‰  NOW 35 WPM  ‰  TEXT IS FROM SEPTEMBER 2018  QST  PAGE 53 ‰

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
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ