Double Extended Zepp NVIS Antenna Calculator

The measurements below are for building a Double Extended Zepp Near Vertical Incident Skywave (NVIS) Antenna. The Wire Size can range from 16 AWG to 12 AWG. The larger the wire, the wider the bandwidth.

The antenna is constructed much like an ordinary Dipole antenna but with 5/8 Wavelength Elements matched with an added Impedance Matching Section of balanced feed line. The Matching Section is 450 Ohm Open Wire Feedline and is a compromise impedance between the 5/8 Wave antenna elements and the feed point, A 4:1 Current Balun. The Balun on the end matches the 450 Ohm Open Wire Line into a 50 Ohm Coax Cable. The antenna as fed, matches reasonably well into a 50 Ohm Coax Cable Feedline.

A Ground Reflector can be added to enhance NVIS Propagation at frequencies below 10 MHz where NVIS Propagation is useable. 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 launch angle, antenna pattern, and propagation. This antenna is a great NVIS performer if you have the room for it.

Calculator
Frequency:  MHz

Please note: The calculations are approximate, so some exact antenna length and matching section 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 Extended Zepp Antenna NVIS Antenna Height Ground Reflector
  Element Length Ft (B) Matching Stub Length (C) Total Antenna Length (D) 1/8 Wave (E) 1/10 Wave (E) 1/20 Wave (E) Reflector Length (F)
160 Meters







1.8 350.00 57.22 700.00 65.00 52.00 26.00 735.00
1.9 331.58 54.21 663.16 61.58 49.26 24.63 696.32
2 315.00 51.50 630.00 58.50 46.80 23.40 661.50
80 Meters







3.5 180.00 29.43 360.00 33.43 26.74 13.37 378.00
3.6 175.00 28.61 350.00 32.50 26.00 13.00 367.50
3.7 170.27 27.84 340.54 31.62 25.30 12.65 357.57
3.8 165.79 27.11 331.58 30.79 24.63 12.32 348.16
3.9 161.54 26.41 323.08 30.00 24.00 12.00 339.23
4 157.50 25.75 315.00 29.25 23.40 11.70 330.75
60 Meters







5.3305 118.19 19.32 236.38 21.95 17.56 8.78 248.19 Ch1
5.3465 117.83 19.26 235.67 21.88 17.51 8.75 247.45 Ch2
5.3665 117.53 19.21 235.07 21.83 17.46 8.73 246.83 Ch3
5.3715 117.29 19.18 234.57 21.78 17.43 8.71 246.30 Ch4
5.4035 116.59 19.06 233.18 21.65 17.32 8.66 244.84 Ch5
40 Meters







7 90.00 14.71 180.00 16.71 13.37 6.69 189.00
7.03 89.68 14.66 179.36 16.65 13.32 6.66 188.33
7.13 88.42 14.46 176.84 16.42 13.14 6.57 185.68
7.16 87.99 14.39 175.98 16.34 13.07 6.54 184.78
7.18 87.80 14.36 175.61 16.31 13.05 6.52 184.39
7.3 86.30 14.11 172.60 16.03 12.82 6.41 181.23
30 Meters







10.1 62.38 10.20 124.75 11.58 9.27 4.63 130.99
10.15 62.07 10.15 124.14 11.53 9.22 4.61 130.34
20 Meters







14 45.00 7.36 90.00 8.36 6.69 3.34 94.50
14.1 44.68 7.30 89.36 8.30 6.64 3.32 93.83
14.2 44.37 7.25 88.73 8.24 6.59 3.30 93.17
14.23 44.29 7.24 88.58 8.22 6.58 3.29 93.01
14.3 44.06 7.20 88.11 8.18 6.55 3.27 92.52
14.35 43.90 7.18 87.80 8.15 6.52 3.26 92.20
17 Meters







18.07 34.87 5.70 69.74 6.48 5.18 2.59 73.22
18.11 34.79 5.69 69.57 6.46 5.17 2.58 73.05
18.17 34.68 5.67 69.35 6.44 5.15 2.58 72.82
15 Meters







21 30.00 4.90 60.00 5.57 4.46 2.23 63.00
21.1 29.86 4.88 59.72 5.55 4.44 2.22 62.70
21.2 29.72 4.86 59.43 5.52 4.42 2.21 62.41
21.3 29.58 4.84 59.15 5.49 4.39 2.20 62.11
21.45 29.37 4.80 58.74 5.45 4.36 2.18 61.68
12 Meters







24.89 25.31 4.14 50.62 4.70 3.76 1.88 53.15
24.99 25.21 4.12 50.42 4.68 3.75 1.87 52.94
10 Meters







28 22.50 3.68 45.00 4.18 3.34 1.67 47.25
28.5 22.11 3.61 44.21 4.11 3.28 1.64 46.42
29 21.72 3.55 43.45 4.03 3.23 1.61 45.62
29.7 21.21 3.47 42.42 3.94 3.15 1.58 44.55
30 21.00 3.43 42.00 3.90 3.12 1.56 44.10