Amateur Radio Astronomy

319 Pages·2016·14.97 MB·English

AMATEUR
RADIO
ASTRONOMY
BY JOHN FIELDING, ZS5JF
^
-i fV'\V
Published bythe Radio Society ofGreat Britain, 3 Abbey Court, Priory Business
Park, Bedford MK44 3WH
First published 2006
Reprinted 2006, 2007 & 2008
© Radio SocietyofGreat Britain 2006.All rights reserved. No partofthis publication
may be reproduced, stored in a retrieval system, ortransmitted in anyform, orby
anymeans, electronic, mechanical, photocopying, recording orotherwise, without
the priorwritten agreementofthe Radio SocietyofGreat Britain.
ISBN 9781-905086-16-0
Publisher’snote
The opinions expressed in this book are those ofthe authorand not necessarily
those ofthe RSGB. While the information presented is believed to be correct, the
author, publisherand their agents cannot accept responsibilityfor consequences
arising from any inaccuracies oromissions.
Production: MarkAllgar MlMPA
Sub-editing: George Brown, M5ACN / G1VCY
Coverdesign: Dorotea Vizer, M3VZR
Typography and design: Mike Dennison, G3XDV, Emdee Publishing
Printed in Great Britain by LatimerTrend & Company Ltd of Plymouth
This book has a supporting website:
http://www.rsgb.org/books/extra/arastronomy.htm
Any corrections and points ofclarification that have not been incorporated in this
printing ofthe book can be found here along with any supporting material that
may have become available
Contents
• Foreword 1
1 A Brief History of Radio Astronomy 5
2 Radar Astronomy 35
3 Receiver Parameters 73
4 Antenna Parameters Ill
5 Early Low Noise Amplifiers 165
6 Assembling a Station 173
7 50MHz Meteor Radar System 185
8 Practical Low Noise Amplifiers 213
9 Assessing Receiver Noise Performance 235
10 Station Accessories 247
11 Low Frequency Radio Astronomy 253
12 The Science of Meteor Scatter 259
13 A Hydrogen Line Receiving System 283
• Appendix: Further Information 309
Index

hewritingofthis booktookapproximately threeyears ofmy sparetime.
Theresearchperiodstretchesback 10yearsormoreandisstillongoing.
I waspersuaded towritesuch abookbecausethere is notan equivalent
one, dealing with radio astronomy from the radio amateur's perspective. There
areothers,butthesefocusontheamateurastronomer,thosepeoplewhoalready
have an interest in the observation ofthe galaxies via optical means.
Let me first ofall dispel any idea thatI am an astronomer. Nothing could be
furtherfromthetruth, Thaveneverclaimedto be. I simplyhave a strong desire
tounderstand theradiofrequency engineeringaspects ofwhatmake radiotele-
scopes work and how to improve the engineering side. My professional career
stretches back over 30 years in the radio frequency engineering design and
developmentfield. During that time 1 have been aradio amateur, first licensed
in 1972, although1 passedthe RadioAmateurs Examination in 1969.
During myperiodofworkingforvarious companies, 1have foundthatbeing
a 'ham' has given me a better insightinto some ofthe engineeringtasks 1 have
had to face. My approach has always been based on the KISS principle (Keep
It Simple- Stupid), andthatover-engineeringdoesnotmake apoordesign into
agoodone.Manyofmyformercolleaguesfailedtograspthenecessityofmak-
ingthe fewestcomponents do themaximumamountofwork. Ihaveworkedon
some very complex design and development problems, often with a limited
timescale and budget, andhave always managed to get through it to the satis-
faction ofmy employers and customers.
Theotherpitfallintowhichsomedesignengineersfallisusingcomponentsthat
costmorethanisnecessary. Inthe defenceindustry,whereTspentmostofthe30
years,thisis oftenunavoidablebecause ofthe specifications thathaveto be met,
both electrically and environmentally. However, ifyou can substitute lower-cost
components, with an equivalent specification, you can save a huge amount of
money on high-volume production runs. Some ofmy former colleagues didn't
have any idea ofthe cost ofcertain components; they simply drew components
from the stores because they were there. 1 proved on several occasions that, by
changingsome componentsto industrial orautomotive grade, a significant cost-
savingcould be achieved. T supposepart ofthis is duetomy Scottishancestry!
Being a radio amateur in this type ofenvironment is a sort ofbusman's holi-
day, but I have achieved deep satisfaction from my constructional work and
experimenting in my shack. Being not only electronically-minded but also
somewhat skilled in the mechanical field is a double blessing. I can usually
visualise inmy headwhat the finished productwill look like and how itwill all
fit together, even before 1 have started designing. I also have a fairly well-
equipped workshop w'here 1 can make most of the mechanical components
needed for my constructional projects.
AMATEUR RADIOASTRONOMY
Inevitably, as a book ofthis sort evolves, certain changes will occur in the
structure or presentation as new developments occur or other facts come to
light. Oneofthemanyproblems isbeing able to quotethenames ofcomponent
manufacturers andpart numbers. The lastfiveto 10yearshave seen a complete
upheaval inthetraditional electronics field. Manyofthehousehold nameshave
gone,often swallowedup in atake-overbyanotherconglomerate. Forexample,
RCA, who made RF transistors and other semiconductors were bought out and
the name changed to Harris. No sooner had this happened than another name
changeoccurredtoIntersil.Thisseemstobeacommonfeaturetoday,thenames
yourelied ontosupplydataandsamplesfordevelopmentare suddenlymissing.
Another curse ofthe industry is the sudden discontinuation ofa device. The
microprocessormanufacturers seemtodo thisquiteregularly, butitalsoapplies
totheRFsemiconductorindustry. Onanumberofoccasions,Ihavehadaprod-
uctjustaboutreadyto startproductionwhen itis foundthatsome key device is
on a 'last-buy' schedule. Myreasonformentioning this unhappy state ofaffairs
isthat,throughoutthebook,Ihavegivenexamplesofsuitablepartnumbersand
manufacturers names. If, after the book is published, some of these parts
become obsolete, 1have no control overthat fact. I have endeavouredto quote,
to the best ofmy knowledge, correct part numbers and current manufacturers'
names as at the time ofwriting.
Usually, when a part goes out ofproduction, the manufacturer will recom-
mend a direct- ornear-replacement. Unfortunately, the sort ofcomponents that
amateurconstructorsuse (deviceswithleads) are gettingscarcer, asthe general
trend is towards surface-mount technology and many ofthe older devices are
now only available as SMD types. Electrically they are the same, but much
smaller and more difficult to use breadboard-style. For a one-offitem for the
shack,abreadboardtypeofconstructionisusuallyquiteadequate;aslongasthe
circuit performs the way it should, there is no needto spend money on printed
circuitboards unlessyouintendtomass-producethe item. Ifyouare likeme,of
'mature years', you will sympathise with the constructor with poor eyesight,
handlingminute components underamagnifying glass!
Anotherfactordrivingthesemiconductorindustryisthemass-market. Indays
gone by, this was nearly always the defence industry. With the gradual down-
turnofthisfield,thesemiconductormanufacturershavemademanyoftheolder
devicesobsoletebecauseofeconomicfactors.Today,themassmarketisthecel-
lulartelephone industry. Hence,youwillfindadearthofRF devices forthetra-
ditional 450MFIz equipment, but a vast variety of900MHz devices for GSM
handsets. This is good and bad for the amateur constructor. Many of the
900MHz parts will work quite well at 432MFIz and 1296MHz. With the GSM
handsetmarketexpanding into the 1.8GHz and 2.4GHzregions, this is a bless-
ing for amateurs active at these frequencies.
Thepresentation ofinformation is not easyforthetarget market. Some ama-
teurs might be practising engineers in a specialised field, others might be what
most ofthe general public regard as 'hams' and work in ajob with no contact
with technology, but use amateur radio as a way to unwind from the day's
stresses. Becauseofthis,thedangeristogiveeithertoolittleortoomuchdetail.
Givingtoo littledetailisworsethantoomuch; thereaderisleftwithmoreques-
tions. I have tried to avoidthis bythe use ofshaded panels. Often1 canrecount
2
FOREWORD
an amusing incident connected with the topic, or give some historical back-
groundto thewaythetechnologyevolved. Abookdoesnotneed to bedull and
heavygoing; some humourlifts the reader aftera deeply technical portion.
History is a powerful tool for the design engineer. Many times 1 have met
newly-graduatedjunior engineers, excited about a new idea they have come up
with. Upon listeningtotheirideayourealiseitisn'tnewatall-wediditthatway
20 years ago! Without some historical background in a topic you can follow a
dead-end pathuntilyourealisetheideawill neverwork. Ihavebeenfortunateto
have shared my working time with many older engineers, who not only taught
me things I didn'tknow, but gave me some valuable insight into the pasthisto-
ry ofatopic. Consequently,the first few chapters coverthe historical course of
radio astronomy from its beginning, and I add extra historical details when I
believe itwill aid the readerto understandthe subjectbetter.
There is an old saying'there isnothingnewunderthe sun'. This factcrops up
time and again. In 1903, a German engineer by the name of Christian
Hulsmeyerproposedtheuseofradiowavesto detectthemovementofships;he
builta crude version, tookouta British patentand demonstrated it, no onewas
interested. In 1922 Marconi proposed the same idea again - no one listened.
Only after the ionospheric sounders (built to try to understand how the ionos-
pheric layers affect radio waves in 1925) showed a return echo, was the first
radar'invented'. Laterin 1937,withtheobviousthreatofWorldWarII looming,
the British defence industry rushed to develop radar for military purposes. It
was all available in 1903 but no one took any notice. There are many people
who believe that SirRobert Watson-Wattwas the fatherofradar, this is simply
untrue. Watson-Watt simply used known technology to design the early British
'Chain Home' system during the run up to World War II. He had been asked by
the Tizard Committee to develop a 'death-ray' transmitter to bum up German
aircraft. When he explained this was impossible with the available technology
he countered the request by pointing out that with the available technology it
would be betterto use this formore elaborate direction-finding equipment. He
had spent many years developing equipment to track thunder storms. So the
birth ofradar began quite late in the British scientific circles.
I cannot finish this foreword without giving acknowledgement to some peo-
ple ororganisations thathave given me invaluable assistance in compiling this
work. Ihavereliedon data fromagreatnumberoftextbooks, magazinearticles
and other amateurpublications to collect the necessary information. Wherever
possible, I have tried to acknowledge the source. I should like to personally
thankthe following:
Chris Leah - for his assistance with the chapter on radar and the loan ofsev-
eral text books; Stuart MacPherson, ZR5SD, Director ofElectronics, Durban
Institute ofTechnology - forreviewingthe technical portions; Dr Gary Hoile -
for his suggestions on the sections covering power amplifiers; David Joubert -
forsuggestions coveringthe signal processing aspects; SirBernard Lovell - lor
inspiring me to become interested in radio astronomy and for providing some
historical data on the early Jodrell Bank equipment; the University of
Manchester, Jodrell Bank and the Lovell Radio Telescope - forassistance with
historical pictures. Derek Barton - for identifying the radar system used by
Lovell; the UK Ministry ofDefence for supplying technical details ofthe GL2
3
AMATEUR RADIO ASTRONOMY
radar system from its archives; LewPaterson ofRAF Cranwell forfurther his-
torical information on the early radardevelopmentand forcorrecting some fac-
tual items on the GL2 radar system; DrGraham Elford ofAdelaide University,
Australia, forsupplying details ofmodem meteor-detection radarand themete-
ortrail topic.
I would also like to express my sincere gratitude to the specialists at the
UniversityofManchester,Jodrell BankRadio Observatory, especially Tim Ikin
and his team who afforded me numerous hours oftheir limited time to explain
difficultdetails in layman'sterms, andtoJanetEaton - Sir BernardLovell's sec-
retary-who assistedwithmysearchthroughthearchived artefacts. Duringthis
search, some veryrarephotographswere uncovered thathavenot seenthe light
ofdayforover50years. Someofthesearereproduced inChapter 1. Duringmy
visits, Iwas also privilegedto be shown the new development workbeingdone
ontheverylow-noisefront-endunitsthatuseliquidhelium coolingandoperate
on frequencies up to 44GHz. These will soon fly on a new satellite to explore
theL2region in deep space, aprojectsponsored bythe Max Planck Institute in
Bonn, Germany.
Finally,butbynomeansleast,mydearwifePenny, forencouragingme inthe
long period Itookto write itall down.
I dedicatethisbook in memory ofall those'amateurs' whoplayed a small but
vital part in the science ofRadioAstronomy.
John Fielding, ZS5JF
Monteseel
SouthAfrica
2005
4
A Brief History of Radio Astronomy
In this chapter:
Pioneers Thebirth ofthe big telescope
Thewaryears Lunarradar-moonbounceorEME
Germanwartimeradar
his is a fascinatingperiod inthe developmentofthe scienceand, aswill
be seen, although some ofthe results confirmed earlieroptical observa-
tions, many experiments gave conflicting answers and, in many cases,
opened up further areas of investigation, some of which are still on-going.
Manyamateurradiooperatorsfiguredintheearlyperiod andwith theiraptitude
for problem-solving and constructing complex equipment, the science
advancedrapidly.
PIONEERS
Guglielmo Marconi
AlthoughMarconi isnot consideredbymany people to havemade any signifi-
cant input to astronomical science,this is not so. Due to hispioneeringwork in
demonstrating that trans-Atlantic radio communications was possible, the sci-
entific world atthe time then hadto explain how itwas possible.
Up until 1901, when Marconi and his colleagues succeeded in sending radio
signals across the Atlantic from Poldhu in Cornwall to Newfoundland, the
belief was that radio waves, like light waves, only travelled in straight lines.
Alterhis success, the scientificworld was leftwith theproblemofhowthishad
occurred, and fairly soon it became apparent that the radio waves were being
bent or refracted by the upper atmosphere. This refraction was deduced to be
duetotheeffectofthe Sun'sultra-violetradiationreleasingfreeelectrons in the
rarefied upper atmosphere, the ionosphere, to behave like a radio 'mirror1,
allowing radio waves to be returned to earth at great distances from the source.
From the 1920sto thepresentday, thescience oftherefractingmechanism in
the ionosphere has been studied using ionospheric sounding apparatus, both
AMATEUR RADIO ASTRONOMY
fromthesurface oftheearth and from soundingballoonsandrockets. The early
resultfrom these studies wasthatradiowaveswere unable to penetratethe ion-
osphere and hence were prevented from passing into space. This theory was
turned on its head a few years later!
Marconi developed a practical microwave link tojoin the Italian telephone
network tothe summerresidence ofthePope and, in 1922, proposed theuse of
radio waves to detect objects, manybelieve this to be the first attemptat radar.
Although Marconi did not find much favour for his idea, this was taken up by
others and pursuedto its conclusion.
In an address to the American Institute of Radio Engineers (IRE) in 1922
Marconi stated:
"As was first shown by Hertz, electric waves can be completely reflected by
conducting bodies. In some ofmytests, I have noticed the effects ofreflection
and detection ofthesewaves bymetallic objects miles away.
"It seems to me that it should be possible to design apparatus by means of
which a ship could radiate or project a divergent beam ofthese rays in any
desireddirection; whichrays, ifcomingacross ametallicobject, such as anoth-
ersteamerorship, wouldbereflectedbacktoareceiverscreenedfromthe local
transmitter on the sending ship, and thereby, immediately reveal the presence
and bearingofthe othership in fog orthickweather."
Marconi had obviously not heard of Christian Hulsmeyer or his patent of
1903 where he not only proposed the idea but also built a working system and
demonstrated it.
In the light of Marconi's address, two scientists at the American Naval
Research Laboratory (NRL) determined that Marconi's concept was possible
and, laterthatsameyear(1922), detectedawoodenship atarangeoffive miles
using awavelength of5m using a separate transmitter and receiver with a CW
wave. In 1925, the first use ofpulsed radio waves was used to measure the
heightofthe ionospheric layers, radarhadbeen bom. (RADAR isthe acronym
forRadioDetection and Ranging.)
Karl G Jansky - USA
Between 1930 and 1932, Karl Jansky, an engineer working for the Bell
Telephone Corporation Laboratory, (BTL) in Belmar, New Jersey was investi-
gatingtheproblemofinterferenceto long-distanceHF ship-to-shoreradio links.
This took theform ofbursts ofnoise orahissingsound andwas seeminglyofa
randomnature.
In orderto study this interference, Jansky constructeda large multi-loop Bruce
antenna array supported on a frameworkofwood and mounted this on old Ford
Model T wheels to allow it to be rotated and pointed in various directions, this
becameknownasJansky's'merry-go-round'. ItwassetupinapotatofieldinNew
Jersey. The antenna andreceiverworkedon afrequencyof20.5MHz(14.6m).
Jansky discovered that the noise emanated from two different sources, light-
ning-induced noise(atany onetimethereareanestimated 1,800differentlight-
ning storms in existence), and also anoise that appeared when the antennawas
pointed inaparticulardirectionatthesametimeevery day,butJanskycouldnot
immediately correlate this to any known source. Further careful observations
showedtheratherstartling fact that the time between successivepeaks was not
24hoursbutwas 23 hours and57 minutes, which isthetimetakenforthe earth
6