‰  NOW 40 WPM  ‰  
0R80 / 3R58, OR 220 FEET.  THUS, THE EXTENSION NEEDED IS 66 FEET.
IN THE ADMITTANCE WORLD, MEASUREMENTS ARE NORMALIZED TO A VALUE OF
0R02, THE RECIPROCAL OF 50 TO WHICH IMPEDANCE IS NORMALIZED.  SO,
THE NORMALIZED 1R35 VALUE NEEDED FOR A SHUNT MATCH INDICATES A TRUE
SUSCEPTANCE OF 0R027 MHOS.  TO CONVERT THIS VALUE TO A REACTANCE, WE
TAKE ITS RECIPROCAL, AND GET 37.  THIS IS THE VALUE OF CAPACITIVE
REACTANCE THAT NEEDS TO BE PLACED IN PARALLEL WITH THE END OF THE
EXTENDED CO 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 RESISTIVE AXIS OF THE SMITH CHART SEE FIGURE 1 IS
THE ONLY STRAIGHT LINE ON THE CHART.  ITS NORMALIZED MIDDLE VALUE IS
1.  TO THE LEFT SIDE, THE VALUES APPROACH 0 TO THE RIGHT SIDE, THE
VALUES APPROACH INFINITY.  THE REACTIVE AXIS OF THE SMITH CHART IS
THE OUTER PERIMETER.  THE NORMALIZED VALUE AT THE TOP CENTER IS 1 OF
INDUCTIVE REACTANCE, AND THE VALUE AT THE BOTTOM CENTER IS 1 OF
CAPACITIVE REACTANCE.  AS WITH THE RESISTIVE AXIS, VALUES TO ONE
SIDE OF THE CHART APPROACH ZERO, AND VALUES TO THE OTHER SIDE
APPROACH INFINITY.  THE 50 COAX FROM MY VERY SHORT, 80 METER COIL
LOADED ROTATABLE DIPOLE PRESENTED AN IMPEDANCE OF 135 J 90 TO MY RIG
AT 3580 KHZ THE J INDICATES A CAPACITIVE REACTANCE.  135 J90
NORMALIZES TO 2R7 J1R8 AND IS PLOTTED AT POINT Z IN FIGURE 1.  POINT
Z ESTABLISHES THE RADIUS OF SWR CIRCLE C1, WHICH IS CONCENTRIC WITH
THE CENTER OF THE CHART.  THE SWR CIRCLE TRAVERSES ALL THE
IMPEDANCES ALONG A HALF WAVELENGTH OF THE COAX THE IMPEDANCES REPEAT
EVERY HALF WAVE.  THE RIGHT MOST VALUE WHERE CIRCLE C1 CROSSES THE
STRAIGHT, RESISTIVE AXIS INDICATES THE SWR ON THE COAX 4 1 IN THIS
CASE.  WE WANT TO GET FROM CIRCLE C1 TO THE CENTER OF THE CHART,
WHICH
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ