=  NOW 40 WPM  =  

FOR A SPECIFIC POINT ON THE GROUND.  THIS IS A VERY POWERFUL FEATURE
OF THE SOFTWARE, BUT IT REQUIRES YOU TO GENERATE A FILE SHOWING THE
PROFILE OF THE GROUND IN FRONT OF YOUR ANTENNA.  FOR OUR RUNS, THE
FLAT.PRO FILE WAS USED, WHICH MEANS THE GROUND IN FRONT OF THE
ANTENNA WAS PERFECTLY FLAT . THE FREQUENCY IS SPECIFIED AS 14R1
MEGAHERTZ.  IN THE FOUR DIFFERENT CONFIGURATIONS TO BE CALCULATED,
ALL OF THE YAGIS ARE SPECIFIED AS HAVING THREE ELEMENTS.
Combination number 1 ha AND FOR THREE ANTENNAS, THE IMPEDANCE IS
ABOUT 17 W.  THE PS 3B PHASING RELAY UNIT HAS A BROAD BANDWIDTH,
HIGH POWER, IMPEDANCE MATCHING TRANSFORMER THAT TAKES THE LOWER
RESISTANCES OF 25 OR 17 W AND MATCHES THEM TO 50 W.  TO MAINTAIN
PROPER PHASING, THE FEED LINES TO EACH ANTENNA SHOULD BE THE SAME
LENGTHS. THE LARGEST ADVANTAGE OF STACKING ANTENNAS IS NOT
NECESSARILY THE ADDITIONAL GAIN, BUT THE ABILITY TO MOVE ANTENNA
NULLS SO A DESIRED SIGNAL DOESNT FALL INTO ONE.  WHILE GAIN MAKES A
MARGINAL IMPROVEMENT, MOVING A NULL CAN MAKE THE DIFFERENCE BETWEEN
A BARELY READABLE SIGNAL AND ONE THAT IS STRONG ENOUGH TO MAKE A
RARE DX CONTACT. YOU WILL ALWAYS WANT THE DESIRED SIGNAL TO BE IN
THE MAIN LOBE OF THE ANTENNA RATHER THAN A SIDE LOBE, AND DEFINITELY
NOT IN A DEEP NULL.  A YAGI AT THE TOP OF A 60 FOOT TOWER HAS A MAIN
LOBE THAT IS NOT ALWAYS OPTIMAL FOR THE DESIRED PATH.  THIS IS
BECAUSE THE TOA FOR THE DESIRED SIGNAL IS NOT THE SAME AS THE
ANTENNAS MAIN LOBE.  A SINGLE ANTENNA INSTALLED AT MORE THAN 1
WAVELENGTH ABOVE GROUND HAS SEVERAL LOW ANGLE LOBES, WITH DEEP NULLS
BETWEEN EACH LOBE. THESE NULLS CAN BE MINUS 20 DB OR GREATER.  FROM
MY LOCATION IN GEORGIA, AUSTRALIA IS ABOUT 10,000 MILES AWAY, ITALY
IS ABOUT 5,000 MILES AWAY, AND SAINT LUCIA IS ABOUT 2,000 MILES
AWAY.  THE OPTIMAL TOA IS QUITE DIFFERENT FOR EACH OF THESE
LOCATIONS.  FOR A FARAWAY DX STATION, LOWER TOAS ARE THE MOST
USEFUL.  FOR CLOSER STATIONS, HIGHER TOAS ARE MORE USEFUL. WHEN
USING A STACKED ARRAY, YOU CAN MAINTAIN COMMUNICATION OVER THE
DESIRED PATH BECAUSE YOU CAN INSTANTANEOUSLY CHANGE THE TOA.  YOU
CAN SELECT COMBINATIONS OF STACKED ANTENNAS, OR A SINGLE ANTENNA, TO
PUT THE DX STATION IN THE MAIN LOBE OF THE ANTENNA INSTEAD OF A DEEP
NULL. ALTERNATIVELY, YOU CAN DROP A STRONG, INTERFERING STATION INTO
THE NULL OF THE ANTENNA PATTERN SO THAT YOU CAN COPY THE DESIRED
SIGNAL.  YOU CAN ALSO MOVE THE MAIN LOBE AND NULLS BY FEEDING SOME
OF THE ANTENNAS OUT OF PHASE. WITH ITS DIFFERENT TOAS, A STACKED
ARRAY IS HELPFUL FOR MAINTAINING CONTACT DURING CHANGING AND
MARGINAL BAND CONDITIONS.  DURING A DX BAND OPENING, THE INITIAL
SIGNALS USUALLY APPEAR AT LOW ELEVATION ANGLES.  AS THE BAND
STRENGTHENS AND SPREADS, SIGNALS AT HIGHER ELEVATION ANGLES ARE THE
STRONGEST.  AS THE BAND CLOSES, SIGNALS AT LOW ANGLES WILL AGAIN BE
THE STRONGEST.  BECAUSE A STACKED ARRAY ALLOWS FOR DIFFERENT TOAS
AND ADDITIONAL GAIN, IT STRETCHES THE BAND OPENING.  YOU CAN
SOMETIMES CONTACT DX STATIONS BEFORE OTHER LOCAL STATIONS CAN HEAR
THEM, IN ADDITION TO WORKING THEM LONG AFTER OTHER LOCAL STATIONS
LOSE PROPAGATION.
=  END OF 40 WPM TEXT  =  QST DE W1AW  <