‰  NOW 40 WPM  ‰  TEXT IS FROM MAY 2015  QST  PAGE 61 ‰
REQUIREMENTS OF EACH.  IN A MOBILE INSTALLATION, PARTICULARLY ONE ON THE
UPPER HF OR V/UHF BANDS, THE POWER GROUNDING HAS LITTLE OR NOTHING TO DO
WITH HOW THE ANTENNA FUNCTIONS.  IT IS IMPORTANT THAT THE COAX FEEDING THE
ANTENNA BE CONNECTED DIRECTLY TO THE ANTENNA, BOTH WITH INNER CONDUCTOR AND
SHIELD.  THIS MUST HAPPEN RIGHT AT THE ANTENNA BASE IN ORDER FOR THE
ANTENNA TO OPERATE AS DESIGNED.  EVEN AN INCH OR LESS OF EXTRA WIRE ON
EITHER SIDE CAN CHANGE THE ANTENNA TUNIN

DUE TO MISREMEMBERING WITHOUT CHECKING THE NUMBERS.  Q THERES A TV ANTENNA
MOUNTED ON MY TOWER FOR TIMES WHEN SATELLITES FADE AWAY IN RAIN OR WHEN I
WANT TO WATCH ONE OF THE 40 CHANNELS THAT ARE NOT AVAILABLE TO ME VIA MY
SATELLITE SERVICE.  IN THE 50S AND 60S THERE WERE ANTENNAS OF THIS TYPE OF
CONSTRUCTION BEING MARKETED FOR AMATEUR USE ON OUR VHF BANDS.  THERE WERE
ALSO SOME ARTICLES DESCRIBING HOW TO MODIFY STANDARD TV ANTENNAS FOR
AMATEUR USE.  IT APPEARS THAT MY VERY STANDARD MODEL IS A 300 DESIGN USING
A 1 4 BROADBAND BALUN AT THE ANTENNA TO MATCH 75 COAX CABLE.  SO, I HAVE AN
ANTENNA ON MY TOWER THAT IS ONLY USED A FEW TIMES A YEAR BUT IS POINTED
TOWARD HOUSTON, WHERE ID LIKE TO MAKE VHF CONTACTS.  IS THERE A WAY THAT I
COULD MAKE USE OF THIS ON THE 144, 222, 440, OR 900 MHZ HAM BANDS WHEN IM
NOT USING IT FOR TV?  A THE ANTENNA YOU HAVE SEE FIGURE 2 IS A CLASSIC LOG
PERIODIC, WITH A FEW TWISTS.  IT IS DESIGNED TO OPERATE ON THE LOW BAND TV
CHANNELS 2 6, 54 88 MHZ USING THE LONGER ELEMENTS IN 1/2 WAVELENGTH MODE.
THEY ARE BENT FORWARD SO THAT THEIR PATTERN WILL HAVE A MAINLY FORWARD LOBE
IN 3/2 WAVELENGTH MODE ON THE VHF HIGH BAND CHANNELS 7 13, 174 216 MHZ.

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 40 WPM TEXT  ‰  QST DE W1AW  ƒ