Double Bazooka NVIS Antenna Calculator

The measurements below are for building a Double Bazooka Near Vertical Incident Skywave (NVIS) Antenna. The End Wire Size can range from 16 AWG to 12 AWG. The larger the wire, the wider the bandwidth. 300 Ohm Twin Lead with the ends shorted is an option for even greater bandwidth.

The antenna is constructed from a single length of 50 or 75 Ohm coax with a coaxial feed point in the center. The span is opened in the middle to expose the braid from each half. The center conductor and dielectric is not disturbed and the two separated braids are then fed with the Coax Feedline. Each end of the coaxial span has the braid and center conductor shorted and connected to the end wires.

The antenna as designed is a broad band antenna with the coaxial cable's capacitive reactance changing to compensate for changes in inductive reactance across the band of operation. This helps to provide acceptable matches on frequencies other than what the antenna was specifically designed for. The antenna as fed matches reasonably well into a 50 Ohm Coax Cable Feedline and an antenna tuner.

A Ground Reflector can be added to enhance NVIS Propagation at frequencies below 10 MHz where NVIS Propagation is usable. The Ground Reflector can be a single conductor or several in parallel spaced a few feet apart. Hardware cloth or "Poultry Screening" is an option too. Several antenna / reflector elevation options are shown that enhance the NVIS vertical antenna pattern and propagation.

Calculator
Frequency:  MHz

Please note: The calculations are approximate, so some final end wire length adjustment may be necessary. Dimensions will change slightly due to antenna height and ground conductivity variations...and Keep The Antenna Away From Power Lines. They are good at turning you into "The Squirrel in the Substation".

Antenna Diagram

Please note: NVIS Propagation is only useful at frequencies below 10 MHz.

   

Double Bazooka Antenna NVIS Antenna Height Ref Dipole



  End Wire Length Ft (B) Coax Element Length (C) Coaxial Element Center (D) Total Length Ft (E) 0.1 Wave 1/8 Wave 1/20 Wave Reflector Length 1/2 Wave Ft
160 Meters








1.8 37.50 180.56 90.28 255.56 52.00 65.00 26.00 268.33 260.00
1.9 35.53 171.05 85.53 242.11 49.26 61.58 24.63 254.21 246.32
2 33.75 162.50 81.25 230.00 46.80 58.50 23.40 241.50 234.00
80 Meters








3.5 19.29 92.86 46.43 131.43 26.74 33.43 13.37 138.00 133.71
3.6 18.75 90.28 45.14 127.78 26.00 32.50 13.00 134.17 130.00
3.7 18.24 87.84 43.92 124.32 25.30 31.62 12.65 130.54 126.49
3.8 17.76 85.53 42.76 121.05 24.63 30.79 12.32 127.11 123.16
3.9 17.31 83.33 41.67 117.95 24.00 30.00 12.00 123.85 120.00
4 16.88 81.25 40.63 115.00 23.40 29.25 11.70 120.75 117.00
60 Meters








5.3305 12.66 60.97 30.48 86.30 17.56 21.95 8.78 92.19 87.80 Ch1
5.3465 12.63 60.79 30.39 86.04 17.51 21.88 8.75 91.91 87.53 Ch2
5.3665 12.58 60.56 30.28 85.72 17.44 21.80 8.72 91.57 87.21 Ch3
5.3715 12.57 60.50 30.25 85.64 17.43 21.78 8.71 91.48 87.13 Ch4
5.4035 12.49 60.15 30.07 85.13 17.32 21.65 8.66 90.94 86.61 Ch5
40 Meters








 
7 9.64 46.43 23.21 65.71 13.37 16.71 6.69 69.00 66.86
7.1 9.51 45.77 22.89 64.79 13.18 16.48 6.59 68.03 65.92
7.15 9.44 45.45 22.73 64.34 13.09 16.36 6.55 67.55 65.45
7.2 9.38 45.14 22.57 63.89 13.00 16.25 6.50 67.08 65.00
7.3 9.25 44.52 22.26 63.01 12.82 16.03 6.41 66.16 64.11
30 Meters








10.1 6.68 32.18 16.09 45.54 9.27 11.58 4.63 47.82 46.34
10.15 6.65 32.02 16.01 45.32 9.22 11.53 4.61 47.59 46.11
20 Meters








14 4.82 23.21 11.61 32.86 6.69 8.36 3.34 34.50 33.43
14.1 4.79 23.05 11.52 32.62 6.64 8.30 3.32 34.26 33.19
14.2 4.75 22.89 11.44 32.39 6.59 8.24 3.30 34.01 32.96
14.22 4.75 22.86 11.43 32.35 6.58 8.23 3.29 33.97 32.91
14.3 4.72 22.73 11.36 32.17 6.55 8.18 3.27 33.78 32.73
14.31 4.72 22.71 11.35 32.14 6.54 8.17 3.27 33.75 32.70
17 Meters








18.07 3.74 17.99 8.99 25.46 5.18 6.48 2.59 26.73 25.90
18.13 3.72 17.93 8.96 25.37 5.16 6.45 2.58 26.64 25.81
15 Meters








21 3.21 15.48 7.74 21.90 4.46 5.57 2.23 23.00 22.29
21.1 3.20 15.40 7.70 21.80 4.44 5.55 2.22 22.89 22.18
21.2 3.18 15.33 7.67 21.70 4.42 5.52 2.21 22.78 22.08
21.3 3.17 15.26 7.63 21.60 4.39 5.49 2.20 22.68 21.97
12 Meters








24.89 2.71 13.06 6.53 18.48 3.76 4.70 1.88 19.41 18.80
24.95 2.71 13.03 6.51 18.44 3.75 4.69 1.88 19.36 18.76
10 Meters








28 2.41 11.61 5.80 16.43 3.34 4.18 1.67 17.25 16.71
28.5 2.37 11.40 5.70 16.14 3.28 4.11 1.64 16.95 16.42
29 2.33 11.21 5.60 15.86 3.23 4.03 1.61 16.66 16.14
29.5 2.29 11.02 5.51 15.59 3.17 3.97 1.59 16.37 15.86