‰  NOW 30 WPM  ‰  TEXT IS FROM JANUARY 2016 QST  PAGE 45‰

SPHERE AREA OCCUPIED BY THE PATCH TIMES THE TOTAL POWER TRANSMITTED.
LOOKING BACK TO HIGH SCHOOL GEOMETRY, WE RECALL OR COULD LOOK UP THAT THE
AREA OF A SPHERE IS.  THUS THE ACTUAL RECEIVED ENERGY IS JUST R THE RADIUS
OF THE SPHERE, OR EQUIVALENTLY, THE DISTANCE BETWEEN THE TRANSMIT AND
RECEIVE ANTENNAS.  THE USUAL UNITS ARE WATTS W FOR TRANSMIT AND RECEIVE
POWER, METERS M FOR DISTANCE AND SQUARE METERS FOR RECEIVE ANTENNA AREA.
ONE IMPORTANT RESULT THAT WE CAN TAKE FROM THIS IS THAT THE RECEIVE POWER
IS REDUCED IN PROPORTION TO THE SQUARE OF THE DISTANCE, AN IMPORTANT
CONCEPT OFTEN REFERRED TO AS THE INVERSE SQUARE LAW.  WHATS THE RECEIVE
ANTENNA AREA?  THIS IDEA MAKES A GREAT PICTURE, BUT BEFORE WE CAN MAKE MUCH
USE OF IT, WE NEED TO KNOW HOW TO DETERMINE THE EFFECTIVE AREA OF A RECEIVE
ANTENNA.  PERHAPS THE EASIEST TO UNDERSTAND IS A PARABOLIC DISH ANTENNA,
OFTEN USED FOR SATELLITE RECEPTION, AS WELL AS POINT TO POINT MICROWAVE
LINKS AND RADAR SYSTEMS SEE FIGURE 2.  IN THIS CASE THE AREA, PERHAPS NOT
SURPRISINGLY, IS CLOSE TO THAT OF THE OPENING OR MOUTH OF THE DISH.  REAL
WORLD BEING WHAT IT IS, IT CAN NEVER QUITE REACH THE FULL PHYSICAL APERTURE
‰  END OF 30 WPM TEXT  ‰  QST DE W1AW  ƒ