‰  NOW 35 WPM  ‰  TEXT IS FROM FEBRUARY 2020  QST  PAGE 43 ‰

AN SWR SHIFTING T  BILL CONWELL, K2PO  ANY FEED LINE MISMATCH CAN BE
BROUGHT TO A 1 1 SWR WITH A SINGLE SHUNT CAPACITOR, PROVIDED ITS VALUE AND
THE LOCATION WHERE IT BRIDGES THE COAXIAL CENTER AND SHIELD CONDUCTORS IS
CHOSEN CORRECTLY.  THIS IS BECAUSE THERE ARE TWO LOCATIONS AT EVERY HALF
WAVE ALONG A MISMATCHED FEED LINE WHERE THE IMPEDANCE IS EXACTLY 50 IN
PARALLEL WITH A REACTIVE COMPONENT.  BY EXTENDING OR SHORTENING THE COAX SO
THAT ONE OF THESE LOCATIONS IS AT THE TRANSMITTER END OF THE COAX, A
COUNTER REACTIVE SHUNT COMPONENT CAN BE APPLIED USING A COAXIAL T CONNECTOR
SEE THE LEAD PHOTO, THUS BRINGING THE SWR TO 1 1.  THE SHUNT COMPONENT CAN
BE UNSCREWED WHEN DESIRED TO RESTORE THE ANTENNA TO ITS ORIGINAL TUNING.
USING THE SMITH CHART  THE SMITH CHART, INVENTED BY PHILLIP SMITH, IS A
TOOL THAT ENABLES US TO DETERMINE THE VALUE OF THE NECESSARY REACTIVE
COMPONENT AND ITS TRANSMISSION LINE LOCATION TO ACHIEVE A MATCH IN MY CASE,
TRANSFORMING A 4 1 SWR IN THE 80 METER RTTY BAND TO 1 1.  TO DETERMINE COAX
EXTENSION AND SHUNT REACTANCE WITH THE SMITH CHART, WE START BY USING AN
ANTENNA ANALYZER TO MEASURE THE IMPEDANCE THE FEED LINE PRESENTS TO THE RIG
AT THE FREQUENCY OF INTEREST, AND THEN NORMALIZING IT TO PLOT ON THE SMITH
CHART.  NORMALIZING SIMPLY INVOLVES DIVIDING THE RESISTIVE AND REACTIVE
PARTS OF THE MEASURED IMPEDANCE BY THE TRANSMISSION LINE IMPEDANCE.  THE
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ