We shall feed the 102' wire with parallel transmission line all the way to the ATU. With this feed system, the exact length is not critical ±5' or so. The patterns will be mostly unaffected, but variations in length and height will change the feedpoint resistance and reactance more significantly.
100' flattops or doublets have been used as long as any old timer remembers. The precise 102' length became famous when G5RV developed a feed system that he hoped would allow hams to use the antenna on harmonically related bands with about 33' of 450-ohms line or 29' of 300- ohms line, and the rest 50-ohms coax. Two problems changed fame into controversy. First, the WARC bands opened, adding nonharmonically related frequencies to the multiband antenna wish list. Second, on the low bands, small changes of length and height alter the feedpoint impedance, thus disrupting the low SWR match effected by the parallel line lengths.
But the 102' doublet (= any center-fed wire) does work well with parallel line all the way to the ATU. However, its patterns and impedances along parallel transmission line differ from those of the 135' dipole. Therefore, the 102' antenna deserves a data compendium of its own.
See the preceding installment of this series for instructions on interpreting the patterns and the feedline impedance tables, along with the method for calculating the ballpark impedance presented to your own ATU.
The line impedances are calculated from the feedpoint impedance of the NEC- 2 model of the antenna at a 50' height. For intermediate values at 5 deg. intervals, see the transmission line performance program in HAMCALC. If you need values that account for line loss, ARRL's N6BV has written a fine program, but it calculates one value at a time.
The impedance values are intended only as indicators of the magnitude of resistance and reactance and the rising or falling direction of those magnitudes along the line. The accuracy of the values for any given ham installation, with its typical domestic "clutter," is no more than about 20%, considering variations in height and antenna length. At most, they can tell you that a longer or a shorter line might be better for a given band. In other words, they can suggest why your tuner may be having difficulties in matching the antenna on a given band. It is usually cheaper to add a little line length than to add a new tuner to the system.
80 meters: 3.6 MHz AZ plots: Elevation angles = 45 deg. EL plots: Azimuth angles = 90 deg. Feedpoint Z (R ± jX): 35 - 420 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 35 - 420 20 14.4 4.4 20 - 190 40 28.8 8.8 20 - 25 60 43.3 13.2 20 + 135 80 57.7 17.6 30 + 335 100 72.1 22.0 60 + 685 120 86.5 26.4 350 + 1870 140 101.0 30.8 1165 - 3330 160 115.4 35.2 90 - 880 180 129.8 39.6 35 - 420 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 35 - 420 20 12.1 3.7 15 - 205 40 24.3 7.4 15 - 80 60 36.4 11.1 10 + 30 80 48.6 14.8 15 + 140 100 60.7 18.5 25 + 305 120 72.9 22.2 70 + 650 140 85.0 25.9 1475 + 3010 160 97.1 29.6 165 - 1065 180 109.3 33.3 35 - 420
40 meters: 7.15 MHz AZ plots: El. Angle = 45 deg. @ 35'; 39 deg. @ 50' EL plots: Az. Angles = 90 deg. Feedpoint Z (R ± jX): 450 + 1045 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 450 + 1045 20 7.3 2.2 3260 + 150 40 14.5 4.4 480 - 1075 60 21.8 6.6 150 - 520 80 29.0 8.9 85 - 255 100 36.3 11.1 65 - 80 120 43.6 13.3 65 + 75 140 50.8 15.5 80 + 250 160 58.1 17.7 145 + 505 180 65.3 19.9 450 + 1045 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 450 + 1045 20 6.1 1.9 1380 - 1500 40 12.2 3.7 145 - 580 60 18.3 5.6 55 - 280 80 24.5 7.5 35 - 130 100 30.6 9.3 30 - 20 120 36.7 11.2 30 + 85 140 42.8 13.0 45 + 215 160 48.9 14.9 95 + 435 180 55.0 16.8 450 + 1045
30 meters: 10.125 MHz AZ plots: El. Angle = 39 deg. @ 35'; 27 deg. @ 50' EL plots: Az. Angles = 90 deg. Feedpoint Z (R ± jX): 2220 - 3200 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 2220 - 3200 20 5.1 1.6 155 - 925 40 10.3 3.1 60 - 440 60 15.4 4.7 35 - 205 80 20.5 6.3 30 - 35 100 25.6 7.8 30 + 125 120 30.8 9.4 45 + 320 140 35.9 10.9 90 + 645 160 41.0 12.5 435 + 1625 180 46.1 14.1 2220 - 3200 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 2220 - 3200 20 4.3 1.3 80 - 680 40 8.6 2.6 30 - 315 60 13.0 4.0 15 - 150 80 17.3 5.3 15 - 35 100 21.6 6.6 15 + 75 120 25.9 7.9 20 + 200 140 30.2 9.2 35 + 405 160 34.5 10.5 160 + 995 180 38.9 11.8 2220 - 3200
20 meters: 14.15 MHz AZ plots: El. Angle = 26 deg. @ 35'; 19 deg. @ 50' EL plots: Az. Angles = 37 deg. @ 35' 40 deg. @ 50' Feedpoint Z (R ± jX): 100 - 50 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 100 - 50 20 3.8 1.1 105 + 100 40 7.3 2.2 140 + 275 60 11.0 3.4 60 - 270 80 14.7 4.5 780 + 930 100 18.3 5.6 1920 - 485 120 22.0 6.7 500 - 790 140 25.7 7.8 200 - 430 160 29.4 9.0 120 - 215 180 33.0 10.1 100 - 50 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 100 - 50 20 3.1 0.9 100 + 45 40 6.2 1.9 125 + 145 60 9.3 2.8 200 + 275 80 12.4 3.8 450 + 410 100 15.5 4.7 925 + 25 120 18.5 5.7 475 - 40 140 21.6 6.6 210 - 285 160 24.7 7.5 125 - 155 180 27.8 8.5 100 - 50
17 meters: 18.1 MHz AZ plots: El. Angle = 21 deg. @ 35'; 15 deg. @ 50' EL plots: Az. Angles = 54 deg. @ 35' 54 deg. @ 50' Feedpoint Z (R ± jX): 2040 + 1640 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 2040 + 1640 20 2.9 0.9 815 - 1400 40 5.7 1.8 185 - 635 60 8.6 2.6 90 - 320 80 11.5 3.5 65 - 130 100 14.3 4.4 60 + 30 120 17.2 5.2 70 + 195 140 20.1 6.1 110 + 415 160 22.9 7.0 285 + 835 180 25.8 7.9 2040 + 1640 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 2040 + 1640 20 2.4 0.7 325 - 955 40 4.8 1.5 75 - 405 60 7.3 2.2 40 - 200 80 9.7 2.9 30 - 75 100 12.1 3.7 25 + 30 120 14.5 4.4 30 + 145 140 16.9 5.2 55 + 305 160 19.3 5.9 155 + 640 180 21.7 6.6 2040 + 1640
15 meters: 21.15 MHz AZ plots: El. Angle = 18 deg. @ 35'; 13 deg. @ 50' EL plots: Az. Angles = 60 deg. @ 35' 61 deg. @ 50' Feedpoint Z (R ± jX): 375 - 1135 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 375 - 1135 20 2.5 0.8 115 - 525 40 4.9 1.5 65 - 255 60 7.4 2.2 50 - 80 80 9.8 3.0 50 + 80 100 12.3 3.7 65 + 255 120 14.7 4.5 110 + 520 140 17.2 5.2 370 + 1125 160 19.6 6.0 4300 + 75 180 22.1 6.7 375 - 1135 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 375 - 1135 20 2.1 0.6 75 - 445 40 4.1 1.3 35 - 220 60 6.2 1.9 25 - 90 80 8.3 2.5 20 + 20 100 10.3 3.2 25 + 130 120 12.4 3.8 40 + 280 140 14.5 4.4 110 + 585 160 16.5 5.0 1215 + 1830 180 18.6 5.7 375 - 1135
12 meters: 24.95 MHz AZ plots: El. Angle = 15 deg. @ 35'; 11 deg. @ 50' EL plots: Az. Angles = 34 deg. @ 35' 35 deg. @ 50' Feedpoint Z (R ± jX): 205 + 335 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 205 + 335 20 2.1 0.6 415 + 590 40 4.2 1.3 1215 + 660 60 6.2 1.9 1160 - 685 80 8.3 2.5 400 - 575 100 10.4 3.2 200 - 325 120 12.5 3.8 140 - 145 140 14.6 4.4 125 + 5 160 16.6 5.1 140 + 155 180 18.7 5.7 205 + 335 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 205 + 335 20 1.8 0.5 560 + 515 40 3.5 1.1 1050 - 240 60 5.3 1.6 360 - 460 80 7.0 2.1 155 - 270 100 8.8 2.7 100 - 135 120 10.5 3.2 80 - 30 140 12.3 3.7 85 + 70 160 14.0 4.3 115 + 180 180 15.8 4.8 205 + 335
10 meters: 28.5 MHz AZ plots: El. Angle = 14 deg. @ 35'; 10 deg. @ 50' EL plots: Az. Angles = 44 deg. @ 35' 44 deg. @ 50' Feedpoint Z (R ± jX): 3235 - 65 ohms TL = 450 ohms; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 3235 - 65 20 1.8 0.6 460 - 1050 40 3.6 1.1 145 - 510 60 5.5 1.7 80 - 250 80 7.3 2.2 65 - 75 100 9.1 2.8 65 + 80 120 10.9 3.3 85 + 255 140 12.8 3.9 150 + 515 160 14.6 4.4 475 + 1065 180 16.4 5.0 3235 - 65 TL = 300 ohms; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 3235 - 65 20 1.5 0.5 220 - 765 40 3.1 0.9 65 - 350 60 4.6 1.4 35 - 170 80 6.1 1.9 30 - 50 100 7.7 2.3 30 + 55 120 9.2 2.8 35 + 170 140 10.7 3.3 65 + 350 160 12.3 3.7 225 + 770 180 13.8 4.2 3235 - 65
Updated 9-1-97. © L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.