‰  NOW 40 WPM  ‰  TEXT IS FROM MARCH 2009 QST  PAGES 35 AND 81  ‰

OF THE WIRE, INCLUDING THE EXTRA LENGTH, WAS UNZIPPED TO MAKE THE DIPOLE
SECTION.  AN ELECTRICIANS KNOT SEE FIGURE 1 WAS TIED AT THE JUNCTION OF THE
DIPOLE AND THE FEED LINE.  AT THE TRANSMITTER END OF THE FEED LINE I
UNZIPPED THE WIRE A COUPLE OF INCHES AND
‰  FROM PAGE 81  ‰
KA1CQR 12 B A N2QT 348,968 B B KB8UUZ 33,916 B B ND0C 36,698 B A KW7N 8,704

SEVERAL POINTS.  THE LOWEST FREQUENCY WILL BE THE FREQUENCY AT WHICH THE
LINE IS A HALF WAVELENGTH, THE NEXT WILL BE TWO HALF WAVELENGTHS, ETC.  THE
VELOCITY FACTOR CAN THEN BE CALCULATED BY THE RATIO OF THE PHYSICAL LINE
LENGTH TO THE VALUE OF A HALF WAVELENGTH IN VACUUM AT THE PARTICULAR
FREQUENCY GIVEN BY THE FORMULA L 492/F, WHERE L IS IN FEET AND F IS IN MHZ.
THE RESULTS FOR MY ROLL OF NO.  278 1385 SPEAKER WIRE NEAR FOUR AMATEUR
BANDS ARE SHOWN IN TABLE 1.  SINCE I PLANNED TO BUILD MY ANTENNAS MOSTLY
FOR THE 20 METER BAND AND ABOVE, I CHOSE TO USE 0R70 AS THE VELOCITY FACTOR
OF THIS LINE.  I COULD JUST AS WELL HAVE SAID THAT I PICKED 0R70 BECAUSE IT
IS A ROUND NUMBER OR BECAUSE IT IS APPROXIMATELY THE AVERAGE OF THE FOUR
READINGS.  I THINK THESE RESULTS ARE AMAZINGLY CONSISTENT CONSIDERING THE
USE OF A CONSUMER GRADE HANDHELD INSTRUMENT.  THERE IS ONLY A 4 VARIATION
IN MEASURED VELOCITY FACTOR OVER A FREQUENCY RANGE OF ABOUT AN ORDER OF
MAGNITUDE.  ATTENUATION THE ATTENUATION OR LINE LOSS WAS ALSO MEASURED
‰  FROM PAGE 81  ‰
607,005 A C K1DG 1,982,916 A C N5DX 1,389,545 A C KE9I 497,484 A C K5NA
1,249,620 A C K1LZ 1,787,478 A C W4AN 1,029,155 A C VE3XN 245,291 A C W5KFT

THE TYPE OF INSULATION USED ON THE RADIOSHACK SPEAKER WIRE ISNT SPECIFIED,
BUT I MADE THE ASSUMPTION THAT IT IS POLYETHYLENE OR A SIMILAR MATERIAL
THIS SEEMED SAFE SINCE MANY PLASTICS HAVE A SIMILAR DIELECTRIC CONSTANT OF
ABOUT 2R3.  IN ADDITION, SINCE THE INSULATION BETWEEN THE CONDUCTORS OF THE
SPEAKER WIRE IS THICKER PERPENDICULAR TO THE PLANE CONTAINING THE TWO WIRES
THAN THE INSULATION FOR 300 TWIN LEAD, IT SEEMED REASONABLE THAT IT MUST
HAVE A GREATER INFLUENCE ON THE CHARACTERISTIC IMPEDANCE SINCE MORE OF THE
FIELD BETWEEN THE CONDUCTORS WILL PASS THROUGH THE INSULATION AND LESS
THROUGH THE AIR.  BASED ON ALL OF THIS I ASSUMED THAT THE ADJUSTMENT FACTOR
FOR THE CHARACTERISTIC IMPEDANCE WOULD PROBABLY BE CLOSER TO 0R65 THAN TO
0R75, SO THE CHARACTERISTIC IMPEDANCE FOR THIS LINE MIGHT BE Z 224 X 0R65
145R6, OR ABOUT 150.  AGAIN, THIS VALUE IS NOT PARTICULARLY IMPORTANT, BUT
KEEP IT IN MIND AND WE WILL USE IT LATER TO ESTIMATE LINE LOSS.  VELOCITY
FACTOR THE VELOCITY FACTOR VF OF THE LINE WAS MEASURED USING THE VA1.  THE
TECHNIQUE INVOLVES SHORTING THE END OF THE LINE, THEN SWEEPING THE
INSTRUMENT OVER A RANGE OF FREQUENCIES TO FIND THE LOWEST IMPEDANCE AT
‰  FROM PAGE 81  ‰
193,533 A B VE7CC 964,626 A C KA1MDQ 20,800 A B W4KAZ 48,090 A B NR9A
143,226 A B K6XX 943,520 A C K3XO 46,926 A B VE3AT 1,930,480 A C VE4YU
141,030 A B K6AM 648,875 A C VY2ZM 2,339,922 A C VE3EJ 1,923,750 A C N6AN
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ