Project Cyclops, A Design... - Department of Earth and Planetary ...

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shownasa roomtemperatureMESFET(Metalgate Schottkybarrierfield-effect transistor) amplifier.Alternatively,parametric down-converters followedbyparametricamplifiersalloperating in the20° Kenvironment mightofferbettergainstabilityandgoodnoiseperformance. A fixedfrequency localoscillator signalsynthesized fromthestandardreference frequencies isneededfor thedownconversion. Fetritephaseshiftersprogrammed by thecentralcomputerareusedto shiftthephaseof thislocaloscillatorat eachantennato providebeam steeringandtrackingcapability. Further discussion of the phase shifter is given in Appendix J. Using the receiver system described above, the estimated system noise temperature would vary from about 40 ° K at 500 MHz to about 24 ° K at 3 GHz. The receiver noise and waveguide loss decrease with frequency but the spillover loss and sky temperature increase at lower frequencies. The minimum noise temperature is expected to occur around 1.5 GHz and to be about 20° K. be undertaken using the Cyclops array, good frequency stability is essential. The best frequency standard available today is the hydrogen maser phase locked to a high quality crystal oscillator (refs. 13-15). Table 9-1 is a comparison of several state-of-the-art frequency standards. Figure 9-11 shows the spectr',d purity obtainable from the major kinds of frequency standards. The ordinate is the rms frequency deviation divided by the operating frequency, while the abscissa is the averaging time over which the measurement of Afrms is made. The hydrogen maser gives the best performance for all averaging times and, for times on the order of 100 seconds, which are involved in the Cyclops signal processing, the hydrogen maser is some 30 times better than a rubidium maser and some 500 times better than cesium. Hydrogen masers are not commercially available at present, but several have been built by Varian Associates, by the Smithsonian Astrophysical Observatory, and by others. I0 -9 "T • l I THE LOCAL OSCILLATOR SYSTEM The three major functional components of the Cyclops local oscillator system shown in Figure 9-1 are the primary frequency standard, the distribution system, and the frequency synthesis and phasing systems located at each antenna. In principle, one could generate centrally the local oscillator frequencies needed for reception of a particular band rather than synthesizing them at each antenna. However, it does not appear practical to transmit frequencies over a large frequency range to the individual antennas and maintain the phase tolerances required. For this reason only two precise frequencies are generated centrally and distributed, and the synthesis is done locally at each antenna. In a system the size of Cyclops with its thousand or more antenna elements, the cost of any item associated with each antenna must be kept low, and the cost of transmission circuits is quite appreciable. However, the cost of a single item such as the central frequency standard is an insignificant part of the total system cost, and to the extent that increased expense in this item will improve system performance it is easily justifiable. The spectral purity of the central frequency standard limits the minimum bandwidth that can be used in the signal processing, which in turn is directly related to the minimum detectable signal strength. Since the detection of very weak signals is the whole object of building so large an array, only frequency standards of the highest possible spectral purity and stability should be considered. Also, if very long base-line interferometry is to Af _- rms Figure 9-11. ,o-'°_-_'__ Rb,QUART_ i i0-II i0-12 _ _" _ _'_,_, _ ARTZ 10-14 L , 10-15 _ 1 . _L k • 5 ,o-4 ,o-2 ,o-O _oz ,04 Io6 AVERAGING TIME, sec Fractional frequency fluctuation versus averaging time. Since the reliability of the hydrogen maser, as with any other device, is not perfect, and since the entire Cyclops array would be inoperative if the frequency standard were to fail, at least two hydrogen masers should be provided. In fact, if two standards disagree, a third is needed to determine which of the two is in trouble, so it is recommended that the control center include three hydrogen masers. The standard lrequency distribution system must distribute the reference frequencies required to synthesize all local oscillator and pilot frequencies at each antenna site with an unambiguous phase relationship. This requires that one of the standard frequencies be equal to the smallest desired tuning increment, for the following reason. The usual frequency synthesizer contains frequency dividers as well as multipliers and mixers. Any frequency divider that divides a reference 96
TABLk ?- I A COMPARISON OF VARIOUS PRI'£1SION FREQUENCY SOUR('IzS 7),pc ,JJ tlydrogen maser plus Passive ('s Passive Rb 5-Mttz cryslal sigJtal s_urc(" pllase-locked oscillalor ,4remit tkam wiper cell oscillator I,ong-ternt stability Not delectable (less Nol deteciable (tess Less lhan two Less than five (mapfftude than two parts in than lwo parts in parts in 1(] I _ parts in I(P" rtfdri]/) i012 per year) i012 pet year) per month per day Flicker level offractimtal Probably less than Probably less than 3.6X 10 -t _ IX IO -_ ' jt'equen O, 1X 10- i a I X 10 -I _ Jluctuatkm Weight (lh) 600 60 37 I. I Volume h'u ft) 16.4 I .3X ?)3 .()2'_ Power requirement 200 43, ac or 48, ac or 4 (W) 27,dc 35, dc (b.st Not available commer- (dollars) cially aI present lime 14,800 7,500 c)50 Unusual Best phase spectral ttigh intrinsic Least expensive Low cost. high fi, atures density accuracy and atomic signal source reliability reproducibility: second is defined by the cesium O.0 transition Alagnittde oJ Less than one part Less than five I,ess lhan five Less than 2.5 ambient in IfP _
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(NASA-CR- 11_5) PROJECT CYCLOPS: A
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CR 114445 Available to the public A
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At this very minute, with almost ab
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ACKNOWLEDGMENTS The Cyclops study w
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COMMUNICATION BY ELECTROMAGNETIC WA
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APPENDIX A - Astronomical Data ....
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t _ 2
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of the living beings evolved by the
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Figure2-1. M3I,the great galaxy in
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self.Thus,wecaninterpretFigure2-2as
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magnitude (low brightness) end, the
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Red Giant. The transition from main
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tion, as the central part of the cl
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TABLE 2-4 SELECTED NEARBY STARS WIT
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tideraisingforcesasr--_ where ,v =
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3. Is it possible that living syste
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lawsof natural selection, more like
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starsthroughout the Galaxyhave also
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if the longevity of that life is ty
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The imaginative reader will have no
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Lookingfar ahead,supposewe aresucce
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usuallyterritorial expansion by the
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IOO IO 1 [ [ J [ J I J i [ i I i I
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order with what Morrison has descri
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The quantity gtPt is often called t
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which might result from synchronous
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1. Wewillnothavenough resolving pow
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normalwith the meanat o x/--2. When
Page 58 and 59: Chapter11 in analyzingthe dataproce
Page 60 and 61: Therangelimitisthenfoundbyequating_
Page 62 and 63: TABLE 5-3 PARAMETER Wavelength Tran
Page 64 and 65: angeanddirectlyasthesquareof antenn
Page 66 and 67: "_ i i i i i p = STELLAR DENSITY AT
Page 68 and 69: I-- g u. O >- I--- .d tit (]O 0 0.
Page 70 and 71: andwidth that will still give near
Page 72 and 73: acquisitionphasefor otherraces.Supp
Page 74 and 75: 1. They would transmit continuously
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Page 79 and 80: vz .i g)mo PAGE NOr Ir[[,MZ 7. THE
Page 81 and 82: The price of incomplete sky coverag
Page 83 and 84: modest size.A largedatabaseontapeor
Page 85 and 86: THEAUXILIARYOPTICALSYSTEM Althoughn
Page 88 and 89: edetectedat 20,000light-years byCyc
Page 90 and 91: feeds must correct for spherical ab
Page 92 and 93: side of the dish and shade on the o
Page 94 and 95: TABLE 8-1 UNADJUSTED UNIT COST DATA
Page 96 and 97: 7. Using huge specially designed ji
Page 99 and 100: 9. THE RECEIVER SYSTEM The receiver
Page 101 and 102: whereP is the radiated power. Divid
Page 103 and 104: SHADOWED AREA SHADOWED AREA // // /
Page 105 and 106: Corrugatedhornssupportingbalancedhy
Page 107: o 50 ----- - _ T i 20 _,o 5 ,,,5 09
Page 111 and 112: CENTRAL POINT STATION LSB LINE FREQ
Page 113 and 114: A02 .... + No (25) (i C 1 where No
Page 115 and 116: COAXIAL LINE DIRECTIONALCOUPLER FRE
Page 117 and 118: DeJager, J.T.:IEEETrans.onMicrowave
Page 119 and 120: pR_ING PA6E BLANK HOT FILMF_ 10. TR
Page 121 and 122: o-------------o_ _ o o o o ing of t
Page 123 and 124: addedto theother IF channel. The tw
Page 125 and 126: INPUT MHZ _PF 500 MHZ i : 575 T1 92
Page 127 and 128: azimuth _) has a delay (2a/c)sin 0
Page 129 and 130: stripline. For 2 _< k _< 6, appropr
Page 131 and 132: mation are common to all antennas i
Page 133 and 134: A cable pair costs about 20 cents/m
Page 135 and 136: 11. SIGNAL PROCESSING The Cyclops s
Page 137 and 138: 1.0 T t t I I r .9 -8 asynchronousl
Page 139 and 140: collimated coherent light. A simple
Page 141 and 142: power of the film and associated op
Page 143 and 144: samples simultaneously onto the sam
Page 145 and 146: outputs is assumed. COMPOSITE SIGNA
Page 147 and 148: SPECTRUM I n LINES M n LINES U SPEC
Page 149 and 150: signal andyet have a tolerable fals
Page 151 and 152: i --_- i i i i large values of n. T
Page 153 and 154: plottedin Figure11-15for various va
Page 155 and 156: All the1Fsignalswillarrivein phasei
Page 157 and 158: x:(1 +x) x 2 - _ -- (53) If we wish
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3's = unitcostof signal planelectro
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where0ma x is the maximum value of
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Roughestimates of the costs of buil
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12. CYCLOPS AS A BEACON Although th
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13. SEARCH STRATEGY The high direct
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distantgalaxies (oraninertialrefere
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wouldfollowtheuppermost linein Figu
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persquaredegreeof fieldwouldberequi
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starsfrom/'18 to G5 could support a
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14. CYCLOPS AS A RESEARCH TOOL Thro
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Only a few such galaxies have been
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15. CONCLUSIONS AND RECOMMENDATIONS
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perhapsdecadesand possiblycenturies
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APPENDIX A ASTRONOMICAL DATA DISTAN
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PLANETARY Planet ORBITS Semimajor S
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APPENDIX B SUPERCIVILIZATIONS AND C
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ABIOLOGICAL CIVILIZATIONS Many writ
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182
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tqOT APPENDIX C OPTIMUM DETECTION A
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to rmsnoise.Wenotethatthematchedfil
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APPENDIX D SQUARE LAW DETECTION THE
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If the output filter is very wide c
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if B/2 > T we can start instead wit
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Let us now introduce the normalized
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where h-- = expectation count of si
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APPENDIXE RESPONSE OF A GAUSSIAN FI
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APPENDIXF BASE STRUCTURES AZ-EL BAS
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ack,it shouldnotbenecessary to prov
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204
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206 i
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PAGE BLANK NOT APPENDIX H POLARIZAT
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APPENDIX I CASSEGRAINIAN GEOMETRY C
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APPENDIXJ PHASINGOFTHE LOCALOSCILLA
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APPENDIXK EFFECTOF DISPERSION IN CO
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APPENDIX L TUNNEL AND CABLE LENGTHS
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where r = "Ym/'rs- If we let o-_--o
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L-4 we see that the length of IF ca
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APPENDIX M PHASING AND TIME DELAY A
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andobtain V = 2 (Ps [! + _(Ar)] +Pn
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L" D 226
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APPENDIX N SYSTEM CALIBRATION The p
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APPENDIXO THE OPTICAL SPECTRUM ANAL
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232
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APPENDIX P LUMPED CONSTANT DELAY LI
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Thevalueofthefinalcoilonthelineis =
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APPENDIXQ CURVES OF DETECTION STATI
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I I I I LE :E oo
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APPENDIX R RADIO VISIBILITY OF NORM
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io 3 - l rlrllll I I I ]l+,ll_ I _f
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