Relative Performance Capability of Microwave &

Optical SETI Systems

Radobs 10

The following graph summarizes the relative performance capabilities of
symmetrical Microwave and Optical SETI systems for equal transmitter powers
over ranges up to a few thousand light years.  The measure of performance is
the relative Signal-To-Noise Ratio (SNR) produced for the same transmitter
power and detection bandwidth.  The only sources of noise considered are kT
thermal noise or hf quantum noise, whichever is applicable.

Performance and guesstimated costs shown are for ground-based receivers
only.  Optical receivers are assumed to employ adaptive optics.


                         PERFORMANCE COMPARISON CHART

Relative SNR
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  0.0 dB |____System 5: Project Cyclops___________Cost = $10 Billion__
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-22.5 dB |____System 3: Visible___________________Cost = $100 Million_
         |
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-34.5 dB |____System 2: Infrared__________________Cost = $100 Million_
-36.5 dB |____System 1: Microwave_________________Cost = $100 Million_
         |
-41.0 dB |____System 4: Visible___________________Cost = $100 Million_
         |
         |
          ------------------------------------------------------------












TRANSMITTER SYSTEM DESCRIPTIONS

System 1: Microwave - Arecibo Size
          300 meter diameter dish at 1.5 GHz.
          Circular beamwidth 0.04 deg X 0.04 deg.
          Beam dimensions at 10 L.Y. = 514 A.U. X 514 A.U..

System 2: Infrared
          10 meter diameter telescope at 10,600 nm.
          Circular beamwidth 0.22" X 0.22".
          Beam dimensions at 10 L.Y. = 0.77 A.U. X 0.77 A.U..

System 3: Visible
          10 meter diameter telescope at 656 nm.
          Circular beamwidth 0.014" X 0.014".
          Beam dimensions at 10 L.Y. = 0.051 A.U. X 0.051 A.U..

System 4: Visible
          10 meter diameter telescope at 656 nm.
          Fan-shaped beamwidth 1" X 0.014".
          Beam dimensions at 10 L.Y. = 3.8 A.U. X 0.051 A.U..

System 5: Microwave - Cyclops
          6.4 km diameter farm consisting of 900 dishes, each 100 meters in
          diameter and operating at 1.5 GHz.
          Circular beamwidth 6.5" X 6.5".
          Beam dimensions at 10 L.Y. = 24 A.U. X 24 A.U..


The approximate 100:1 increase in cost for System 5 over System 3 is a lot
to pay for just an extra 22.5 dB in SNR.  If you still don't believe that
ATCs can hit "the bull's eye", consider System 4 which has a fan-shaped
transmitter beam.  This considerably relaxes the targeting problem along the
target star system's plane of ecliptic, if the latter is approximately along
the line-of-sight.


December 23, 1990
RADOBS.10
BBOARD No. 278


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Dr. Stuart A. Kingsley                       Copyright (c), 1990        *
* AMIEE, SMIEEE                                                           *
* Consultant                            "Where No Photon Has Gone Before" *
*                                                   __________            *
* FIBERDYNE OPTOELECTRONICS                        /          \           *
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