‰  NOW 40 WPM  ‰  TEXT IS FROM DECEMBER 2008 QST  PAGES 33, 35 AND 74  ‰

OPTIONAL MANUAL LEVEL CONTROL, R9, IS A GOOD IDEA IF YOU DO MUCH BINAURAL
LISTENING.  FOR MORE IN DEPTH INFORMATION ON THE QSD AND I Q SIGNALS IN
GENERAL, A SERIES OF ARTICLES THAT APPEARED IN QEX MAGAZINE IS WELL WORTH
READING.  THE LOCAL OSCILLATOR THE LO CA
‰  FROM PAGE 74  ‰
466 2 12 2,228 MDC Burlington Co RC K2TD 458 2 19 2,206 SNJ West River RC

AND Q COMPONENTS AS A FUNCTION OF TIME, YOU KNOW, LITERALLY, EVERYTHING
THERE IS TO KNOW ABOUT THAT SIGNAL.  IF THE I AND Q SIGNALS ARE DIGITIZED,
BY FEEDING THEM INTO A COMPUTER SOUND CARD, FOR INSTANCE, THE WIDE WORLD OF
DIGITAL SIGNAL PROCESSING OPENS UP.  WITH THE APPROPRIATE SOFTWARE, ALL
MODULATION MODES AM, FM, CW, SSB, PSK AND ANY OTHERS CAN BE DETECTED.  THE
OTHER MODULE SHOWN IN FIGURE 7 IS THE LOCAL OSCILLATOR LO THAT FEEDS THE I
Q DETECTOR.  ITS SIMPLY A TUNABLE FREQUENCY GENERATOR RUNNING AT A
FREQUENCY FOUR TIMES THE RECEIVED FREQUENCY PLUS 4000 KHZ.  NOW FOR A FEW
DETAILS THE I Q DETECTOR THE HEART OF THE RECEIVER IS SHOWN IN FIGURE 8.
ITS A VERY CLEVER AND ELEGANT CIRCUIT KNOWN AS A QUAD SAMPLING DETECTOR QSD
THAT SEPARATES THE IN PHASE AND QUADRATURE PHASE COMPONENTS OF THE INCOMING
SIGNAL.  ITS ALSO REFERRED TO AS A TAYLOE DETECTOR.  BASICALLY, IT CONSISTS
OF AN ARRAY OF FOUR FAST ANALOG SWITCHES U1 THAT ENDLESSLY AND SEQUENTIALLY
SAMPLE THE INCOMING SIGNAL AT A RATE FOUR TIMES THE DESIRED IF FREQUENCY.
‰  FROM PAGE 74  ‰
Organization KD8BNV KE8PX 381 2 34 2,336 OH San Joaquin Valley ARS WA6SJV
WA6WTF 509 2 30 2,336 SJV Chicago Suburban Radio Assn N9BAT 499 2 36 2,304

A MODULAR RECEIVER FOR EXPLORING THE LF/VLF BANDS PART 1, LAST MONTH,
PRESENTED THE FRONT END PIECES OF A HIGH PERFORMANCE LF/VLF RECEIVER.  THEY
ALSO COULD BE USED TO MAKE A STAND ALONE CONVERTER TO USE WITH YOUR 80
METER AMATEUR RECEIVER OR TRANSCEIVER.  LAST MONTHS ARTICLE ALSO PROVIDED A
SIDEBAR WHATS DOWN THERE?  TO PROVIDE A BRIEF OVERVIEW OF THE INTERESTING
LISTENING TO BE FOUND IN THAT REGION OF THE SPECTRUM.  THIS MONTH WE WILL
COMPLETE THE PROJECT BY MAKING OUR OWN LF/ VLF SOFTWARE DEFINED RADIO SDR
RECEIVER.  A BRIEF LOOK AT THE DESIGN THE THREE MODULES MAKING UP THE
RECEIVER ARE SHOWN IN FIGURE 6 AND IN BLOCK DIAGRAM FORM IN FIGURE 7.
DETAILS OF THE CONVERTER AND ANTENNA POSSIBILITIES APPEAR IN PART 1.
FOLLOWING THE CONVERTER IN FIGURE 7 IS THE I Q DETECTOR.  THIS IS THE REAL
HEART OF THE RECEIVER AND ITS NAME STEMS FROM THE FACT THAT ITS FUNCTION IS
TO EXTRACT BOTH AN IN PHASE I COMPONENT OF THE SIGNAL AS WELL AS A 90 OUT
OF PHASE Q, OR QUADRATURE, COMPONENT.  THIS IS THE APPROACH FOLLOWED IN
MOST MODERN RADIO DESIGNS.  THE REASON I Q DETECTION IS SUCH A FAVORED
TECHNIQUE AMONG RECEIVER DESIGN ENGINEERS IS THAT ONCE YOU HAVE BOTH THE I
‰  FROM PAGE 74  ‰
ID W0EA 621 2 3 2,416 IA The FPL Group K8ESQ K8QBR 533 2 5 2,406 MI Barrie
ARC VE3GCB VE3ORC 475 2 36 2,380 ON Hamilton ARC VE3DC VE3DF 940 2 40 2,380
ON CTARC WD5IYF KE5OMZ 628 2 12 2,372 OK Wyandot Area Ham Operators
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ