Systematic Investigation of a large fixed 145 MHz Yagi Group

The following investigations have been performed to lay the base for a larger group of yagis for the 145 MHz band to be used for contest operation at mount Schneeberg, JO50WB. It has been inspired by the antenna group used by the DR9A contest group at their portable contest QTH. Mount Schneeberg is the highest peak of the Fichtelgebirge located in the northern part of Bavaria close to the Czech border. It is very demanding with respect to weather condition and high-frequency environment. Antennas will have to be setup in spring and removed in autumn since they won’t survive the winter storms.

Acknowledgements

I would like to thank the following persons for their extensive and unconditional support:

  • Martin, DK7ZB: for developing the single antennas and adapting them to our needs
  • Henning, DF9IC: for sharing its enormous technical expertise with an advanced beginner

In addition there has been support by solving smaller problems with the simulation environment or understanding the results obtained by

  • Peter, DL2NBU
  • Sigi, DL8NAS
  • Hubert, DK3RU

Introduction

The Goal

Antenna group to be used during contest operation with the following characteristics:

  • omni-directional radiation pattern
  • reasonable gain
  • to be mounted on a portable surplus mast (lowered to ground during non-contest periods)

Technical Solution

  • several individual groups of four 5 or 6-element antennas vertically stacked
  • individual groups distributed horizontally
  • mast side mounting of the individual antennas

Simulation Environment

All simulations have been performed with the following simulation environment:

  • HP Workstation W3520 @2.67GHz
  • 16GB RAM
  • Windows 7
  • 4Nec2 Version 5.9.3
    • maximum number of ‘EX cards’ increased to 36
    • maximum number of ‘LD cards’ increased to more than 192

Single Yagi Survey

Antennas under Survey

Antennas with a maximum of about 2.5 m overall boom length and reasonable gain to horizontal beam width value have been considered for the project. Thus, the following 5- and 6-element DK7ZB antennas have been investigated:

DescriptionRefDEDir #1Dir #2Dir #3Dir #4
5-el 28Ohm OWM YagiPosition [mm]031554510251480--
Length [mm]1024983939927896--
6-el 28Ohm OWM YagiPosition [mm]027542084014952065
Length [mm]10201000959917911871
5-el 28Ohm YagiPosition [mm]035071012951780--
Length [mm]1022962919914885--
6-el 28Ohm YagiPosition [mm]0390640115017852380
Length [mm]1017971935907905876

The geometrical data of all antennas has been taken from the web page of DK7ZB (https://dk7zb.darc.de/) or obtained by private communication.

Results

DK7ZB 5-Element Antenna (l = 1.78 m)

4NEC2 Input:Geometry File
Frequency:144.3 MHz
Impedance:(27.7 - j 0.6) Ω
Gain:11.1 dBi
F/B:20 db
Radiation Pattern:horizontal:
Invalid shortcode
3dB-Angle: 48°		vertical:
Invalid shortcode
3dB-Angle: 60°

DK7ZB 5-Element OWM Antenna (l = 1.48 m)

4NEC2 Input:Geometry File
Frequency:144.3 MHz
Impedance:(27.3 - j 1.0) Ω
Gain:10.5 dBi
F/B:30 db
Radiation Pattern:horizontal:
Invalid shortcode
3dB-Angle: 50°		vertical:
Invalid shortcode
3dB-Angle: 64°

DK7ZB 6-Element Antenna (l = 2.40 m)

4NEC2 Input:Geometry File
Frequency:145.0 MHz
Impedance:(32.5 + j 0.7) Ω
Gain:12.1 dBi
F/B:23 db
Radiation Pattern:horizontal:
Invalid shortcode
3dB-Angle: 44°		vertical:
Invalid shortcode
3dB-Angle: 52°

DK7ZB 6-Element OWM Antenna (l = 2.07 m)

4NEC2 Input:Geometry File
Frequency:144.3 MHz
Impedance:(27.8 + j 0.7) Ω
Gain:11.5 dBi
F/B:38 db
Radiation Pattern:horizontal:
Invalid shortcode
3dB-Angle: 48°		vertical:
Invalid shortcode
3dB-Angle: 58°

Note: This antenna has been advertised as a 28Ω-Yagi. However simulations show a radiation resistance of about 33 Ω in resonance. However, this won’t be further investigated since this antenna won’t be of interest in this project. See further down for details.

Discussion

The slightly higher gain of the standard yagis results in a radiation pattern with increased side lobes and larger mechanical dimensions. So, it seems that the OWM-yagis will be more promising with respect to the goal of the project.

The 6-element standard yagi will be excluded completely from further investigations since the mechanical length of almost 2.5 m poses a great challenge in pre-mast mounting.

Vertical Stacking

The mechanical length of the antennas of interest are all about in the range of about an wave length. Thus, the standard DL6WU formula would fail for the determination of an optimal vertical stacking distance. So, simulations have been carried to characterize the resulting antenna stacks as function of the stacking distance.

DK7ZB 5-Element Antenna (l = 1.78 m)

4NEC2 Input:Geometry File
Frequency:144.3 MHz
Stacking DistanceHorizontal PatternVertical Pattern
h = 1.80 m

Impedance: (25.2+ j 3.7) Ω
Gain: 15.8 dBi
F/B: 16 dB		Invalid shortcode
3dB-Angle: 46°		Invalid shortcode
3dB-Angle: 14°
h = 1.90 m

Impedance: (28.7 + j 3.3) Ω
Gain: 16.3 dBi
F/B: 28 dB		Invalid shortcode
3dB-Angle: 48°		Invalid shortcode
3dB-Angle: 14°
h = 2.00 m

Impedance: (30.1 + j 1.4) Ω
Gain: 16.7 dBi
F/B: 27 dB		Invalid shortcode
3dB-Angle: 50°		Invalid shortcode
3dB-Angle: 14°
h = 2.10 m

Impedance: (30.1 + j 0.2) Ω
Gain: 17.0 dBi
F/B: 24 dB		Invalid shortcode
3dB-Angle: 50°		Invalid shortcode
3dB-Angle: 12°
h = 2.20 m

Impedance: (29.9 - j 0.7) Ω
Gain: 17.2 dBi
F/B: 22 dB		Invalid shortcode
3dB-Angle: 50°		Invalid shortcode
3dB-Angle: 12°
h = 2.30 m

Impedance: (29.5 - j 1.4) Ω
Gain: 17.3 dBi
F/B: 21 dB		Invalid shortcode
3dB-Angle: 50°		Invalid shortcode
3dB-Angle: 12°
h = 2.40 m

Impedance: (29.0 - j 1.9) Ω
Gain: 17.3 dBi
F/B: 20 dB		Invalid shortcode
3dB-Angle: 50°		Invalid shortcode
3dB-Angle: 12°

DK7ZB 5-Element OWM Antenna (l = 1.48 m)

4NEC2 Input:Geometry File
Frequency:144.3 MHz
Stacking DistanceHorizontal PatternVertical Pattern
h = 1.80 m

Impedance: (25.8 + j 0.37) Ω
Gain: 15.9 dBi
F/B: 15 dB		Invalid shortcode
3dB-Angle: 50°		Invalid shortcode
3dB-Angle: 15°
h = 1.90 m

Impedance: (28.2 - j 0.25) Ω
Gain: 16.2 dBi
F/B: 17 dB		Invalid shortcode
3dB-Angle: 52°		Invalid shortcode
3dB-Angle: 14°
h = 2.00 m

Impedance: (28.1 - j 0.8) Ω
Gain: 16.5 dBi
F/B: 18 dB		Invalid shortcode
3dB-Angle: 52°		Invalid shortcode
3dB-Angle: 14°
h = 2.10 m

Impedance: (27.9 - j 1.0) Ω
Gain: 16.6 dBi
F/B: 19 dB		Invalid shortcode
3dB-Angle: 52°		Invalid shortcode
3dB-Angle: 12°
h = 2.20 m

Impedance: (27.8 - j 1.0) Ω
Gain: 16.7 dBi
F/B: 20 dB		Invalid shortcode
3dB-Angle: 52°		Invalid shortcode
3dB-Angle: 12°
h = 2.30 m

Impedance: (27.9 - j 1.1) Ω
Gain: 16.7 dBi
F/B: 20 dB		Invalid shortcode
3dB-Angle: 52°		Invalid shortcode
3dB-Angle: 12°

DK7ZB 6-Element OWM Antenna (l = 2.07 m)

4NEC2 Input:Geometry File
Frequency:144.3 MHz
Stacking DistanceHorizontal PatternVertical Pattern
h = 1.80 m

Impedance: (27.5 - j 3.8) Ω
Gain: 16.5 dBi
F/B: 22 dB		Invalid shortcode
3dB-Angle: 46°		Invalid shortcode
3dB-Angle: 14°
h = 1.90 m

Impedance: (25.7 - j 1.7) Ω
Gain: 16.8 dBi
F/B: 28 dB		Invalid shortcode
3dB-Angle: 46°		Invalid shortcode
3dB-Angle: 14°
h = 2.00 m

Impedance: (25.9 - j 0.2) Ω
Gain: 17.1 dBi
F/B: 33 dB		Invalid shortcode
3dB-Angle: 46°		Invalid shortcode
3dB-Angle: 14°
h = 2.10 m

Impedance: (26.3 + j 0.6) Ω
Gain: 17.3 dBi
F/B: 34 dB		Invalid shortcode
3dB-Angle: 48°		Invalid shortcode
3dB-Angle: 12°
h = 2.20 m

Impedance: (26.7 + j 1.0) Ω
Gain: 17.5 dBi
F/B: 33 dB		Invalid shortcode
3dB-Angle: 48°		Invalid shortcode
3dB-Angle: 12°
h = 2.30 m

Impedance: (27.1 + j 1.3) Ω
Gain: 17.6 dBi
F/B: 33 dB		Invalid shortcode
3dB-Angle: 48°		Invalid shortcode
3dB-Angle: 12°
h = 2.40 m

Impedance: (27.6 + j 1.3) Ω
Gain: 17.7 dBi
F/B: 33 dB		Invalid shortcode
3dB-Angle: 48°		Invalid shortcode
3dB-Angle: 12°

Discussion

Horizontal Distribution

Full Group Survey

Conclusion

Antenna used has been developed by Martin, DK7ZB. Construction data received by private communication.

Description

Results

  • clean horizontal radiation pattern, good side lobe suppression
  • excellent F/B value

 





	Total GainHorizontalVertical






	Invalid shortcodeInvalid shortcode




	Gain [dBi]11.5




	 F/B [dB]37.7




	3dB Angle [°]4838

2x Vertically Stacked

Description

Results

  • horizontal radiation pattern un-affected
  • gain increases by about 3 dB as theoretically predicted
  • F/B value decreases slightly
  • proposed stacking distance: 2.20 … 2.30 m
HorizontalVertical
h = 1.9 mInvalid shortcodeInvalid shortcode
Gain: 14.1 dBiF/B: 46 dB
h = 2.0 mInvalid shortcodeInvalid shortcode
Gain: 14.3 dBiF/B: 40 dB
h = 2.1 mInvalid shortcodeInvalid shortcode
Gain: 14.4 dBiF/B: 38 dB
h = 2.2 mInvalid shortcodeInvalid shortcode
Gain: 14.5 dBiF/B: 36 dB
h = 2.3 mInvalid shortcodeInvalid shortcode
Gain: 14.5 dBiF/B: 35 dB

4x Vertically Stacked

Description

Results

  • horizontal radiation pattern un-affected
  • gain increases by about 6 dB as theoretically predicted
  • F/B value decreases slightly
  • proposed stacking distance: 2.10 … 2.20 m
HorizontalVertical
h = 1.9 mInvalid shortcodeInvalid shortcode
Gain: 16.8 dBiF/B: 28 dB
h = 2.0 mInvalid shortcodeInvalid shortcode
Gain: 17.1 dBiF/B: 3 dB
h = 2.1 mInvalid shortcodeInvalid shortcode
Gain: 17.3 dBiF/B: 34 dB
h = 2.2 mInvalid shortcodeInvalid shortcode
Gain: 17.5 dBiF/B: 33 dB
h = 2.3 mInvalid shortcodeInvalid shortcode
Gain: 17.6 dBiF/B: 33 dB

6x Vertically Stacked

Description

Results

  • horizontal radiation pattern un-affected
  • gain increases by about 8 dB as theoretically predicted
  • F/B value decreases slightly
  • proposed stacking distance: 2.20 … 2.30 m
HorizontalVertical
h = 1.9 mInvalid shortcodeInvalid shortcode
Gain: 18.3 dBiF/B: 20 dB
h = 2.0 mInvalid shortcodeInvalid shortcode
Gain: 18.8 dBiF/B: 26 dB
h = 2.1 mInvalid shortcodeInvalid shortcode
Gain: 19.1 dBiF/B: 30 dB
h = 2.2 mInvalid shortcodeInvalid shortcode
Gain: 19.3 dBiF/B: 32 dB
h = 2.3 mInvalid shortcodeInvalid shortcode
Gain: 19.4 dBiF/B: 32 dB
h = 2.4 mInvalid shortcodeInvalid shortcode
Gain: 19.4 dBiF/B: 32 dB

2x Horizontally Distributed

Description

Results

  • antennas act – almost – independently, checked also by several radii
  • gain drops by roughly 3 dB for 2 antennas as theoretically predicted
HorizontalVertical
r = 1.0 m, φ = 90°Invalid shortcodeInvalid shortcode
Gain: 8.5 dBi
r = 1.0 m, φ = 180°Invalid shortcodeInvalid shortcode
Gain: 8.6 dBi

4x Horizontally Distributed

Description

Results

  • antennas act – almost – independently, checked also by several radii
  • gain drops by roughly 6 dB for 4 antennas as theoretically predicted
HorizontalVertical
r = 1.0 m, φ = 90°Invalid shortcodeInvalid shortcode
Gain: 5.5 dBi

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