
FIL
TE
R
Set offsetvoltage
Amplifydifference
x 2
Vary amplify by up to10xor up to 20x
Variablefiltertime
constant
Output0 to 9V
Inputup to 0.3Vbut with an offset
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Circuit BlocksCircuit Blocks
7805
100k
100k
100k
100k10k
1k
10k10k
.22uF
com
ip
op
330k
1uF
1uF
330k
2
2
3
3
44
7
7
1
66
output
input
0 to +0.3V
0 to 9V
Gain
Gain switch
Timeconstant
7810
com
ip
op10V
13.5V
To LNB
1000uF 16V
0V
Post Detector Signal Conditioning Amplifier
For use with Ku Band Satellite Finder
CA3140EZCA3140EZ
*
*
*10 turn potentiometer
FILTER
Voltageregulator
SecondVoltageregulator
Set offsetvoltage
AmplifyDifference x 2
Switch variousTime constants
Vary amplify by up to10xor up to 20x
Signalinput
Signaloutput
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The circuitThe circuit
7805
100k
100k
100k
100k10k
1k
10k10k
.22uF
com
ip
op
330k
1uF
1uF
330k
2
2
3
3
44
7
7
1
66
output
input
0 to +0.3V
0 to 9V
Gain
Gain switch
Timeconstant
7810
com
ip
op10V
13.5V
To LNB
1000uF 16V
0V
Post Detector Signal Conditioning Amplifier
For use with Ku Band Satellite Finder
CA3140EZCA3140EZ
*
*
* 10 turn potentiometer
Voltmeter
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How to plan a circuit boardHow 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
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Cutting copper tracksCutting 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
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Design an elevation drive systemDesign 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 bracketis free
to rotate
Screw thread feeds throughfixed nut and pushes thelocknuts
Screw thread feeds throughfixed nut and pushes thelocknuts
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