On the weekend before last in the summer cottage, I unfolded (and turned) the antenna for the ranges of 7 and 14 MHz. But for the range of 3.5 MHz, the antenna is currently not. This article considers the antenna for the range of short waves 3.5 MHz.

Recently, I found an interesting version of the antenna antenna of anti -aircraft radiation (azi) from VE2DPE - Claude, but for the range 7 MHz, I decided to use this idea in the range of 3.5 MHz:
https://www.hamradiosecrets.com/nvis-Tenna.html

Introduction

Radio amateurs usually for ranges of 3.5 and 7 MHz put a mast of about 10 meters high in the center of the site and unfold on it the Inverted V antenna (see model with dimensions Invv.ma.zip). With a wavelength of 3.6 MHz, the full width of a curved in the form of an inverted letter V of the dipol is 36 meters. Dimensions of 36 meters - this is without taking into accounts. As he saidIn the last article about End Fed in the country, the summer cottage has a width of 20 and a length of 30 meters.

My attempts to count the VE2DPE antenna for a low-frequency range of 3.5 MHz (80 meters), but with an installation height of 2 meters and a 20 meters wide showed that the antenna will have a low input resistance (20-30 Ohms) due to proximity to Earth (relative height) and shortening by half (50%), its antenna has its antenna for the 40 range 40 meters are shortened by 37%. Therefore, in the model for the Mmana antennas modeling program, I tried to achieve a 3.5 MHz of the input resistance ** 50 ohms in the _ illegal_s of the antenna.

Starting conditions:
1) dimensions Antennas no more than 20 meters (if taken from the center. Then 10 meters left and 10 meters to the right)
2) Height supports for the antenna should be 2 meters (for example, fiberglass pipes from a construction store can be used as supports).

Option 1. Shortening of the dipole using train and bending the parties

IN version of Claude VE2DPE "A Portable NVIS Antenna for Field Work" в качестве полотна диполя для диапазона 40 метров использовался симметричный кабель 450 Ом.
The width of its antenna is 13.41 meters (44 ft) for the range 40 meters.
The symmetrical cable at the ends is closed, and in the center sed the (forms a "folded" dipole).

In my version, I decided that the antenna canvas should be from a single wire, because Be completely from a symmetrical cable to perform the antenna is wasteful. At the same time, in the edges of the antenna, put two short -closed loops, see drawing.

nvis.ma.zip
Antenna width 19.6 meters
Antenna height 2 meters
Input resistance 45 Ohms.
A strip of frequency at the level of KSV <2: 170 kHz
Strengthening -6.5 dB.

As you can see, the design with a train is quite complicated, although it allows you to configure the antenna by a change in two parameters: the length of the train and the length of the two bent "mustache" at the ends of the dipole.

Option 2. The edges of the dipole are collected in a loose accordion

In this embodiment, I refused the train. The wire to ensure resonance is collected at the ends of a shortened dipole in the accordion. The stretch of the canvas and the location of the wire "accordion" can be seen from the figure:

nvis2.ma.zip
Antenna width 19.6 meters
Antenna height 2 meters
Input resistance 51 Ohms.
A strip of frequencies in terms of KSV <2: 273 kHz
Strengthening -6.15 dB.

Option 3. The accordion along the edges of the dipole is compressed more tightly

nvis3.ma.zip
Antenna width 19.6 meters
Antenna height 2 meters
Input resistance 51 Ohms.
The resonance of the antenna shifted up significantly. (Antenna is sent)

Option 4. Simplification of the option 2. The accordion is replaced by inductance

Most of the folded dipole is replaced by a concentrated element - inductance.
Part of the accordion wire is left for configuration. Coils inductance - 39 mcg (select).

nvis4.ma.zip
Antenna width 19.6 meters
Antenna height 2 meters
Input resistance 58 Ohms.
A strip of frequency at the level of KSV <2: 70 kHz
Strengthening -6.25 dB.
The antenna with inductances came out narrow -band.

Option 5. Simplification of option 4. Inductance + bent wire

Most of the folded dipole is replaced by a concentrated element - inductance.
Part of the accordion wire is left for configuration. Coils inductance - 39 mcg (select).

nvis5.ma.zip
Antenna width 19.6 meters
Antenna height 2 meters
Input resistance 50 Ohms.
A strip of frequency at the level of KSV <2: 70 kHz
Strengthening -6.17 dB.
The antenna with inductances again came out narrow -band.

Option 6. The Inverted V Antenna on a low mast, with bent edges

NVIS6.MAA.ZIP
Antenna width 20 meters
Antenna height 3 meters
Input resistance 42 Ohms.
A strip of frequency at the level of KSV <2: 150 kHz
Strengthening -5.11 dB .
The antenna came out quite broadband. The reinforcement factor is 1 dB higher than that of other options.

Option 7. A simple dipole of 20 m wide, on a low mast, with bent edges

NVIS7.MAA.zip
Antenna width 20 meters
Antenna height 2 meters
Input resistance 42 Ohms.
A strip of frequency at the level of KSV <2: 160 kHz
Strengthening -6.3 dB.
The antenna in a linear configuration came out quite broadband.

Option 8. A simple dipole on a low mast, with bent edges. The width is 26 meters

nvis8.ma.zip
Antenna width 26 meters
Antenna height 2 meters
Input resistance 45 Ohms.
A strip of frequency at the level of KSV <2: 160 kHz
Strengthening -4.4 db.
The antenna in a linear configuration came out quite broadband. Strengthening when extended by 6 meters increased by 2 dB .

Conclusions

The best options for NVIS Antennas for limited space by the criterion of the most wide work band (BW)

1) Option 2. The edges of a shortened dipole are collected in a loose accordion.
2) Option 8. A simple dipole on a low mast, with bent edges. The width of the antenna -rendered from 20 to 26 meters.
3) Option 7. A simple dipole on a low mast, with bent edges
4) Option 6. The Inverted V Antenna on a low mast, with bent edges
5) Option 1. Shortening of the dipole using train and bending the parties

Narrow -lane antennas - with inductances in the canvas: No. 4 and No. 5.

According to the reinforcement factor

1) The best option is No. 8 (a dipole with bent edges, R = 45 Ohms, BW = 160 kHz), the length of the antenna is 26 meters (strengthening G = -4.4 dB).
2) Option No. 6 : inverted v on a low mast with bent edges, r = 42 Ohms, bW = 150 kHz), antenna dimensions 20 meters (amplification G = -5.1 dB).
3) Option No. 7 Low hanging dipole with bent ends, antenna width 20 meters, BW = 160 kHz (amplification G = -6.3 dB). Antenna is inferior in reinforcement due to the low height of the power point and shortening 20 <26 meters .

Scheme. Two antennas, full -sized Inverted V and option No. 6 , side view. Green marks the boundary of the site on the largest side (30 meters).

Dimensions of the antenna option No. 6:

• total wire length (7+1.7+9.85) * 2 = 37.1 meter

• upper inclined shoulders antenna - 2 to 9.85 meters

• Side vertical sides, 1.7 meters

• Lower bent segments of 7 meters (at an altitude of 0.3 m).

• The upper point of the canvas of the antenna is 3 meters.

  Dimensions of the antenna option No. 8:

• total wire length 41 meters (26+13+2)

• The upper part of the fabric of the antenna 26 m long

• Side sides 1 m

• Lower bent segments at 6.5 m (at a height of 1 m).

• The height of the top of the canvas of the antenna canvas is 2 meters.

Links:

• Portable nvis antenna - portable azi
• Mmana Gal Basic - Antennas Modeling Program
• Mmana rus - a program for modeling antennas
• Nec2 for mmana - engine for calculating the models of wire antennas in mmana format, taking into account shortening of the wire, close arrangement of the antenna to the Earth's surface.

Last change: 01.03.2025: correction in the paragraph about conclusions .

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