‰  NOW 20 WPM  ‰  TEXT IS FROM OCTOBER 2012 QST  PAGE 44‰

ELEMENT AND TRUE TIME DELAY OPERATION JOIN TOGETHER TO PROVIDE THE
HORIZONTAL RESPONSE AS MODELED WITH 4NEC2 AND SHOWN IN FIGURE 3.  THIS
PATTERN SHAPE IS LARGELY PRESERVED OVER THE FREQUENCY RANGE, BUT THE
FORWARD GAIN DECREASES SIGNIFICANTLY AS THE OPERATING FREQUENCY IS LOWERED.
COMBINER AMPLIFIER THE COMBINER AMPLIFIER SHOWN IN FIGURE 2 IS A THREE
TERMINAL DEVICE THAT MUST PROVIDE PROPER TERMINATION FOR THE DELAY AND
REFERENCE LINES, PORT TO PORT TIMING AND AMPLITUDE ACCURACY AS WELL AS
AMPLIFICATION.  IT IS ESSENTIAL TO UNDERSTAND THE PORT CHARACTERISTICS OF
THE COMBINER AMPLIFIER BEFORE WE CONSIDER ITS INTERNAL CIRCUITRY.  THE
INPUT IMPEDANCE OF PORT A AND PORT B OF THE COMBINER AMPLIFIER MUST CLOSELY
MATCH THE CHARACTERISTIC IMPEDANCE OF THE COAX LINE IN THIS CASE 75  OVER
‰  END OF 20 WPM TEXT  ‰  QST DE W1AW  ƒ