Conference PaperPDF Available

An Amateur Instrument for the Detection of the Cosmic Microwave Background

  • July 2017
  • Conference: Society of Amateur Radio Astronomers Annual Conference
  • At: NRAO, West Virginia
Authors:
Jack Gelfand at Central Caribbean Marine Institute, Cayman Islands
Jack Gelfand
  • Central Caribbean Marine Institute, Cayman Islands
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Abstract and Figures

Astronomers detect the Cosmic Microwave Background (CMB) as an extra noise equivalent to a black body radiating at a temperature of 2.73 K. They do this with an instrument called a microwave radiometer. A radiometer is a radio telescope whose response is calibrated with known temperature sources. A professional apparatus utilizes the temperature of liquid helium to calibrate the temperature scale and also to cool the electronics for quiet operation. I have found that one can obtain a reasonable level of performance with inexpensive electronics operating at 10 GHz at ambient temperature and a calibration configuration using liquid nitrogen at 77K.
Cutaway view of the liquid nitrogen cold calibration source
Cutaway view of the liquid nitrogen cold calibration source
… 
A diagram showing the relationship between air mass and observing angle Figure 5 shows the path length in the atmosphere as a function of observation angle. We can see that this path length, called the air mass, is related by the factor Sec θ as shown in Equation 4 below. L(θ) = L(0) Sec θ (4) Where L(0) is the path length through the atmosphere at the zenith and L(θ) is the path length at the observing angle θ. In the Raleigh-­-Jeans approximation the observed temperature grows linearly with airmass as shown in Equation 5. T(Atm, θ) = T(Atm, 0) Sec θ (5) Where T(Atm, 0) is the atmospheric component of the observed temperature measured from the sky at the zenith, and T(Atm, θ) is the atmospheric component of the observed temperature measured from the sky at angle θ. From Eq. 3 and Eq. 5 we can derive a relation expressing the contribution to T(Sky) from T(Atm) shown in Eq. 6 below. Measurements can be made at a number of angles and combined. T(Atm, 0) = [T(Sky, θ) − Τ(Sky, 0)] Cos θ (6)
A diagram showing the relationship between air mass and observing angle Figure 5 shows the path length in the atmosphere as a function of observation angle. We can see that this path length, called the air mass, is related by the factor Sec θ as shown in Equation 4 below. L(θ) = L(0) Sec θ (4) Where L(0) is the path length through the atmosphere at the zenith and L(θ) is the path length at the observing angle θ. In the Raleigh-­-Jeans approximation the observed temperature grows linearly with airmass as shown in Equation 5. T(Atm, θ) = T(Atm, 0) Sec θ (5) Where T(Atm, 0) is the atmospheric component of the observed temperature measured from the sky at the zenith, and T(Atm, θ) is the atmospheric component of the observed temperature measured from the sky at angle θ. From Eq. 3 and Eq. 5 we can derive a relation expressing the contribution to T(Sky) from T(Atm) shown in Eq. 6 below. Measurements can be made at a number of angles and combined. T(Atm, 0) = [T(Sky, θ) − Τ(Sky, 0)] Cos θ (6)
… 
Sequence of antenna positions and sources for calibrating the radiometer A. Ambient temperature absorber mounted at the end of the microwave horn B. Horn antenna aimed into the cold load source at 77K C. Horn antenna aimed at the zenith The electronics in professional equipment are thermostatically controlled. I do not stabilize the temperature of my equipment. I warm up my equipment for at least one hour and try to execute the measurement quickly. I try to avoid times when the ambient temperature is changing rapidly. The input to the Hewlett Packard power meter is reset to zero before each measurement. The stability of the 77 K power reading is a measure of the stability of the entire system as the boiling point of nitrogen is constant. I find that the total power reading is stable to 1% over the course of a one hour data run. IV. Results The analysis of the data and the determination of the measured CMB radiation are best understood graphically. We can construct a graph of microwave noise power versus source temperature as shown in Figure 7 below.
Sequence of antenna positions and sources for calibrating the radiometer A. Ambient temperature absorber mounted at the end of the microwave horn B. Horn antenna aimed into the cold load source at 77K C. Horn antenna aimed at the zenith The electronics in professional equipment are thermostatically controlled. I do not stabilize the temperature of my equipment. I warm up my equipment for at least one hour and try to execute the measurement quickly. I try to avoid times when the ambient temperature is changing rapidly. The input to the Hewlett Packard power meter is reset to zero before each measurement. The stability of the 77 K power reading is a measure of the stability of the entire system as the boiling point of nitrogen is constant. I find that the total power reading is stable to 1% over the course of a one hour data run. IV. Results The analysis of the data and the determination of the measured CMB radiation are best understood graphically. We can construct a graph of microwave noise power versus source temperature as shown in Figure 7 below.
… 
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An#Amateur#Instrument#for#the#Detection#of#the#Cosmic#
Microwave#Background#
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)>#?! GB1(<! 1*<>! 2?#((! IH=#?1+#(! 2-#I'2! >*! <-'! 2B=)#$'! <>! ?#<$-! <-'! 2-#I'! >)! <-'!
.'0#=;!
!
N-'!0#((2!>)!<-'!.'0#=! #='! $>#<'+!01<-!#!<-1*!?'<#(!)1(?! 0-'*!?#*B)#$<B='+;!N-12!
2'=3'2!<>!%''I!>B<!1*)=#='+!=#+1#<1>*;!P*!<-12!+'21:*!<-'!?'<#(!)1(?!#(2>!2'=3'2!#2!<-'!
0#((2!>)!#!?1$=>0#3'!0#3':B1+'!<>!$>*)1*'!<-'!G(#$%!G>+H!=#+1#<1>*!)=>?!<-'!(1FB1+!
*1<=>:'*! $>>('+! ?1$=>0#3'! #G2>=G'=;! 9++1<1>*#((H4! <-'! I=>)'221>*#(! +'21:*! -#2!
*B?'=>B2! <-1*! )1(?! 01*+>02! <>! %''I! ?>12<! #1=! )=>?! '*<'=1*:! <-'! $#31<H;! N-'!
01*+>02!#='!*'$'22#=H!G'$#B2'!1*!I=>)'221>*#(!>G2'=3#<1>*2!>*'!?#H!?#1*<#1*!<-12!
$>*)1:B=#<1>*!)>=!JV!->B=2!>=!?>='!0-1('!)1(('+!01<-!(1FB1+!-'(1B?;!P!-#3'!)>B*+!<-#<!
2(>0!'3#I>=#<1>*!>)!+=H!*1<=>:'*!)=>?!<-'!G#<-!12!2B))1$1'*<!<>!I=>31+'!0#<'=!3#I>=!
)=''!>I'=#<1>*!01<->B<!01*+>02!)>=!#*!->B=4!(>*:!'*>B:-!)>=!?H!+#<#!=B*2;!!
!!
II.c.#Microwave#Receiver#
N-'! ?1$=>0#3'! ='$'13'=! B2'2! <-'! ->=*! #*<'**#! )''+! )=>?! #! Ng! +12-! *'<0>=%!
='$'13'=;! P! +>! *><! B2'!<-'! I#=#G>(1$! +12-! GB<! B2'! <-'! 2?#((! ->=*! #*<'**#! )''+! #*+!
#22>$1#<'+!'('$<=>*1$2;!92!?'*<1>*'+!'#=(1'=4!<-'!+12-!#*<'**#!$>*)1:B=#<1>*!12!?>='!
2B2$'I<1G('! <>! 2<=#H! *>12'! <-#*! #! ->=*! #*<'**#! #(>*';! N-'! #*<'**#! )''+! ?>+B('!
='$'13'2! 1*! <-'! =#*:'! >)! QR;K! YQQ;K! &SO;! N-'! ?>+B('! 12! $#(('+! #! a>0! 5>12'! /(>$%!
Ca5/D!#*+!$#*!G'!IB=$-#2'+!>*!'/#H!)>=!#2!(1<<('!#2!h!L!'#$-;!A>2<!`Y/#*+!a5/2!#='!
>)! 2BG2<#*<1#((H! <-'! 2#?'! +'21:*;! N-'H! $>?I=12'! #! Jf! +1#?'<'=! ?1$=>0#3'! ->=*!
#*<'**#! )''+1*:! #! $1=$B1<! G>#=+! 1*! #! $#2<! #(B?1*B?! ->B21*:;! N-'! $1=$B1<! G>#=+!
$>*<#1*2!#!(>0!*>12'!I='#?I(1)1'=!#*+!bX!?1E'=!$1=$B1<!<>!2-1)<!<-'!)='FB'*$H!>)!<-'!
='$'13'=!<>!<-'!Q!Y!J!&SO!!"#$%&$'!(#$)*%$+,$"-.)/012)=#*:'!0-'='!1<!12!<=#*2?1<<'+!
<-=>B:-!#!$#G('!<>!<-'!Ng!='$'13'=!1*!<-'!->B2';!P*!<-12!2H2<'?!the#receiver#is# tuned#
to"10.75"GHz"by"the"choice"of" a!1" GHz" IF!filter'with'a'50' MHz' bandwidth.!The!total%
noise& power& in& the& 50& MHz# bandpass# is# read% on% a% Hewlett% Packard% HPY432A!RF!
power&meter.!
!
There% are% numerous' other' configurations,!which!could& be& used,& such& as& a&
commercial)10!GHz$ communications* receiver.'Also,' the'IF'section'could'be'replaced'
by# a# software# defined# receiver# with!a" noise!power& measurement!algorithm.!The$
most% important% performance% criterion% for% the% detector$ system$ is$ linearity.& As&
discussed'earlier'in'this' paper,"the" radiometer"works"on"the" linear" extrapolation"of"
the$ temperature$ calibration$ response.$ $ Keep$ in$ mind$ that$ most$ commercial& and&
amateur'equipment'use!an!Automatic%Gain%Control%(AGC)%circuit%to%keep#the#output#
constant'in!spite&of&signal&strength(changes.)This) circuit)must)be)disabled)for)use)in)
this%application.!
!
II.d.#Horn#Antenna!
N-'! Jf! ->=*! #*<'**#! I=>31+'+! 01<-! <-'! a5/! 12! +'21:*'+! #2! #! )''+! ->=*! )>=! <-'!
I#=#G>(1$!+12-;!X>=!<-12!#II(1$#<1>*4!1<!-#2!#!3'=H!G=>#+!G'#?!01+<-!>)!K[!+':=''2;!P!
-#3'!#++'+!#*!'E<'*21>*!->=*!<>!<-'!>=1:1*#(!Jf!+1#?'<'=!->=*!<>!*#==>0!<-'!G'#?!
01+<-!<>!#!QR!+':=''!)1'(+!>)!31'0;!N-12!?#%'2!1<!I>221G('!<>!I>1*<!#<!<-'!2%H!01<->B<!
1*<'=)'='*$'! )=>?! 2B==>B*+1*:! <=''2! #*+! GB1(+1*:2;! 9! *#==>0! G'#?01+<-! 12! #(2>!
='FB1='+!GH!<-'!I=>$'+B='!<>!+'<'=?1*'!#<?>2I-'=1$!'?1221>*!GH!?'#2B=1*:!NC8%HD!
#<!+1))'='*<!'('3#<1>*2;!!
!
!
!
X1:B='!V!N-'!$>*)1:B=#<1>*!>)!<-'!'E<'*21>*!->=*!#*<'**#!#2!1<!#<<#$-'2!<>!<-'!'*+!>)!
<-'!2?#((!->=*!>*!<-'!a5/!
!
N-'! 'E<'*21>*! ->=*! 12! 2->0*! 1*! X1:B='! V;! P<! 12! )#G=1$#<'+! )=>?!;RQRi! 2-''<! G=#22!
)>=?'+! 1*<>! #! $>*'!01<-! #! J;Rf! +1#?'<'=! >I'*1*:! #<! <-'! 2?#(('=! '*+! #*+! #! W;Rf!
>I'*1*:!#<! <-'! (#=:'=! '*+;! N-'! $>*'! 12! U;Rf! (>*:;! N-12! 12! #*! >I<1?B?! ->=*!
$>*)1:B=#<1>*! )>=! #! QR! +':=''! G'#?01+<-! C9G>2'=0#(! #*+! /#(#*12! JRQLD;! N-'!
2<#=<1*:!I#<<'=*!12!$B<!)=>?!2-''<!G=#224!2''!000;$?=I;$>?j$>*'Y$#($B(#<>=;!
!
II.e.#Atmospheric#Emission#
T-'*!I>1*<1*:!#<!<-'! @A/! <-=>B:-!<-'!#<?>2I-'='4! 0'! #(2>!='$'13'!<-'!:(>0! )=>?!
#<?>2I-'=1$!:#22'2!#++'+!<>!<-'!2%H!<'?I'=#<B=';!N-'!'?1221>*!12!I=1*$1I#((H!)=>?!
>EH:'*! #*+! 0#<'=! 3#I>=;! N-12! I-'*>?'*>*! -#2! G''*! 2<B+1'+! GH! #2<=>*>?'=2!!
C/'=2#*'((1!'<!#(;!QUU[D4!#*+!#(2>!'E<'*213'(H!GH!<-'!#<?>2I-'=1$!2$1'*$'!$>??B*1<H!
C"#*22'*4! QUULD4! 0-'='! <-12! '?1221>*! 12! B2'+! <>! ='?><'(H! 2'*2'! $>*+1<1>*2! 1*! <-'!
#<?>2I-'=';! N-'! :(>0! $>=='2I>*+2! <>! #! G=1:-<*'22! <'?I'=#<B='! #<! QR! &SO! #<! 2'#!
('3'(! >)! #II=>E1?#<'(H! [! M! <>! Q[! M4! +'I'*+1*:! >*! <-'! ('3'(! >)! ?>12<B='! #*+! $(>B+!
$>3'=;!!,=>)'221>*#(!#2<=>*>?'=2! -#3'! <-'! #+3#*<#:'! >)!>G2'=31*:!)=>?!G#((>>*2!>=!
)=>?! 2I#$'! 0-'='! <-12! $>=='$<1>*! 12! *':(1:1G(';! P<! 12! #! 2BG2<#*<1#(! $>=='$<1>*4!
->0'3'=4!)>=!#?#<'B=2!0->!I=1*$1I#((H!>G2'=3'!#<!2'#!('3'(;!N-'!21<B#<1>*!:'<2!G'<<'=!
#<! -1:-'=! #(<1<B+'2;! 9<! QJ4RRR! )''<! <-'! #<?>2I-'=1$! *>12'! 12! #G>B<! Q! M! #<! QR! &SO!
C/'=2#*'((1!'<!#(;!QUU[D;!
!
P*!>B=!$#2'!#<?>2I-'=1$!*>12'!#++2!(1*'#=(H!<>!<-'!@A/;!
!
!!!!NC8%HD!!c!NC@A/D!d!NC9<?D! ! ! ! CLD!
!
T'!$#*!2'I#=#<'!<-'!<0>!$>?I>*'*<2!GH!?'#2B=1*:!NC8%HD!#<!<-'!O'*1<-!#*+!#<!('#2<!
>*'! #++1<1>*#(! #*:(';! N-12! $#*! G'! +>*'! G'$#B2'! >)! <-'! :'>?'<=1$! ='(#<1>*2-1I!
G'<0''*!<-'!I>0'=!+'<'$<'+!#*+!<-'!('*:<-!>)!<-'!I#<-;!!
!
#
#
!
X1:B='![!9!+1#:=#?!2->01*:!<-'!='(#<1>*2-1I!G'<0''*!#1=!?#22!#*+!>G2'=31*:!#*:('!
!
X1:B='![!2->02!<-'!I#<-!('*:<-!1*!<-'!#<?>2I-'='!#2!#!)B*$<1>*!>)!>G2'=3#<1>*!#*:(';!
T'!$#*!2''!<-#<!<-12!I#<-!('*:<-4!$#(('+!<-'!#1=!?#224!12!='(#<'+!GH!<-'!)#$<>=!8'$!θ #2!
2->0*!1*!kFB#<1>*!V!G'(>0;!
!
!!!!aCθD!c!aCRD!8'$!θ (4)!!
!
T-'='!aCRD!12!<-'!I#<-!('*:<-!<-=>B:-!<-'!#<?>2I-'='!#<!<-'!O'*1<-!#*+!aCθD!12!<-'!
I#<-!('*:<-! #<! <-'! >G2'=31*:! #*:('! θ;! P*! <-'! b#('1:-Y"'#*2! #II=>E1?#<1>*! <-'!
>G2'=3'+!<'?I'=#<B='!:=>02!(1*'#=(H!01<-!#1=?#22!#2!2->0*!1*!kFB#<1>*![;!
!
! ! ! ! NC9<?4!θ) = NC9<?4!RD!8'$!θ (5)
T-'='! NC9<?4! 0)! 12! <-'! #<?>2I-'=1$! $>?I>*'*<! >)! <-'! >G2'=3'+! <'?I'=#<B='!
?'#2B='+!)=>?!<-'!2%H!#<!<-'!O'*1<-4!#*+!NC9<?4!θ)!12!<-'!#<?>2I-'=1$!$>?I>*'*<!>)!
<-'!>G2'=3'+!<'?I'=#<B='! ?'#2B='+! )=>?!<-'!2%H! #<! #*:('!θ. X=>?!kF;! L!#*+!kF;![!
0'!$#*!+'=13'!#!='(#<1>*!'EI='221*:!<-'!$>*<=1GB<1>*!<>!NC8%HD!)=>?!NC9<?D!2->0*!
1*!kF;!W!G'(>0;!A'#2B='?'*<2!$#*!G'!?#+'!#<!#!*B?G'=!>)!#*:('2!#*+!$>?G1*'+;!
!!!!
NC9<?4!RD!c!lNC8%H4!θ) − Τ(8%H4!RDm!@>2!θ (6)!
Zenith
L(0)
L(e)
e
!
III.#Method#
N-'2'! ?'#2B='?'*<2! ?B2<! G'! I'=)>=?'+! 01<-! #! $>?I('<'(H! B*>G2<=B$<'+! 31'0! >)!
<-'!2%H;!N=''2!#*+!><-'=!>Gn'$<2!<-'=?#((H!=#+1#<'!#<!<-'!#?G1'*<!<'?I'=#<B='!>)!<-'!
'*31=>*?'*<! $#B21*:! 2BG2<#*<1#(!'==>=2;! N-'='! 12! *>! *''+! <>! I'=)>=?! <-'2'!
?'#2B='?'*<2!1*!+#=%*'22;! 6>B!+>! *''+!<>!#3>1+! I>1*<1*:!<-'!#*<'**#! <>0#=+!<-'!
2>B<-!0-'='!Ng!2#<'((1<'2!#='!<=#*2?1<<1*:!*'#=!<-'!='$'13'=!G#*+I#22;!!
!
N-'! I=>$'+B='! 12! 21?I(';! N-'! <><#(! ?1$=>0#3'! I>0'=! '?1<<'+! )=>?! <-'! KKM! $>(+!
(>#+4!#*!#?G1'*<!<'?I'=#<B='!G(#$%!G>+H!=#+1#<>=!#*+!<-'!2%H!?B2<!G'!?'#2B='+!1*!
2'FB'*$';!N-12!2'FB'*$'!12!2->0*!1*!<-'!I-><>:=#I-2!1*!X1:B='!W;!!
!
!
!
!
!
X1:B='!W;!8'FB'*$'!>)!#*<'**#!I>21<1>*2!#*+! 2>B=$'2!)>=! $#(1G=#<1*:!<-'!=#+1>?'<'=!
9;!9?G1'*<!<'?I'=#<B='!#G2>=G'=!?>B*<'+!#<!<-'!'*+!>)!<-'!?1$=>0#3'!->=*!
/;!S>=*!#*<'**#!#1?'+!1*<>!<-'!$>(+!(>#+!2>B=$'!#<!KKM!
@;!S>=*!#*<'**#!#1?'+!#<!<-'!O'*1<-!
!
N-'!'('$<=>*1$2!1*! I=>)'221>*#(!'FB1I?'*<!#='! <-'=?>2<#<1$#((H!$>*<=>(('+;!P! +>!*><!
2<#G1(1O'! <-'! <'?I'=#<B='! >)! ?H! 'FB1I?'*<;! P! 0#=?! BI! ?H! 'FB1I?'*<! )>=! #<! ('#2<!
>*'!->B=!#*+!<=H!<>!'E'$B<'!<-'!?'#2B='?'*<!FB1$%(H;!P!<=H!<>!#3>1+!<1?'2!0-'*!<-'!
#?G1'*<!<'?I'=#<B='!12!$-#*:1*:!=#I1+(H;!!
!
N-'! 1*IB<! <>! <-'! S'0('<<! ,#$%#=+! I>0'=! ?'<'=! 12! ='2'<! <>! O'=>! G')>='! '#$-!
?'#2B='?'*<;!N-'!2<#G1(1<H!>)!<-'!KK!M!I>0'=!='#+1*:!12!#!?'#2B='!>)!<-'!2<#G1(1<H!>)!
<-'! '*<1='! 2H2<'?!#2! <-'! G>1(1*:! I>1*<! >)! *1<=>:'*! 12! $>*2<#*<;! P! )1*+! <-#<! <-'! <><#(!
I>0'=!='#+1*:!12!2<#G('!<>!Qo!>3'=!<-'!$>B=2'!>)!#!>*'!->B=!+#<#!=B*;!
!
IV.#Results#
N-'!#*#(H212!>)!<-'! +#<#!#*+!<-'!+'<'=?1*#<1>*! >)!<-'!?'#2B='+!@A/! =#+1#<1>*!#='!
G'2<!B*+'=2<>>+! :=#I-1$#((H;! T'! $#*! $>*2<=B$<! #! :=#I-!>)! ?1$=>0#3'! *>12'! I>0'=!
3'=2B2!2>B=$'!<'?I'=#<B='!#2!2->0*!1*!X1:B='!K!G'(>0;!
!
!"#$%&'()#*"$&+,%&%-&./01&#23&441&5#6,7*#8-2&9#%#&
:&;&<=<<<0>&?&<=<@A/&
!"!!!!#
!"!$!!#
!"%!!!#
!"%$!!#
!"&!!!#
!"&$!!#
!"!# $!"!# %!!"!# %$!"!# &!!"!# &$!"!# '!!"!# '$!"!#
BCD'E&FCGEH&IG&
JEKFEHLJMHE&&&1"6N,2$&
5L!DOHLJDCB&LB9&JEKFEHLJMHE&9EJEHKDBLJDCB&
!
!
X1:B='!K;!9!:=#I-1$#(!='I='2'*<#<1>*!>)!<-'!?'#2B='?'*<!>)!NC8%HD!>*!<-'!G#212!>)!#!
<0>Y<'?I'=#<B='!$#(1G=#<1>*!>)!#!?1$=>0#3'!=#+1>?'<'=;!
!
N-'! *>12'! I>0'=! +#<#! #<! eJUWM! C=>>?! <'?I'=#<B='D! #*+! KKM! Ca1FB1+! *1<=>:'*!
<'?I'=#<B='D! #='! ('#2<! 2FB#='2! )1<<'+! <>! #! (1*';! N-'! 3#(B'! >)! ?'#2B='+! 2%H! *>12'!
I>0'=!12!<-'*!I(><<'+!>*!<-'!$#(1G=#<1>*!(1*';!N-'!3#(B'!>)!<-'!<'?I'=#<B='!>)!<-'!2%H!
12!='#+!>))!>)!<-'!EY#E12;!6>B!$#*!$('#=(H!2''!<-'!#+3#*<#:'!>)!B21*:!(1FB1+!S'(1B?!)>=!
<-'! $>(+! <'?I'=#<B='! $#(1G=#<1>*! )=>?! <-'! :=#I-;! N-'='! 12! #! 2BG2<#*<1#(!
'E<=#I>(#<1>*!)=>?!KKM!<>!NC8%HD;!
!
^*!<-12!=B*! ?'#2B='+!2%H!<'?I'=#<B='! 0#2! $#($B(#<'+!)=>?! <-12! +#<#!#*+! )>B*+! <>!
G'!Z;U!M;!X>=! #! $('#=!2%H!<-'!$>=='$<1>*! )>=!<-'!QR!&SO! '?1221>*! >)!<-'!#<?>2I-'='!
0#2![;R!M;!N-'!?'#2B='+!NC@A/D!124!
!
!NC@A/D!c!NC8%HD!_!NC9<?D!c!Z;UM!_![;RM!c!L;UM!!!CKD!
!
N-'!#$$'I<'+!NC@A/D!c!J;KLM!12!$(>2'!<>!<-'!?'#2B='+!<'?I'=#<B='!>)!L;UM;!b'2B(<2!
3#=H!)>=!NC@A/D!)=>?!RM!_![M!
#
V.#Discussion#
P<! 12! ?H! ->I'! <-#<! #?#<'B=2! 01((! <=H! <>! +BI(1$#<'! <-'2'! ?'#2B='?'*<2;! N-'!
I=>$'+B='2!+12$B22'+!-'='! #='!*><!<-#<! +1))1$B(<;!^(+'=4! #*#(>:! 1*2<=B?'*<2!2B$-! #2!
<-'!S,VLJ9!I>0'=!?'<'=!#='!2B1<#G('!)>=!<-'2'!?'#2B='?'*<24!#*+!#='!?>+'=#<'(H!
I=1$'+! >*! 'G#H;! P<! 12! #(2>! '#21(H! I>221G('! <>! #+#I<! #! 78/! +>*:('! 2>)<0#='! +')1*'+!
=#+1>!C8.bD!#2!<-'!PX!#?I(1)1'=!#*+!+'<'$<>=4!<->B:-!>*'! 2->B(+!$-'$%! <-'!(1*'#=1<H!
>)!<-'!='2I>*2';!!
!
P!)''(!<-#<!01<-!$#='!1<!12!I>221G('!<>!='I=>+B$1G(H!>G<#1*!<-'!3#(B'!>)!<-'!<'?I'=#<B='!
>)! <-'! @A/! 01<-1*! QM! GB<! 1<! 01((! ='FB1='! 2>?'! 1?I=>3'?'*<2;! P! $#*! 2''! <-#<!
<'?I'=#<B='!2<#G1(1O#<1>*!>)!<-'!'('$<=>*1$2!01((!I=>G#G(H!G'!*'$'22#=H;!9(2>4!<-'='!12!
#! I=>G('?! 1*! <-'! $>*)1:B=#<1>*! >)! <-'! $>(+! (>#+;! N-'='! 12! #! $-#*:'! >)! 1*+'E! >)!
=')=#$<1>*!#<! <-'!2B=)#$'! >)! <-'!(1FB1+! *1<=>:'*!#1=! 1*<'=)#$'4! 0-1$-!$#B2'2! 2<#*+1*:!
0#3'2!>)! ! djY! Jo! 1*!I>0'=! ('3'(! 1*! <-'! $#31<H;!P! #?! 'EI'=1?'*<1*:! 01<-! <1(<1*:!<-'!
.'0#=!<>!$#B2'!<-'!(1FB1+!*1<=>:'*!2B=)#$'!<>!G'!#<!#*!#*:('!<>!<-'!->=*!#*<'**#!#E12;!
N-12!#II'#=2!<>!#(('31#<'!<-'!I=>G('?!GB<!*''+2!2>?'!)B=<-'=!0>=%;!
#
VI.#References!
/'*2#+>B*4!'<!#(;4!9!a1FB1+YS'(1B?Y@>>('+!#G2>(B<'!=')'='*$'!$>(+!(>#+!)>=!(>*:Y
0#3'('*:<-!=#+1>?'<=1$!$#(1G=#<1>*4!b'31'0!>)!8$1'*<1)1$!P*2<=B?'*<24!WL4!VLKKY
VLZU!C^$<>G'=!QUUJD!!
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A Measurement of the Temperature of the Cosmic MicrowaveBackground at a Frequency of 7.5 GHz
Article
Full-text available
  • May 1990
We have measured the intensity of the cosmic microwave background (CMB) at a frequency of 7.5 GHz (wavelength 4.0 cm) using a ground-based, total power radiometer calibrated at the horn aperture by an external cryogenic reference target. The radiometer measured the difference in antenna temperature between the reference target and the zenith sky from a dry, high-altitude site. Subtraction of foreground signals (primarily atmospheric and galactic emission) measured with the same instrument leaves the CMB as the residual. The radiometer measured the atmospheric antenna temperature by correlating the signal change with the airmass in the beam during tip scans. The small galactic signal was subtracted based on extrapolation from lower frequencies, and was checked by differential drift scans. The limiting uncertainty in the CMB measurement was the effect of ground radiation in the antenna sidelobes during atmospheric measurements. The thermodynamic temperature of the CMB at 7.5 GHz is 2.59 {+-} 0.07 K (68% confidence level).
CMB Telescopes and Optical Systems To appear in: Planets, Stars and Stellar Systems (PSSS) Volume 1: Telescopes and Instrumentation
Article
Full-text available
The cosmic microwave background radiation (CMB) is now firmly established as a fundamen-tal and essential probe of the geometry, constituents, and birth of the observable Universe. The CMB is a potent observable because it can be measured with precision and accuracy. Just as importantly, theoretical models of the Universe can predict the characteristics of the CMB to high accuracy, and those predictions can be directly compared to observations. There are multiple aspects associated with making a precise measurement. In this review, we focus on optical components for the instrumentation used to measure the CMB polariza-tion and temperature anisotropy. We begin with an overview of general considerations for CMB observations and discuss common concepts used in the community. We next consider a variety of alternatives available for a designer of a CMB telescope. Our discussion is guided by the ground and balloon-based instruments that have been implemented over the years. In the same vein, we compare the arc-minute resolution Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT). CMB interferometers are presented briefly. We con-clude with a comparison of the four CMB satellites, Relikt, COBE, WMAP, and Planck, to demonstrate a remarkable evolution in design, sensitivity, resolution, and complexity over the past thirty years.
A measurement of the cosmic microwave background temperature at 7. 5 GHz
Article
Full-text available
  • Sep 1992
The temperature of the cosmic microwave background (CMB) radiation at a frequency of 7.5 GHz (4 cm wavelength) is measured, obtaining a brightness temperature of T(CMB) = 2.70 +/- 0.08 K (68 percent confidence level). The measurement was made from a site near the geographical South Pole during the austral spring of 1989 and was part of an international collaboration to measure the CMB spectrum at low frequencies with a variety of radiometers from several different sites. This recent result is in agreement with the 1988 measurement at the same frequency, which was made from a different site with significantly different systematic errors. The combined result of the 1988 and 1989 measurements is 2.64 +/- 0.06 K. 11 refs.
The Temperature of the Cosmic Microwave Background Radiation at a Frequency of 10 GHz: Erratum
Article
Full-text available
  • Jan 1988
We have measured the temperature of the cosmic microwave background radiation (CMBR) at a frequency of 10 GHz (wavelength 3.0 cm) as part of a larger effort to determine the spectrum of the CMBR in the Rayleigh-Jeans region. The instrument used is a superheterodyne Dicke-switched radiometer. We have repeated the measurement over four summers with successively improved techniques and equipment. Our best estimate of the CMBR thermodynamic temperature at 10 GHz is 2.61 ± 0.06 K, where the error estimate is a 68% confidence level limit.
Effects of Atmospheric Emission on Ground-based Microwave Background Measurements
Article
Full-text available
  • Jun 1995
We present an analysis of multifrequency measurements of atmospheric emission in the Rayleigh-Jeans portion of the cosmic microwave background spectrum (1-90 GHz) taken since 1986 from White Mountain, CA, and from the South Pole. Correlations of simultaneous data at 10 and 90 GHz and accurate low-frequency measurements show good agreement with model predictions for both sites. Our data from the South Pole 1989 campaign combined with real-time measurements of the local atmospheric profiles provide accurate verification of the expected independent contributions of H2O and O2 emission. We show that variations on the order of 10% of the oxygen emission (both resonant and nonresonant components) are present on timescales of hours to days, mainly due to the evolution of the atmospheric pressure profile. Oxygen emission fluctuations appear larger than previously expected and may have significant consequences for ground-based cosmic microwave background experiments.
Atmospheric Remote Sensing by Microwave Radiometry
Chapter
Full-text available
  • Jan 1993
A liquid‐helium‐cooled absolute reference cold load for long‐wavelength radiometric calibration
Article
  • Nov 1992
We describe a large (78 cm) diameter liquid‐helium‐cooled blackbody absolute reference cold load for the calibration of microwave radiometers. The load provides an absolute calibration near the liquid‐helium (LHe) boiling point, with total uncertainty in the radiometric temperature of less than 30 mK over the 2.5–23‐cm wavelength (12–1.3 GHz) operating range. Emission from those parts of the cold load not immersed in LHe is ≤25 mK and the reflection coefficient is ≤3.5×10<sup>-4</sup>. This cold load has been used at several wavelengths at the South Pole, Antarctica and at the White Mountain Research Station, California to calibrate spectral measurements of the cosmic microwave background radiation. For the instruments operated at 20‐, 12‐, 7.9‐, and 4.0‐cm wavelength at the South Pole, the total corrections to the LHe boiling‐point temperature (∼3.8 K) were 48±23, 18±10, 10±18, and 15±16 mK, respectively. In operation, the average LHe loss rate was ≤4.4 l/h, allowing day‐long periods of operation without a LHe fill. The boiloff rate is not strongly dependent on the radiative load at the aperture, yielding very stable operation and radiometric performance. Design considerations, radiometric and thermal performance, and operational aspects are discussed. A comparison with other LHe‐cooled reference loads including the predecessor of this cold load is given.
The Measurement of Thermal Radiation at Microwave Frequencies
Article
  • Jul 1946
The connection between Johnson noise and blackbody radiation is discussed, using a simple thermodynamic model. A microwave radiometer is described together with its theory of operation. The experimentally measured root mean square fluctuation of the output meter of a microwave radiometer (0.4°C) compares favorably with a theoretical value of 0.46°C. With an r-f band width of 16 mc/sec., the 0.4°C corresponds to a minimum detectable power of 10−16 watt. The method of calibrating using a variable temperature resistive load is described.
How to Measure the Cosmic Microwave Background with TV Satellite Equipment (2015) Stein and Forster summary in English
  • Koppen
Koppen, How to Measure the Cosmic Microwave Background with TV Satellite Equipment (2015) Stein and Forster summary in English. portia.astrophysik.uni--kiel.de/~koeppen/CMB.pdf
  • Jul 2008
  • 84-90
  • Forster Stein
  • Kosmologie Mit Kaninchendraht Und Wasser
Stein and Forster, Kosmologie mit Kaninchendraht und Wasser (Cosmology with Rabbitwire and Water), Sterne und Weltraum, 84--90 (July 2008)