=  NOW 40 WPM  =  
DSP AUDIO FILTER REVIEWED BY STEVE FORD, WB8IMY IN THE AGE OF
SOFTWARE DEFINED TRANSCEIVERS, YOU MAY THINK NO ONE NEEDS AN
EXTERNAL AUDIO FILTER.  IF YOUVE HAD THE PLEASURE OF OPERATING A
RECENT DESKTOP TRANSCEIVER WITH DIGITAL SIGNAL PROCESSING DSP
FEATURES OR A SOFTWARE DEFINED RADIO SDR TRANSCEIVER, YOU KNOW THEIR
SIGNAL FILTERING ABILITIES ARE EXCELLENT.  BUT THERE ARE STILL A LOT
OF OLDER ANALOG TRANSCEIVERS IN USE, NOT TO MENTION ALL THOSE LOW
POWER QRP KIT TRANSCEIVERS THE QCX MINI IS A SANDWICH OF TWO PRINTED
CIRCUIT BOARDS.  THE MAIN BOARD, SHOWN IN FIGURE 1, COMES WITH MANY
SMD SURFACE MOUNTED DEVICE COMPONENTS ALREADY INSTALLED.  THE
BUILDER ONLY HAS TO ADD STANDARD THROUGH HOLE PARTS.  THE PARTS YOU
MUST INSERT YOURSELF HAVE ALMOST ONE PAGE DEVOTED TO EACH COMPONENT.
OCCASIONALLY, THE INSTRUCTIONS FOR INSERTING A COMPONENT RUN OVER TO
A SECOND PAGE, SO ITS A GOOD IDEA TO CHECK THE NEXT PAGE FOR
ADDITIONAL INFORMATION.  THE BOARD IS TIGHTLY PACKED, SO TAKE YOUR
TIME BUILDING IT.  LARGE, CLEAR, COLOR PHOTOS AND DRAWINGS MAKE THE
CONSTRUCTION TASK EASIER.  THE TEXT NOTES THAT ADDITIONAL HEAT FROM
YOUR SOLDERING IRON MAY BE NEEDED OCCASIONALLY BECAUSE CONNECTIONS
ARE MADE TO THE HIDDEN GROUND PLANE.  WHEN IT APPEARED MORE HEAT WAS
NEEDED, I LEFT THE SOLDERING IRON ON THE JOINT A BIT LONGER.  FIVE
TOROIDS HAVE TO BE WOUND.  T1, THE INPUT TRANSFORMER, IS CRITICAL
AND A BIT CHALLENGING THE MANUAL CALLS IT THE ONLY REALLY TRICKY
PIECE OF ASSEMBLY.  THE INPUT SIGNAL IS ROUTED TO FIVE TURNS ON T1,
WOUND ON A T50 2 TOROID ABOUT THE SIZE OF A DIME.  A MULTI TURN
WINDING ON THE SAME CORE IS RESONANT WITH A VARIABLE CAPACITOR FOR
THE BAND SELECTED.  TWO OTHER FIVE TURN WINDINGS HAVE TO BE PHASED
CORRECTLY AND AS IDENTICAL AS POSSIBLE.  DURING ALIGNMENT, THREE
VARIABLE RESISTORS COMPENSATE FOR SLIGHT DIFFERENCES BETWEEN THESE
WINDINGS.  THE MANUAL INCLUDES DETAILED INSTRUCTIONS AND SEVERAL
ILLUSTRATIONS TO HELP YOU BUILD T1.  THE MANUAL RECOMMENDS BURNING
THE INSULATION OFF THE ENAMELED WIRE USED TO WIND THE TOROIDS.  I
FOLLOWED THIS PROCEDURE, BUT DURING TESTING, THE ARRL LAB DISCOVERED
THAT IN SOME CASES, ENOUGH INSULATION WAS LEFT TO MAKE POOR SOLDERED
CONNECTIONS.  ITS PROBABLY BEST TO SCRAPE OFF THE INSULATION FIRST.
WHEN THE ASSEMBLY OF EACH BOARD IS COMPLETED, THE TWO BOARDS PLUG
TOGETHER AS A SANDWICH WITH THE DISPLAY BOARD ON TOP SEE FIGURE 2.
I HAD A MINOR ISSUE ASSEMBLING THE UNIT IN ITS OPTIONAL ENCLOSURE,
BUT AFTER RE READING THE INSTRUCTIONS, I REALIZED THAT THE CASE
WOULD GO ON ONLY ONE WAY.  THE COMPLETE ALIGNMENT PROCEDURE IS BRIEF
AND CAN BE ACCOMPLISHED QUICKLY.  IF FOR SOME REASON YOU ARE NOT
HAPPY WITH THE RESULT, YOU CAN RUN THROUGH THE ALIGNMENT PROCEDURE
AGAIN.  THE QCX MINI HAS BUILT IN TROUBLESHOOTING CAPABILITY, AND
THE MANUAL INCLUDES APPROXIMATELY 40 PAGES OF CIRCUIT AND
TROUBLESHOOTING INFORMATION.  AS WITH MOST QRP TRANSCEIVERS AND
KITS, THERES AN ACTIVE ONLINE GROUP WITH OTHER BUILDERS WILLING TO
HELP SEE GROUPS.IO /G/ QRPLABS.  A NICE ADDED BENEFIT
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