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ARTICLE.  AUDIO SECTION THE TOP HALF OF THE PC BOARD CONTAINS ALL OF THE
AUDIO CIRCUITRY.  THERE ARE NO PC BOARD TRACES CONNECTING THE TWO HALVES,
AND IT IS OKAY TO CUT THE BOARD INTO SEPARATE FUNCTIONAL BLOCKS FOR
PACKAGING FLEXIBILITY, OR TO USE THE AUDIO AND RF PORTIONS OF THE CIRCUITRY
IN OTHER PROJECTS.  SPEECH AMPLIFIER THE SPEECH AMPLIFIER DRIVES A PASSIVE
LOW PASS FILTER USING TWO SERIES INDUCTORS AND THREE SHUNT CAPACITORS.  THE
COMBINATION OF THIS LOW PASS FILTER AND THE MIXER IF PORT FILTERS LIMITS
SPEECH FREQUENCIES TO JUST OVER 3 KHZ FOR NATURAL SOUNDING SPEECH AND GOOD
SPECTRAL PURITY.  THERE IS NO RIPPLE IN THE AUDIO PASSBAND.  ANALOG SIGNAL
PROCESSOR THE ANALOG SIGNAL PROCESSOR AND BASEBAND AMPLITUDE AND PHASE TRIM
CIRCUITRY ARE TAKEN DIRECTLY FROM FIGURES 9R56 AND 9R35 OF EMRFD.  THE
POSITION OF THE SIDEBAND SELECT SWITCH IN THE SIGNAL PATH ALLOWS SWITCHING
WITHOUT READJUSTING THE AMPLITUDE AND PHASE TRIMMERS.  FOR MOST
APPLICATIONS, ONE SIDEBAND WILL BE USED EXCLUSIVELY, AND THE SIDEBAND
‰  FROM PAGE 92  ‰
Hickory Lake Contest Club K2NNY 737 1 4 1,165 NNY KD8SQ 509 2 2 1,018 OH
Findlay RC W8FT 155 2 20 616 OH CT RI Contest Group W1R 239 2 2 562 CT W7JQ
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