Conference PaperPDF Available

An Amateur Instrument for the Detection of the Cosmic Microwave Background

Authors:
  • Central Caribbean Marine Institute, Cayman Islands

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.
Content may be subject to copyright.
An#Amateur#Instrument#for#the#Detection#of#the#Cosmic#
Microwave#Background#
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#*<'**#! )''+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^$<>G'=!QUUJD!!
!
/'=2#*'((1!'<!#(;4!k))'$<2!>)!9<?>2I-'=1$!k?1221>*!>*!&=>B*+Y/#2'+!A1$=>0#3'!
/#$%:=>B*+!A'#2B='?'*<24!92<=>I-H21$#(!">B=*#(4!VVZ4!ZYQW!C"B(H!QUU[D!
!
"#*22'*4!9<?>2I-'=1$!8'*21*:!GH!A1$=>0#3'!b#+1>?'<=H4!T1('H!CQUULD!
!
M>:B<4!'<!#(;4!A'#2B='?'*<!>)!<-'!N'?I'=#<B='!>)!<-'!@>2?1$!A1$=>0#3'!
/#$%:=>B*+!#<!#!X='FB'*$H!>)!K;[!&SO4!92<=>I-H21$#(!">B=*#(4!L[[4!QRJYQQL!CA#H!
QUURD!
!
M>:B<4!'<!#(;4!N-'!N'?I'=#<B='!>)!<-'!@>2?1$!A1$=>0#3'!/#$%:=>B*+!b#+1#<1>*!#<!#!
X='FB'*$H!>)!QR!&SO4!92<=>I-H21$#(!">B=*#(4!LJ[4!QYQ[!CX'G!QUZUD!
.1$%'4!N-'!A'#2B='?'*<!>)!N-'=?#(!b#+1#<1>*!#<!A1$=>0#3'!X='FB'*$1'24!b'31'0!>)!
8$1'*<1)1$!P*2<=B?'*<24!QK4!JWZYJK[!C"B(H!QUVWD!!
S#*#*H!'<!#(;4!@A/!N'('2$>I'2!#*+!^I<1$#(!8H2<'?24!I='I=1*<4!<>!#II'#=!1*!,(#*'<24!
8<#=2!#*+!8<'((#=!8H2<'?24!g>(B?'!Q4!N'('2$>I'2!#*+!P*2<=B?'*<#<1>*4!#=`13p!
QJRW;JVRJ3Q!,#:'!U!CJRQVD!
M>II'*4!S>0!<>!A'#2B='!<-'!@>2?1$!A1$=>0#3'!/#$%:=>B*+!01<-!Ng!8#<'((1<'!
kFB1I?'*<!CJRQ[D!8<'1*!#*+!X>=2<'=!2B??#=H!1*!k*:(12-;!!I>=<1#;#2<=>I-H21%;B*1Y
%1'(;+'je%>'II'*j@A/;I+)!
!A1$-'(!,1#<!#<!,#=12!.1+'=><!7*13'=21<H!-#2!G''*!'EI'=1?'*<1*:!01<-!#?#<'B=!2<H('!
'FB1I?'*<;!!
-<<Ipjj000;#I$;B*13YI#=12K;)=jeI1#<jA1$-'(q,1#<2q21<'ja'EI'=1'*$'q,T;-<?(!
8<'1*!#*+!X>=2<'=4!M>2?>(>:1'!?1<!M#*1*$-'*+=#-<!B*+!T#22'=!C@>2?>(>:H!01<-!
b#GG1<01='!#*+!T#<'=D4!8<'=*'!B*+!T'(<=#B?4!ZVYUR!C"B(H!JRRZD!
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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).
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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.
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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.
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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.
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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.
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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.
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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
  • 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)