‰  NOW 40 WPM  ‰  TEXT IS FROM JULY 2014 QST  PAGE 55‰
PRODUCTS OF STRONG NEARBY SIGNALS THAT THE GUTTER CAN RADIATE TOWARD YOUR
ANTENNA.  Q I WAS HAVING BREAKFAST WITH A GROUP OF LOCAL HAMS, WHEN THE
TOPIC OF HF MOBILE OPERATION CAME UP.  I MENTIONED THAT I HAD USED A PIECE
OF BRAID TO TIE THE CHASSIS OF MY PICKUP TRUCK TO THE BED AND ALSO TO THE
BASE OF MY HF MOBILE ANTENNA.  THE GENTLEMAN ON THE OTHER SIDE OF THE TABLE
MENTIONED HE HAD TAKEN THIS IDEA ONE STEP FURTHER.  HE TOOK THE SHIELD
BRAID OFF SOME COAX, TIED IT TO THE TRUC

SIZE, OR INSULATION IS NOT AS DESIGNED.  THERE HAVE BEEN A FEW RECENT QST
ARTICLES DESCRIBING THE DESIGN OF SUCH AN ANTENNA.  USING 14 AWG BARE
COPPER WIRE, EZNEC PREDICTS THAT THE IMPEDANCE OF 122R6 FEET OF WIRE, 47
FEET HIGH AT 10R125 MHZ WILL BE SOMEWHAT DIFFERENT THAN W5JH PREDICTED IN
REFERENCE 2.  ONE THING TO KEEP IN MIND IS THAT THE WHOLE MATCHING ISSUE
CAN BE SIDESTEPPED IF YOU RUN WINDOW LINE ALL THE WAY BACK TO A WIDE RANGE
TUNER NEAR THE RADIO.  THE ANTENNA WILL RADIATE WITH THE SAME PATTERN AND
GAIN, BUT YOU WONT HAVE TO FUSS WITH THE MATCH AT THE ANTENNA FEED, AND YOU
WILL HAVE THE ADDED BENEFIT THAT THE ANTENNA WILL WORK WELL BUT WITH
DIFFERENT PATTERNS ON ALL BANDS FROM 80 TO 6 METERS.  THE EXACT LENGTH AND
RESONANCE OF THE ANTENNA IS NOT PARTICULARLY CRITICAL.  IN GENERAL, SHORTER
LENGTHS WILL HAVE SOMEWHAT REDUCED GAIN, BUT LOWER LEVEL SIDELOBES, WHILE
SOMEWHAT LONGER ANTENNAS WILL HAVE LARGER SIDELOBES.  AS EXAMPLES, REDUCING
THE LENGTH TO 110 FEET WILL RESULT IN A PEAK GAIN OF 10 DBI DOWN FROM 10R37
WITH SIDELOBES AT 21 DB, WHILE A 130 FOOT LENGTH WILL PROVIDE 9R7 DBI GAIN,
WITH THE SIDELOBES DOWN ONLY 7 DB.  DIFFERENT LENGTHS WILL REQUIRE

THE DOCTOR IS IN JOEL R. HALLAS, W1ZR, W1ZR ARRL. ORG  HOW DO YOU ADJUST A
NON RESONANT ANTENNA?   Q I JUST PUT UP AN EXTENDED DOUBLE ZEPP EDZ ANTENNA
FOR 30 METERS.  TO GET THE SWR DOWN, DO I ADJUST THE LENGTH OF THE ANTENNA,
OR DO I ADJUST THE LENGTH OF THE 450 MATCHING SECTION?  THE ONLY AVAILABLE
MEASUREMENT EQUIPMENT I HAVE IS AN SWR BRIDGE.  SHOULD I USE MY 4 1 BALUN
BETWEEN THE MATCHING SECTION AND THE COAX?  A THE EDZ SEE FIGURE 1 IS A
GREAT ANTENNA.  IT PROVIDES AS MUCH BROADSIDE GAIN AS YOU CAN GET FROM A
SINGLE ELEMENT, RESULTING IN THE SHARP PATTERN SHOWN IN BLACK IN FIGURE 2.
THIS IS GREAT IF YOU WANT TO FOCUS TOWARD THE TWO BROADSIDE DIRECTIONS.
NOTE THAT THE GAIN ACHIEVED COMPARED TO A 1/2 WAVE DIPOLE BLUE PATTERN IN
FIGURE 2 AT THE SAME HEIGHT IS ABOUT 3R1 DB, RESULTING FROM THE NARROWING
OF THE BEAMWIDTH FROM 86 TO 36 ON EACH SIDE.  AN IN BETWEEN ANTENNA IS THE
NON EXTENDED DOUBLE ZEPP, ALSO KNOWN A TWO 1/2 WAVES IN PHASE, OR FULL WAVE
DIPOLE, IS SHOWN IN RED.  THE TRICKY THING ABOUT ADJUSTING THE EDZ IS THAT,
UNLIKE THE OTHER TWO, IT ISNT NECESSARILY RESONANT IN ANY BAND, ALTHOUGH
YOUR 122R6 FOOT LENGTH SHOULD BE CLOSE TO 1/2 WAVE RESONANCE AT 3R63 MHZ
AND IT SHOULD SHOW A LOW SWR THERE, IF TEMPORARILY FED WITH 50 COAX INSTEAD
OF WINDOW LINE.  THE EXACT ANTENNA RESONANCE, AS WELL AS THE IMPEDANCE AT
10R125 MHZ WILL BE DIFFERENT FROM THE DESIGN POINT IF THE HEIGHT, WIRE
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ