how to build your own radio telescope sample

7/27/2019 How to Build Your Own Radio Telescope Sample

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HOW TO BUILD YOUR OWN

RADIO TELESCOPE

Percival Andrews


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First edition 2007

Revised 2007

Copyright text

Percival Andrews, 2007

Copyright photographs, diagrams, and illustrationsPercival Andrew, 2007, except where otherwise credited

All rights reserved. Without limiting the rights under copyrightreserved above, no part of this publication may be transmitted inany form without the prior written permission of PercivalAndrews

The radio telescope described in the book is very low power andtherefore quite safe. The following precautions will ensuretrouble-free operation:

1. Be aware that the antenna could be a hazard during athunderstorm. You should disconnect the antenna during athunderstorm, especially if it is outdoors

2. The solar storm radio telescope connects to a PC via a soundcard. You can make use of an inexpensive external USB sound

card if you don't want to connect anything directly to your PC

This book contains instructions, schematics, and computerprograms for use in amateur radio telescope and computerinterface projects. The content of the book is to be consideredexperimental only, and the authors make no claims as to thefunctionality of actual working models made from theinstructions in this book. The reader is expressly warned toconsider and adopt all safety precautions that might be indicated

by the activities herein and to avoid all potential hazards. Byfollowing the instructions contained herein, the reader willinglyassumes all risks in connection with such instructions.

Information contained in this book has been obtained fromsources believed to be reliable. However the author does notguarantee the accuracy or completeness of the informationcontained herein, and the author shall not be responsible for anyerrors, omissions, or damages arising out of the use of thisinformation.


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THIS IS A SAMPLE, PLEASE VISIT

http://www.radiotelescopebuilder.com

FOR THE FULL VERSION
http://www.radiotelescopebuilder.com/http://www.radiotelescopebuilder.com/


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Contents

1 Why build a radio telescope?

2 Introducing the Solar Storm Radio Telescope (SSRT)

3 What youll need to build the SSRT

4 Finding a suitable radio transmitter

5 Building the on-board electronics

6 Building the antenna

7 Installing the radio telescope

8 Installing the PC software and finding the signal

9 Optimizing the performance of the radio telescope

10 Interpreting the radio telescope signal

11 What next?

A1 System diagram

A2 Electronic schematic diagram

A3 Electronics parts list

A4 Signal generator

A5 Data collection for the AAVSO


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1. Why build a radio telescope?

Radio telescopes are critical forscience and astronomy

It was an experimental radio antennaoperating in New Jersey in 1964 that firstdetected the Cosmic MicrowaveBackground Radiation. These microwaves,permeating through space in all directions,provided the original piece of experimentalevidence for the theory of the Big Bang.The discoverers, Arno Penzias and Robert

Wilson, received the Nobel Prize forPhysics in 1978 for their finding.

This is just an example, of course, and whilst Im not suggestingthat your radio telescope project is going to lead to anotherNobel Prize, I can guarantee that you are about to embark on anexciting journey of learning and discovery.

The sun is one of the most interesting subjects in radioastronomy

Sunspots and solar storms have some surprising effects here onearth. A study of agricultural markets in the 17th centuryshowed that crop yields were higher and grain prices lowerduring years with high sunspot activity. Its still a mystery how

this can happen, but sunspots must clearlyinfluence the weather. A study of theTexas electricity market in recent yearsshowed that solar storms reduced theefficiency of transformers in the electricitydistribution grid and increased the price of

electricity. Events can be more dramatic.On October 29th, 2003 the $450 millionJapanese weather satellite Midori 2 wasknocked permanently out of action by asolar storm, and on December 6th, 2006the Global Positioning Satellite (GPS)system was disrupted by a solar storm.

In the next chapter Ill explain how the easy-to-build Solar StormRadio Telescope that I describe in this book will let you monitor

these events as they happen. Youll build up your own records ofthe solar storms that rage in the atmosphere above your home,

Fig 1.1. Theexperimental radioantenna that firstdetected theCosmic MicrowaveBackgroundRadiation in 1964and won ArnoPenzias andRobert Wilson theNobel Prize.

Fig 1.2. The Midori2 satellite beforebeing disabled by asolar storm. Credit

JAXA


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and be able to share that information with others automaticallyover the internet. First lets look at some of the phenomena thatare associated with solar storms.

Sunspots

These are dark blotches on the surface ofthe sun that are cooler than theirsurroundings. They are caused bychanges in the convection currents thatbring the suns heat from the interior tothe surface.

Solar flaresSolar flares occur when magnetic fieldlines on the surface of the sun that have

become compressed and distorted in theregion of a sunspot suddenly reconnectwith an explosive release of energy.Temperatures in the region reach morethan 10 million Kelvin, and a burst of X-

rays is shot out into space over a period of several minutes.

Usually solar flares pass away harmlessly into space, butoccasionally the Earth will lie in the line of fire. It takes about 8minutes for the X-rays to travel across the 150 million km

between the Sun and the Earth. When the X-rays hit the ionizedtop layer of the Earths atmosphere, the ionosphere, they createan electrical disturbance. The arrival of these powerful X-raysand the dynamism in the atmosphere that they create is knownas a solar storm.

Coronal mass ejectionsTheseare sudden ejections of chargedparticles from the Suns upper atmosphere(the corona). In a typical coronal mass

ejection about 10 billion tons of matter(mainly electrons and protons) are firedaway into space. Like solar flares, coronalmass ejections are likely caused by rapidreconfigurations of the magnetic field lineson the surface of the sun. Coronal massejections create solar storms when theEarth lies in the line of sight of the ejectedparticles.

Solar flares and coronal mass ejections are closely linked to the11 year cycle of sunspot activity. At solar maximum there may

Fig 1.4. A solarflare driven bymagnetic fields

send X-rays intospace. CreditNASA

Fig 1.3. Sunspotare cooler regionsthat appear as darkblotches on thesurface of the sun.Credit: SOHO


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be several solar flares or coronal massejections somewhere on the Sun everyday. At solar minimum there may beweeks between these events. The lastsolar maximum was in 2001. Scientists

have predicted that the next solar cyclewill start its build up in late 2007 or early2008, and may be 30-50% more intensethan the last cycle. So theres never beena better time to build a radio telescope.

Fig 1.5. A coronal mass ejection. The disk of theSun is obscured by the camera. Credit SOHO


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2. Introducing the Solar Storm

Radio Telescope (SSRT)

The SSRT monitors solar storms indirectly by using radiowaves to sense sudden disturbances in ionosphere (SIDs)

The ionosphere is anionized layer in theatmosphere roughly 50-600 km above theEarths surface. Itsionization is caused byincoming UV and X-ray

radiation from the sun.The degree of ionizationincreases with theamount of solarradiation received, andtherefore tends todepend on the latitude,the season, and thetime of day. Ionization

is also dramatically affected by exceptional events such as solar

flares and coronal mass ejections.

The ionosphere is excellent propagator of radio waves. Shortwave communications such the BBC World Service are broadcastacross the globe thanks to the ability of the ionosphere to carryradio waves beyond the transmitters line of sight. The strengthof the propagation by the ionosphere depends on the degree ofionization in quite complex ways that we will examine morecarefully in chapter 10, but the essential point is that short termschanges in the degree of ionization can be detected by

monitoring the changing power of a distant radio signal that isbeing carried through the ionosphere, thus indicating theoccurrence of solar storms.

The kind of radio signal that we would like to monitor is ideallyavailable all over the world, receivable at long range, andtransmitted at constant power. Fortunately such a systemexists. It is the Very Low Frequency (VLF) submarinecommunications network. The VLF band at 3-30 kHz is used forsubmarine communications because only such low frequencies

can penetrate through sea water to be picked up by submergedsubmarines. There are several dozen naval transmitters in use

Fig 2.1. Different

degrees ofionization in theionosphere abovethe Earth showsthe dependence onincoming solarradiation.Credit NASA


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around the world. One of the mostpowerful is the 24 kHz transmitter atCultler, Maine, USA. Another powerfultransmitter is the 22.2 khz transmitter atEbino, Kuyshu, Japan that I monitor.

There are several more in Europe andchapter 4 has an up-to-date list.

Just to reassure you, it is perfectly legal totune into these signals the transmissionsare coded and our simple equipment justmeasures the strength of the signal and

cannot eavesdrop on secret communications. Nobody official orin uniform is going to call on you when you start operating yourradio telescope.

The SSRT produces a diurnal trace that can be interpretedto reveal events such as solar storms

Lets take a quick tour of some typical traces produced by theSSRT and see how they alert us to solar storms. Figure 2.3shows a typical signal received from my SSRT on a quiet day.The local time at the site of the radio telescope in Tokyo, Japanis on the x-axis. The power of the received signal from the VLFtransmitter at Ebino, 900 km away to the south-west is shownon the y-axis. The scale is in decibels, which is simply a

Fig 2.2. VLFtransmissions fromEbino, Kuyshu,Japan propagated

by the ionospherecan be received900 km away inTokyo. Credit:Google Earth

Fig 2.3.Output frommy SSRT ona quiet day.The mainfeature isthe diurnalpatterncaused bythe dailycycle ofsolar UV

irradiationon theionosphere.


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The SSRT can be built simply, using a minimum ofelectronic components, and utilizing your home PC

Now that weve briefly understood what the SSRT is trying to do,lets take a look at what it looks like and how it works. Figure

2.8 is a block diagram that shows the whole system.

The overall scheme starts with an antenna that captures the VLF(Very Low Frequency) signal. The antenna shown in the figure isoutdoors, but an indoor antenna can equally well be used Chapter 6 has details. The received signal at the antenna is veryweak. It is immediately amplified with a simple electronic circuitbased on a common and inexpensive integrated circuit. Theamplifier is powered by a 12V wall-wart transformer or a largebattery. The SSRT is a digital system, and the amplified signal isbrought along a connection cable and digitized by a PCsoundcard. Custom software logs the digitized signal and graphs

it against time to produce charts like the ones shown above.

Antenna Amplifier PC soundcard

Software for

logging and

charting

Captures the VLF

signal by

resonating at the

same frequency

Amplifies the

antenna with a

simple electronic

circuit

Digitizes the

signal using the

line-in or

microphone input

Logs the strength

of the VLF signal

and charts it

against time

Fig 2.8.Blockdiagram ofthe SSRT. Itshows thekeycomponentsof theantenna, theamplifier, the

PCsoundcard,and thesoftware forlogging andcharting

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