Message #204409

[Jennifer Murdoch]

Domestic Radio Signals

       Sullivan et al (1978) and Sullivan (1981) considered the possibility
       of eavesdropping on  radio emissions  inadvertently  "leaking"  from
       other technical civilizations.  To better understand the information
       which might be derived from radio leakage, the case  of  our  planet
       Earth was analyzed.   As  an  example,  they  showed that the United
       States Naval Space  Surveillance   System   (Breetz,  1968)  has  an
       effective radiated power of 1.4x10exp (10) watts into a bandwidth of
       only 0.1 Hz.   Its  beam  is  such  that  any  eavesdropper  in  the
       declination range of zero to 33 degrees (28 percent of the sky) will
       be illuminated daily  for  a  period of roughly seven seconds.  This
       radar has a detectability range of  leaking  terrestrial  signals to
       sixty light years  for an Arecibo-type (305-meter)  antenna  at  the
       receiving end, or  six  hundred light years for a Cyclops array (one
       thousand dishes of 100-meter size each).

       Recently Billingham and Tarter (1992) estimated the maximum range at
       which radar signals from Earth could be detected by a search similar
       to the NASA High Resolution Microwave  Survey  (HRMS)  assumed to be
       operating somewhere in  the  Milky  Way galaxy.  They  examined  the
       transmission of the  planetary  radar  of  Arecibo and the ballistic
       missile early warning  systems  (BMEWS).   For  the  calculation  of
       maximum range R, the standard range equation is:

               R=(EIRP/(4PI PHImin))exp(1/2)


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