ANTENNAS FROM THE GROUND UP
It is important to understand that the pattern of lobes and nulls varies with each band. This information is useful for orienting the antenna and for properly anticipating performance. The precise length of the antenna between 130' and 140' will have little effect on the individual band patterns.
Changes of length will have a more profound effect upon the feedpoint impedance, as will changes of height. In contrast, changes of wire diameter between AWG #18 and #10 will have little noticeable effect.
The pages to follow are designed to allow the antenna builder to have some reasonable expectations both for antenna patterns and for impedances presented to the ATU by the antenna and its feedline. Each column in the following pages is devoted to the performance of the antenna on one of the HF bands from 80 to 10 meters. For each band there is a composite pattern plot and a pair of tables.
The patterns show NEC-2 plots of the antenna at heights of 35' and 50'. The 35' pattern is always the inner or weaker of the two patterns. If the angle of maximum radiation is greater than 45°, then the azimuth pattern is taken at an elevation angle of 45°. If the angle of maximum radiation is less than 45°, then the take-off angle is used. The elevation patterns are taken at the azimuth angle of the strongest lobe. Therefore, interpreting the patterns requires that you consider azimuth and elevation together.
The tables list, in highly rounded numbers, the impedance presented along parallel transmission lines every 20° (electrical) for a half wavelength. Standard 450-ohm (Velocity Factor = 0.95) and 300-ohm (VF = 0.80) lines are given. Note that each electrical degree represents a different length in feet and meters for each band and line type. Values are for lossless lines from the 50' high antenna.
Since impedance values repeat themselves every 180° along a feedline, you may estimate (very broadly at best) the impedance presented to your ATU. Divide the length in feet or meters of your transmission line by the length of a half wavelength (180°) of the same line. Ignore the integer and multiply the fraction of a half wavelength by 180 to arrive at the value in degrees to check against the applicable table.
80 meters: 3.6 MHz AZ plots: Elevation angles = 45° EL plots: Azimuth angles = 90° Feedpoint Z (R ± jX): 75 + 55 ohms TL = 450 ohm; VF = .95 Deg Feet Meters R ± jX (ohms) 0 0 0 75 + 55 20 14.4 4.4 95 + 220 40 28.8 8.8 155 + 455 60 43.3 13.2 420 + 890 80 57.7 17.6 2450 + 770 100 72.1 22.0 680 - 1107 120 86.5 26.4 200 - 555 140 101.0 30.8 105- 280 160 115.4 35.2 80 - 100 180 129.8 39.6 75 + 55 TL = 300 ohm; VF = .80 Deg Feet Meters R ± jX (ohms) 0 0 0 75 + 55 20 12.1 3.7 95 + 165 40 24.3 7.4 170 + 315 60 36.4 11.1 450 + 540 80 48.6 14.8 1220 - 55 100 60.7 18.5 415 - 525 120 72.9 22.2 160 - 305 140 85.0 25.9 95 - 155 160 97.1 29.6 75 - 45 180 109.3 33.3 75 + 55
40 meters: 7.15 MHz
AZ plots: El. Angle = 45° @ 35';
39° @ 50'
EL plots: Az. Angles = 90°
Feedpoint Z (R ± jX): 4760 - 1270 ohms
TL = 450 ohms; VF = .95
Deg Feet Meters R ± jX (ohms)
0 0 0 4760 - 1270
20 7.3 2.2 285 - 1085
40 14.5 4.4 90 - 500
60 21.8 6.6 50 - 245
80 29.0 8.9 40 - 70
100 36.3 11.1 40 + 90
120 43.6 13.3 55 + 270
140 50.8 15.5 100 + 550
160 58.1 17.7 365 + 1240
180 65.3 19.9 4760 - 1270
TL = 300 ohms; VF = .80
Deg Feet Meters R ± jX (ohms)
0 0 0 4760 - 1270
20 6.1 1.9 135 - 765
40 12.2 3.7 40 - 345
60 18.3 5.6 25 - 165
80 24.5 7.5 20 - 50
100 30.6 9.3 18.3 + 60
120 36.7 11.2 25 + 180
140 42.8 13.0 45 + 365
160 48.9 14.9 160 + 840
180 55.0 16.8 4760 - 1270
30 meters: 10.125 MHz
AZ plots: El. Angle = 39° @ 35';
27° @ 50'
EL plots: Az. Angles = 90°
Feedpoint Z (R ± jX): 95 - 330 ohms
TL = 450 ohm; VF = .95
Deg Feet Meters R ± jX (ohms)
0 0 0 95 - 330
20 5.1 1.6 65 - 135
40 10.3 3.1 60 + 20
60 15.4 4.7 70 + 185
80 20.5 6.3 110 + 405
100 25.6 7.8 270 + 805
120 30.8 9.4 1805 + 1645
140 35.9 10.9 910 - 1445
160 41.0 12.5 195 - 655
180 46.1 14.1 95 - 330
TL = 300 ohms; VF = .80
Deg Feet Meters R ± jX (ohms)
0 0 0 95 - 330
20 4.3 1.3 55 - 165
40 8.6 2.6 40 - 45
60 13.0 4.0 40 + 55
80 17.3 5.3 55 + 175
100 21.6 6.6 100 + 350
120 25.9 7.9 330 + 730
140 30.2 9.2 2160 - 230
160 34.5 10.5 290 - 685
180 38.9 11.8 95 - 330
20 meters: 14.15 MHz
AZ plots: El. Angle = 27° @ 35';
19° @ 50'
EL plots: Az. Angles = 52° @ 35'
55° @ 50'
Feedpoint Z (R ± jX): 4270 - 1005 ohms
TL = 450 ohm; VF = .95
Deg Feet Meters R ± jX (ohms)
0 0 0 4270 - 1005
20 3.8 1.1 405 - 1215
40 7.3 2.2 115 - 550
60 11.0 3.4 60 - 270
80 14.7 4.5 45 - 90
100 18.3 5.6 45 + 70
120 22.0 6.7 60 + 240
140 25.7 7.8 100 + 500
160 29.4 9.0 320 + 1070
180 33.0 10.1 4270 + 1005
TL = 300 ohm; VF = .80
Deg Feet Meters R ± jX (ohms)
0 0 0 4270 - 1005
20 3.1 0.9 180 - 830
40 6.2 1.9 50 - 365
60 9.3 2.8 25 - 180
80 12.4 3.8 20 - 60
100 15.5 4.7 20 + 50
120 18.5 5.7 25 + 165
140 21.6 6.6 45 + 345
160 24.7 7.5 150 + 760
180 27.8 8.5 4270 - 1005
17 meters: 18.1 MHz
AZ plots: El. Angle = 19° @ 35';
14° @ 50'
EL plots: Az. Angles = 29° @ 35'
30° @ 50'
Feedpoint Z (R ± jX): 125 + 5 ohms
TL = 450 ohm; VF = .95
Deg Feet Meters R ± jX (ohms)
0 0 0 125 + 5
20 2.9 0.9 145 + 155
40 5.7 1.8 205 + 335
60 8.6 2.6 420 + 585
80 11.5 3.5 1210 + 645
100 14.3 4.4 1155 - 670
120 17.2 5.2 400 - 575
140 20.1 6.1 205 - 325
160 22.9 7.0 140 - 145
180 25.8 7.9 125 + 5
TL = 300 ohm; VF = .80
Deg Feet Meters R ± jX (ohms)
0 0 0 125 + 5
20 2.4 0.7 140 + 90
40 4.8 1.5 195 + 185
60 7.3 2.2 340 + 280
80 9.7 2.9 635 + 195
100 12.1 3.7 610 - 215
120 14.5 4.4 320 - 275
140 16.9 5.2 190 - 180
160 19.3 5.9 140 - 85
180 21.7 6.6 125 + 5
15 meters: 21.15 MHz
AZ plots: El. Angle = 18° @ 35';
13° @ 50'
EL plots: Az. Angles = 41° @ 35'
43° @ 50'
Feedpoint Z (R ± jX): 2330 + 1435 ohms
TL = 450 ohms; VF = .95
Deg Feet Meters R ± jX (ohms)
0 0 0 2330 + 1435
20 2.5 0.8 735 - 1300
40 4.9 1.5 185 - 605
60 7.4 2.2 90 - 305
80 9.8 3.0 65 - 120
100 12.3 3.7 65 + 40
120 14.7 4.5 75 + 205
140 17.2 5.2 125 + 435
160 19.6 6.0 320 + 870
180 22.1 6.7 2330 + 1435
TL = 300 ohm; VF = .80
Deg Feet Meters R ± jX (ohms)
0 0 0 2330 + 1435
20 2.1 0.6 310 - 905
40 4.1 1.3 75 - 395
60 6.2 1.9 40 - 195
80 8.3 2.5 30 - 70
100 10.3 3.2 30 + 35
120 12.4 3.8 35 + 150
140 14.5 4.4 60 + 310
160 16.5 5.0 170 + 660
180 18.6 5.7 2330 + 1435
12 meters: 24.95 MHz
AZ plots: El. Angle = 14° @ 35';
10° @ 50'
EL plots: Az. Angles = 23° @ 35'
24° @ 50'
Feedpoint Z (R ± jX): 130 - 180 ohms
TL = 450 ohm; VF = .95
Deg Feet Meters R ± jX (ohms)
0 0 0 130 - 180
20 2.1 0.6 110 - 25
40 4.2 1.3 120 + 130
60 6.2 1.9 170 + 305
80 8.3 2.5 325 + 565
100 10.4 3.2 1020 + 855
120 12.5 3.8 1490 - 675
140 14.6 4.4 440 - 670
160 16.6 5.1 200 - 375
180 18.7 5.7 130 - 180
TL = 300 ohm; VF = .80
Deg Feet Meters R ± jX (ohms)
0 0 0 130 - 180
20 1.8 0.5 100 - 70
40 3.5 1.1 95 + 25
60 5.3 1.6 110 + 125
80 7.0 2.1 170 + 250
100 8.8 2.7 370 + 410
120 10.5 3.2 920 + 205
140 12.3 3.7 575 - 440
160 14.0 4.3 230 - 320
180 15.8 4.8 130 - 180
10 meters: 28.5 MHz
AZ plots: El. Angle = 13° @ 35';
10° @ 50'
EL plots: Az. Angles = 36° @ 35'
37° @ 50'
Feedpoint Z (R ± jX): 2070 + 1225 ohms
TL = 450 ohms; VF = .95
Deg Feet Meters R ± jX (ohms)
0 0 0 2070 + 1225
20 1.8 0.6 835 - 1230
40 3.6 1.1 215 - 605
60 5.5 1.7 105 - 310
80 7.3 2.2 75 - 120
100 9.1 2.8 70 + 35
120 10.9 3.3 85 + 200
140 12.8 3.9 135 + 420
160 14.6 4.4 345 + 825
180 16.4 5.0 2070 + 1225
TL = 300 ohms; VF = .80
Deg Feet Meters R ± jX (ohms)
0 0 0 2070 + 1225
20 1.5 0.5 360 - 895
40 3.1 0.9 90 - 395
60 4.6 1.4 45 - 195
80 6.1 1.9 35 - 70
100 7.7 2.3 30 + 35
120 9.2 2.8 40 + 145
140 10.7 3.3 65 + 305
160 12.3 3.7 190 + 640
180 13.8 4.2 2070 + 1225
Updated 7-1-97. © 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.
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