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

y equatorially mounting the antenna elements; it is the
array that is alt-azimuth.) _If the field is being photographed
we may wish to rotate the camera at the
appropriate rate. If the image is being stored in a signal
averager we may wish to "rotate" the addresses. We have
not had time to study this problem in detail.
UNDESIRED
Terrestrial
SIGNALS
Transmitters
Most radio astronomy today uses several frequency
bands that have been set aside specifically for that purpose
by governmental agencies. No terrestrial transmitters are
permitted within these bands, which eliminates most
interference to radio astronomy. Nevertheless, radio
astronomers encounter interference from a variety of
transmitters. Radars often radiate small but troublesome
signals far outside their nominal pass bands. Harmonics
or unexpected mixing products appear in radioastronomy
bands from stations operating nominally
legally. Thus, even though radio astronomy is done
largely in "protected" bands, interference from terrestrial
transmitters is a problem.
Cyclops, on the other hand, will not always operate
in protected bands, but over a wide frequency range
occupied by thousands of terrestrial transmitters. Calculations
have been made which indicate that UHF TV
stations will not only be detectable, but will overload
any reasonable receiver. Lower powered stations will be
detectable for several hundred miles. Any flying object
will be detectable out to lunar distances.
A certain degree of interference reduction can be
achieved by generating a secondary beam that is larger
than, and concentric with, the main beam. Subtraction
of these two signals then removes most of the interferences.
It will probably be necessary to catalog all known
transmitters and program the central computer to ignore
them. Unfortunately, this creates many "blind" frequencies
for Cyclops, and still does not include flying or
time-varying transmitters. Alternatively, a quiet zone
could be created for some reasonable distance surrounding
the Cyclops
array.
REFERENCES
1. Golay, M.J.E.: Note on Coherence vs. Narrow-
Bandedness in Regeneration Oscillators, Masers,
Lasers, etc. Proc. IRE, vol. 49, no. 5, May 1961,
pp. 958-959.
2. Golay, M.J.E.: Note on the Probable Character of
Intelligent Radio Signals From Other Planetary
Systems. Proc. IRE, vol. 49, no. 5, 1961, p. 959.
3. Bracewell, R.N.: Defining the Coherence of a Signal.
Proc. IRE, vol. 50, no. 2, 1962, p. 214.
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Proc. IRE, vol. 50, no. 2, 1962, p. 214.
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Proc. IRE, vol. 53, no. 7, pp. 696-704.
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the Machine Calculation of Complex Fourier
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7. Goodman, J.W.: Introduction to Fourier Optics.
McGraw Hill, 1968.
8. Thomas, C.E.: Optical Spectrum Analysis of Large
Space Bandwidth Signals. Applied Optics, vol. 5,
1966, p. 1782.
9. Markevitch, R.V.: Optical Processing of Wideband
Signals. Third Annual Wideband Recording
Symposium, Rome Air Development Center, Apr.
1969.
10. Mamikumian, G.; and Briggs, M.H., eds.: Current
Aspects of Exobiology. Ch. 9, 1965.
11. Oliver, B.M.: Acoustic Image Synthesis, unpublished
memorandum.
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Australian J. Phys., vol. 14, no. 4, 1961, pp.
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