‰  NOW 35 WPM  ‰  TEXT IS FROM AUGUST 2019 QST  PAGE 47 ‰

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
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ