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

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,,_Td d a a c c b b DISTANCE Figure 10-6. Two inversions and one interchange. --'," NOTRANSPOSITIONS. I I t I the two IF bands without inversion as shown in Figure 10.6. Let 1.; +A 1"3+[4 7=1 - 1 21.o 21.o be the fractional frequency interval from the pilot to the center of each IF band, and let e = lSI -'h'l be the fractional departure of any IF frequency from its band center. Then, for the transmission system depicted in Figure 10-6, a frequency introduced as1.=1.o (I + 3, + e) will be sent one quarter of the distance, converted to 1"o (1 - 3, - e), sent one quarter of the distance, converted to [o (1 + 3, - e), sent one quarter of the distance, converted to 1.o (1 - 3, + e), and sent the remaining quarter of the distance. The total relative normalized loss is therefore 1 P =4 [_/1 +(7+e) + _/1 -(.T+e) + _/1 +('T-e) + x/J - (.T- e) 1 - 1 (8) / \ 3'2 5")'4 e 2 [ 15 ._ 5e 4 8 128 8 8 128 +...---_+--8;- --+.. (8a) Because 3, is constant, only the latter terms in e 2 and e 4 involve variation in transmission across the band. Since only even powers occur, each band is symmetrical about the center, This is to be expected since in Figure 10-6, for example, one observes that each band edge successively occupies all four frequencies/l, J'2, f3, I4. By analogy to the transposition of open-wire lines to avoid crosstalk, we shall refer to this method of obtaining uniform response as transposition equalization. Figure 10-7 shows the relative normalized loss with no transposition, with one midpoint inversion and with two inversions and a band interchange. If ao = 120 dB, i I _2889 A • GNE INVERSION B = TWO INVERSIONS AND ONE L INTERCHANGE 0 I O0 200 300 400 500 Figure 10-7. Effect o1. transposition equalization. we see that with one inversion (,4 curves) both IF bands have a slope of 120 (-0.0116 + 0.0742) = 7.5 dB from the inner to the outer edges. Over a 20 ° C range, this slope would vary by (10/293) 7.5 _ 0.34 dB, which is probably small enough not to require compensation. Also, the equalizers to correct the slope across the band present no serious problem. However, a large level difference between IF bands will accumulate (on the longer lines) before the single inversion at the midpoint. On the longer lines, three (or five) inversions might be necessary. If a midpoint band interchange is used, together with an inversion at the one-quarter and three-quarter points, we see from the B curves that the transmission in each IF band is symmetrical about the band center and is 120(-O.0341 + 0.0429) _ 1 dB greater at the band edges than at the centers. No temperature compensation is needed and the normal rolloffs of the IF amplifiers and filters can be used to flatten the passband to within a tenth of a decibel if desired. If the pilot frequency,fo, lies midway between the two bands-that is, if/o = (]'2 + f3)/2 = (fl +[4)/2, and if 1.3 - f2 = 21.1 -the inversions and interchanges are easily accomplished. (We are assuming that (f2 -fl ) = (/4 -1"3), L 112
INPUT MHZ _PF 500 MHZ i : 575 T1 925 250 X2 8PF MHZ MULT Figure 10-8. Channel inverter. 75 TO425 WHZ i.e., that the two bands are alike.) Figure ]0-8 shows one way of accomplishing the inversion. The 250-MHz pilot is extracted by a narrow band pass filter and multiplied by 2 to obtain a 500-MHz carrier. Using this as the local oscillator (LO) in a first mixer and taking the upper sideband, we translate the entire IF spectrum upward by 500 MHz. Then the same LO signal is applied to a second mixer and the lower sideband is taken as the inverted output. Since the same frequency is used in the up and down conversion, the exact frequency is of no consequence and it may not be necessary to derive the 500-MHz signal from the 250-MHz pilot. However, there may be some advantage in suppressing higher order modulation products to have a particular phase relation between the LO signal and the 250-MHz pilot. Figure 10-9 shows one method of accomplishing the swapping of the IF channels. Here the 250-MHz pilot is extracted and used as the LO frequency for two mixers and is reintroduced into the line through an isolation amplifier. One mixer is supplied with the upper IF band and the lower sideband is taken as the output. The other mixer is supplied with the lower IF band and the upper sideband is taken as the output. The two new IF bands and the pilot are added at the output. ._ 325 TO 425 MHZ BPF BPF 250 "l MHZ 75 TO 175 MHZ ,_ ?5 TO 175 MHZ BPF _25 TO 425 MHZ Figure 10-9. Channel interchanger. In the interchange process, each IF band passes through the same two band pass filters, but in reverse order. Thus, the same delay is added to each band. If desired, the 250-MHz pilot can be shifted in phase by an BPF amount corresponding to this same delay. Then, as in the inverter, the whole IF signal can be considered to have undergone an additional flat delay. !,' For array diameters up to 5 km a satisfactory solution to the IF transmission problem would be to use 7/8-in. diameter coaxial lines and three repeaters per line for all lines. (There are only a few lines so short that this combination would represent overengineering.) Two of the repeaters would be inverting and the middle repeater would interchange bands. Also, repeaters would have a maximum gain of about 30 dB. Automatic gain control would be used to set the level of the 250-MHz pilot at the output of each repeater to a standard level. If the AGC system cannot operate satisfactorily over a 30-dB range, input pads could be switched in on the shorter runs to center the AGC in its proper operating range. In this way all signals arriving at the control center will have undergone (except for total delay) substantially the identical transmission history. For larger arrays, additional pairs of inverting repeaters may be added symmetrically about the midpoint of the long lines, which are now divided into sixths or eighths, etc., instead of quarters. With the continued development of microelectronic hybrid integrated circuits the repeaters may become smaller and cheaper and have tighter tolerances. Thus, it may well be that, by the time the Cyclops system is built, a closer repeater spacing and smaller cable would be a more economical solution. Referring once more to Figure 10-3 we see that at the control center each IF line ends in a final repeater having up to 30 dB gain. The entire IF signal then passes through a variable delay unit having a delay range of a few nanoseconds. This can be done with digitally switched lengths of strip line. Following the delay unit, the 250-MHz pilot is extracted and its phase is compared with a locally synthesized 250-MHz signal. Changes in phase of the pilot are taken to signify change in the IF delay and are servoed out with the variable delay unit. In this way, we make double use of the standard frequency distribution system; not only does it supply the reference phase for the local oscillators at each antenna, but it also stabilizes the delays of the entire IF transmission system. For this compensation method to be operable, all the 250-MHz pilots and the 250-MHz references at the control center must be generated without phase ambiguity. A precise method of doing this is to divide the I-GHz standard reference frequency by 4, and to permit the divider to lock only if the 250 MHz so obtained agrees in phase (to within say -+5°) with the tenth harmonic of the 25-MHz standard reference frequency. In this way the 113
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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
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Chapter11 in analyzingthe dataproce
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Therangelimitisthenfoundbyequating_
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TABLE 5-3 PARAMETER Wavelength Tran
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angeanddirectlyasthesquareof antenn
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"_ i i i i i p = STELLAR DENSITY AT
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I-- g u. O >- I--- .d tit (]O 0 0.
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andwidth that will still give near
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acquisitionphasefor otherraces.Supp
Page 74 and 75: 1. They would transmit continuously
Page 76 and 77: and ¢-Ceti. No signals were detect
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 and 108: o 50 ----- - _ T i 20 _,o 5 ,,,5 09
Page 109 and 110: TABLk ?- I A COMPARISON OF VARIOUS
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: addedto theother IF channel. The tw
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
Page 159 and 160: 3's = unitcostof signal planelectro
Page 161 and 162: where0ma x is the maximum value of
Page 163 and 164: Roughestimates of the costs of buil
Page 165 and 166: 12. CYCLOPS AS A BEACON Although th
Page 167 and 168: 13. SEARCH STRATEGY The high direct
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Page 171 and 172: wouldfollowtheuppermost linein Figu
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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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