=  NOW 25 WPM  =  TEXT IS FROM JANUARY 2020  QST  PAGE 58 =

FREQUENCY MIGHT SEEM AS THOUGH WE HAVE EXCEEDED THE SPEED OF LIGHT, BUT IS
ACTUALLY A WAVEGUIDE PHENOMENON CALLED PHASE VELOCITY.  ONLY THE PHASE
VELOCITY EXCEEDS THE SPEED OF LIGHT ENERGY CANNOT TRAVEL FASTER.  THE GUIDE
WAVELENGTH G VARIES WITH FREQUENCY AS A FUNCTION OF THE CUTOFF FREQUENCY
WHICH IS MUCH LONGER THAN THE FREE SPACE WAVELENGTH R0 NEAR THE CUTOFF
FREQUENCY AND BECOMES CLOSER TO R0 AS FREQUENCY INCREASES.  FOR THE
WAVEGUIDE IN FIGURE 2, CUTOFF WAVELENGTH IS TWICE THE WIDTH OF 2R29 INCHES
5R82 CENTIMETERS, OR 11R63 CENTIMETERS, FOR A CUTOFF FREQUENCY OF 2R58 GHZ.
THE CUTOFF FREQUENCY MAY BE MEASURED BY REDUCING THE SOURCE FREQUENCY UNTIL
NO ENERGY IS DETECTED IN THE GUIDE.  THE DETECTED SIGNAL LEVEL DROPPED
RAPIDLY AS THE SOURCE FREQUENCY DECREASED FROM 2R7 TO 2R6 GHZ.  I ALSO MADE
A SMALLER TEST WAVEGUIDE SEE FIGURE 4 APPROXIMATELY WR 187 SIZE 1R872 X
0R872 INCHES BY FOLDING ANOTHER PIECE OF COPPER MESH INTO A RECTANGULAR
=  END OF 25 WPM TEXT  =  QST DE W1AW  <