‰  NOW 40 WPM  ‰  

OUTSIDE YOUR PASSBAND, GENERATED IN NON LINEAR PARTS OF YOUR
RECEIVER MIXING WITH FUNDAMENTALS OF OTHER SIGNALS NEAR, BUT OUTSIDE
OF, YOUR PASSBAND.  THE COMBINATION IS CALLED A THIRD ORDER
INTERMODULATION DISTORTION, AND CAN RESULT IN SIGNALS YOU CAN HEAR
IN YOUR PASSBAND, EVEN THOUGH THEY ARENT THERE.  THIS IS ONE
COMPONENT OF DYNAMIC RANGE THAT IS LISTED IN THE QST PRODUCT REVIEWS
OF RECEIVERS AND TRANSCEIVERS.  THE TWO TONE, THIRD ORDER DYNAMIC
RANGE AT A SPA THE DOCTOR IS IN BALUNS CAN SERVE MUTIPLE PURPOSES Q
I SEE BALUNS REFERRED TO USING NUMBERS SUCH AS 1 1, 4 1, 9 1, AND
OTHERS.  CAN YOU PLEASE EXPLAIN HOW THESE NUMBERS ARE DETERMINED,
AND HOW DO WE KNOW WHICH ONE TO USE IN A PARTICULAR APPLICATION?  A
THE PRIMARY FUNCTION OF A BALUN OR COMMON MODE CHOKE IS TO PROVIDE A
TRANSITION BETWEEN AN ELECTRICALLY BALANCED SYSTEM, SUCH AS A CENTER
FED DIPOLE ANTENNA, AND AN UNBALANCED ONE, SUCH AS A COAXIAL
TRANSMISSION LINE, OR AN UNBALANCED ANTENNA SUCH AS A GROUND PLANE.
MANY TYPES OF BALUNS ARE CONSTRUCTED OF TRANSFORMER LIKE WINDINGS.
DEPENDING ON THE DESIGN, IT IS ALSO POSSIBLE FOR THEM TO SERVE
DOUBLE DUTY AS AN IMPEDANCE TRANSFORMER.  THE NUMBERS REFER TO THE
IMPEDANCE TRANSFORMATION RATIOS.  USUALLY BUT NOT ALWAYS THE 1 SIDE
IS DESIGNED TO BE CONNECTED TO THE UNBALANCED SYSTEM, SUCH AS 50
COAX, WHILE THE OTHER SIDE IS DESIGNED TO BE CONNECTED TO THE
BALANCED LOAD.  SO, FOR EXAMPLE, A 9 1 BALUN CAN BE USED TO
INTERCONNECT 50 COAX TO A 450 BALANCED TRANSMISSION LINE.  IN SOME
CASES, A LONG TRANSMISSION LINE RUN THAT WOULD HAVE HIGH LOSSES IF
RUN OVER 50 COAX WILL BE TRANSFORMED BY A 9 1 BALUN AT EACH END,
WITH A LONG RUN OF LOWER LOSS 450 WINDOW LINE IN BETWEEN.  SEE
FIGURE 1A FOR EXAMPLES OF TRANSFORMING BALUNS USED IN MATCHED
SYSTEMS.  OFTEN, BALUNS ARE USED IN WIDE BAND, NON RESONANT, NON
MATCHED SYSTEMS.  FOR EXAMPLE, THE

POPULAR CENTER FED ZEPP ANTENNA IS JUST AN 80 OR 40 METER DIPOLE USED ON
MULTIPLE BANDS AND FED BY LOW LOSS WINDOW LINE.  THE ACTUAL IMPEDANCE AT
THE BOTTOM OF THE WINDOW LINE GOING INTO THE BALUN WILL BE DIFFERENT ON
EACH BAND, SO THE TRANSFORMER WILL NOT BE MATCHED ON ANY BAND.  WITH LUCK,
A LENGTH OF LINE, AND A TRANSFORMATION RATIO, AN ANTENNA TUNER WILL BE ABLE
TO MATCH THE SYSTEM ON ANY BAND SEE FIGURE 1B.  THE POINT IS THAT THE
BALUNS ARE NOT ALWAYS CONNECTED TO THEIR DESIGN IMPEDANCE LOADS.  Q WOULD
YOU PROVIDE A SIMPLE EXPLANATION OF HOW A HIGH STANDING WAVE RATIO SWR AT
THE ANTENNA TERMINALS CAN CAUSE DAMAGE TO THE FINAL AMPLIFIER TRANSISTORS
OR TUBES IN A TRANSCEIVER OR AMPLIFIER?  IS THE EFFECT LIKE POWER FACTOR IN
ELECTRIC MOTORS, IN WHICH THE VOLTAGE AND CURRENT ARE OUT OF PHASE, AND CAN
EXCEED COMPONENT DESIGN?  A THE ACTIONS IN THE TWO TYPES OF DEVICES IS
QUITE DIFFERENT.  WITH AN SWR GREATER THAN 1 1, THE VOLTAGE OR THE CURRENT
ON THE TRANSMISSION LINE CAN BE UP TO DOUBLE THE VOLTAGE OR CURRENT THAT
YOU WOULD HAVE WITH A MATCHED LINE AT THE SAME POWER.  MEANWHILE, THE
MATCHED LINE WILL HAVE THE SAME VOLTAGE AND CURRENT ALONG THE LENGTH OF THE
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ