‰  NOW 35 WPM  ‰  TEXT IS FROM MAY 2015  QST  PAGE 61 ‰

THE DOCTOR IS IN SOMETIMES YOU GET SIDEBAND REVERSAL SOMETIMES YOU DONT Q
THERE IS A CONTINUING DISCUSSION ON SOME MAIL LIST FORUMS ARGUING THAT YOU
DONT GET SIDEBAND REVERSAL ON 75 METERS WITH A 9 MHZ SSB IF AND 5 MHZ VFO.
IT WAS MY DISTINCT EXPERIENCE THAT IT HAPPENED WITH THE GEAR I BUILT IN THE
EARLY 60S.  A SIDEBAND REVERSAL OCCURS IN MIXING ONLY IF THE SIGNAL WITH
THE MODULATION IS SUBTRACTED FROM THE SIGNAL THAT ISNT MODULATED, TYPICALLY
THE VFO.  SO IN THE CASE OF A 9 MHZ SSB SIGNAL MIXED WITH A 5 MHZ VFO, WE
GET.  LETS SUPPOSE THAT THE 9 MHZ IS AN SSB SIGNAL OF UPPER SIDEBAND USB
VARIETY AND THE MODULATION IS 1 KHZ.  WITH USB, THE SIGNAL HAS THE
MODULATING SIGNAL ABOVE THE SUPPRESSED CARRIER FREQUENCY AND BELOW FOR
LOWER SIDEBAND LSB.  THEN A 9R001 AND A B 14R001, AND A B 4R001 MHZ, BOTH
PRODUCTS STILL USB, AS WAS THE 9 MHZ IF SIGNAL.  BUT IF WE TRY IT THE OTHER
WAY WITH A 5 MHZ SSB SIGNAL AND A 9 MHZ VFO, THE STORY IS DIFFERENT SEE
FIGURE 1.  IN THIS CASE, A B 9 5 14, AND A B 9 5 4 MHZ, SO FAR THEY SEEM
SIMILAR TO THE EARLIER CASE.  IF WE PUT USB MODULATION OF A 1 KHZ TONE ON
THE 5 MHZ SIGNAL WE HAVE 5R001 MHZ.  NOW A B 9 5R001 14R001 USB, BUT A B 9
5R001 3R999 MHZ LSB, SO WE DO HAVE SIDEBAND REVERSAL IN THIS CASE, BECAUSE
WE ARE SUBTRACTING THE SIGNAL WITH THE MODULATION.  THIS HAS BEEN A SOURCE
OF CONFUSION FOR A LONG TIME, AND I EVEN HAD IT WRONG IN A COLUMN YEARS AGO
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ