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

04/19/23 Website - dmradas.co.uk 1

Radio Astronomy

Radio AstronomyRadio Astronomy

David Morgan


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



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


Radio Astronomy - Radio Astronomy - BeginningsBeginnings

Karl Jansky 1931 20MHz

Bell Labs accidental discovery of cosmic radio signals

Grote Reber 1937 160 & 480MHz



My early attempts at Radio Astronomy at school

15 foot dia. Antenna skeletonMe Mr WilkinsReceiver – made from bits of TV sets


Large TelescopesLarge Telescopes

Jodrell Bank Radio telescopesCentral Mast

Mk 1

The Feed



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



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



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



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




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


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


Actual componentsActual components

Examples of system components

Receiver

Detector

Post detection Amplifier


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


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

*

*



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


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


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


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’


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


Power Supply

Post DetectorElectronics

DigitiserDetector

Detector

Post DetectorElectronics

11GHz Telescope Receiver Configuration

Microwave receiver


~ 3 degrees

Raster Scan Components across Sun at various elevations 13/6/07

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


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




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



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


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


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


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


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


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


CA3140 Operational AmplifierCA3140 Operational Amplifier

This is what is inside the chip


‘‘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


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


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



CA3140EZCA3140EZ

*

*


FILTER

Voltageregulator

SecondVoltageregulator

Set offsetvoltage

AmplifyDifference x 2

Switch variousTime constants

Vary amplify by up to10xor up to 20x

Signalinput

Signaloutput


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



CA3140EZCA3140EZ

*

*

* 10 turn potentiometer

Voltmeter


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


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


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

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

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