‰  NOW 40 WPM  ‰  
DEVELOPMENT.  THE DOWNSIDE IS THAT SOMETIMES THE DEVICE CAN BE UNSTABLE YOU
NEED TO CHOOSE THE RIGHT IMAGE WITH THE RIGHT HARDWARE.  ONE OF THE MOST
CRITICAL PARTS IS THE QUALITY OF THE MICROSD CARD.  I HAD MANY PROBLEMS IN
THE PAST WHEN USING CHEAP MICROSD CARDS WITH AN RPI BOARD.  IF I DIDNT SHUT
DOWN THE DEVICE PROPERLY, THE SOFTWARE PACKAGE GOT CORRUPTED, AND I HAD TO
RE FLASH THE CARD ALL OVER AGAIN NOT VERY GOOD IF YOU WANT TO USE IT FOR
PORTABLE OR MOBILE OPERATION.  FOR MANY 

LAB NOTES QRP LABS QCX TRANSCEIVER KIT BOB ALLISON, WB1GCM, ARRL LABORATORY
ASSISTANT MANAGER PAUL, N1II, INITIALLY BUILT AN 80 METER QCX KIT.  TESTING
IN THE ARRL LAB REVEALED A SECOND HARMONIC 37 DB BELOW THE FUNDAMENTAL.  TO
BE COMPLIANT WITH FCC PART 97 STANDARDS, 43 DB OF HARMONIC AND SPURIOUS
EMISSION IS REQUIRED.  THE 80 METER QCX ALSO GENERATED NOTICEABLE KEY
CLICKS.  WE CONTACTED HANS SUMMERS, G0UPL, AT QRP LABS.  HANS DISCOVERED
THAT THE CW RISE TIME WAS TOO FAST, GENERATING KEY CLICKS, AND CHANGED THE
VALUES OF C31, R41, AND R42 IN THE MPS751 KEYING CIRCUIT.  HE ALSO FIXED A
BUG IN THE FIRMWARE.  THESE CHANGES WERE MADE IN PRODUCTION, AND
MODIFICATION INFORMATION FOR EARLIER KITS IS AVAILABLE ON THE QRP LABS
WEBSITE.  AT PRESS TIME, HANS HAD DETERMINED THAT OUR 80 METER QCX HAD A
DEFECTIVE MPS751 IN THE KEYING CIRCUIT BUT HAD NOT FOUND OUT WHY THE
HARMONIC SUPPRESSION WAS LESS THAN EXPECTED.  WE OBTAINED A 40 METER
VERSION OF THE QCX, AND THE TEST RESULTS IN TABLE 1 ARE BASED ON THAT UNIT.
IT HAS 54 DB OF HARMONIC AND SPURIOUS EMISSION SUPPRESSION, MORE THAN
ENOUGH TO MEET FCC STANDARDS.  IT ALSO HAS ADEQUATE KEYING WAVEFORM SHAPING
TO PREVENT KEY CLICKS AND WIDE KEYING SIDEBANDS.  TRANSMITTED PHASE NOISE
IS LOW, BETTER THAN 135 DBC AT 10 AND 50 KHZ FROM THE CARRIER.  THE 40
METER QCX TRANSCEIVER IS AN OVERALL GOOD PERFORMER.  IT HAS MORE THAN

ENOUGH SENSITIVITY FOR 40 METER OPERATION AND DOES A GOOD JOB WITH STRONG
ADJACENT SIGNALS, ALTHOUGH A STRONG STATION SAY, S 9 40 DB THAT IS 2 KHZ
AWAY FROM THE TUNED FREQUENCY WILL BE HEARD WEAKLY, BLEEDING THROUGH THE
FILTER.  OF INTEREST TO FIELD OPERATORS WHO HAVE EXPERIENCED A FAILING
BATTERY, THIS LITTLE TRANSCEIVER WILL KEEP RECEIVING AND TRANSMITTING ALL
THE WAY DOWN TO A SUPPLY VOLTAGE OF 7 V DC, ALTHOUGH THE OUTPUT POWER IS
REALLY LOW AT THAT VOLTAGE.  ALTHOUGH THE QCX 40 HAS A 7 MHZ BAND PASS
FILTER, IT WILL TRANSMIT ON OTHER BANDS.  DO NOT DO THIS THE HARMONICS WILL
EXCEED FCC REQUIREMENTS.  INSTEAD, GET A QCX WITH THE APPROPRIATE FILTER
FOR THE BAND YOURE INTERESTED IN.  4 IN THE MENU SELECTS KEYER MODE, SPEED,
AND SIDETONE SETTINGS.  FROM HERE, GO TO MENU SECTION 3, VFO, TO SET THE
REST OF THE OPERATING CONDITIONS.  THIS LITTLE TRANSCEIVER ALLOWS YOU TO
SET AND VARY A HOST OF FUNCTIONS, JUST LIKE MANY FULL SIZE TABLETOP RADIOS.
IF THERE IS NO SIGN OF POWER OUTPUT, BEFORE BREAKING OUT THE TEST
EQUIPMENT, FIRST GO TO MENU ITEM 6R2 AND CHECK THAT THE MODE SELECTED IS
CW.  NEXT, GO TO MENU ITEM 4R7 AND SEE THAT THE CODE PRACTICE SETTING,
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ