Small EME yagi antenna system for 144MHz - design by DD0VF

Introduction:
For several years I have been running a 2 x 8ele yagi antenna system with an optimized design by DJ9BV. The stacking distance was about 3.0m in the H-plane. This system worked pretty good. After a while, I realized the necessity to get some elevation possibility to the system. Due to mechanical reasons, it is very difficult to get a 2 x H-antenna system with elevation. So, I needed to stack the system in the E-plane. But, because of the very limited space on the roof of our house and due to some close power lines, the 4.25m of the boom and the approximately 3m stacking distance of the 8ele was too much.

I searched the internet for a good and compact yagi system. I found the 4 x 7ele antenna system done by Steffen, DD0VF. He has realized a very compact system. Due to TVI reasons the system is optimized for reduced sidelobes. This leads to a very short stacking distance, but remains still enough gain for working EME. Please check Steffens webside for more details of his system.

The original calculations by Steffen have been done using "YO - Yagi Optimizer" by Brian Beezley, K6STI.
I recalculated these data using the "Yagi Analysis V3.54" by Goran Stenberg, SM2IEV and "YA - Yagi Analyzer" by Brian Beezley, K6STI. YA is a reduced version of the "Yagi Optimizer" and calibrated to NEC, the high-accuracy Numerical Electromagnetics Code from the Lawrence Livermore National Laboratory. My re-calculated data may not be as correct as the original data of Steffen, but for practical use the accuracy should be high enough.


Calculated electrical data:

 

1 x 7ele

2 x 7ele,
2.0m in E-plane

4 x 7ele,
2.0m in E + H-plane

Gain [dbD]

> 10.5

> 13.2

> 16.1

F/R [dB]

> 27

> 29

> 31

Impedance [ohm]

20.0 -j0.3

20.2 +j0.3

20.4 +j0.9

-3 dB point E [°]

43.2

25.6

25.6

-3 dB point H [°]

50.1

50.1

28.9

Forward Temp [K]

175.4

189.3

193.2

Sidelobe Temp [K]

71.8

30.2

18.8

Backward Temp [K]

3.1

2.7

2.5

Loss Temp [K]

3.2

3.2

3.1

Total Noise Temp [K]

253.5

225.5

217.6

G/T [dB]

-11,32

- 7,69

- 5,08

Frequency: 144.200 MHz
Temperatures used: Tsky=200K, Tearth=1000K

Mechanical data:

 

Element position
[mm]

Element length
(free space) [mm]

Element diameter
[mm]

R

0

1020 **

10

DE

262 *

970

12 (F9FT Dipole)

D1

545

945

10

D2

1027

919

10

D3

1664

898

10

D4

2413

871

10

D5

3150

828

10

* The dipole position is slightly different of the original DD0VF design. I optimized the position, in order to get the best possible SWR on the antenna. The original position is 272mm.

** I did some experiments with the reflector element. Right now, I'm using a slightly longer reflector. This leads to a better SWR in the range of 144.000 to 144.600. But I'll do some more tests. This change should only have minor effect on the antenna performance.


The 10 x 1 mm aluminium tube elements are fixed on the boom using the bottom part of the "Konni" element clamps. These clamps are cheap, easy to fix and very reliable. Like Steffen, I'm using the original F9FT Dipoles, which have a 12 mm diameter. The boom is a 20 x 20 x 1,5 mm aluminium tube.

I chose a stacking distance of 2m in E-plane. This seems to be a good compromise between gain and reduced sidelobes. It also reduces the maximum operation radius of my antenna system to approximately 2m, which is neccesary due to the limited space on our roof.

Steffen recommends a stacking distance of 1.95m in E-plane and 1.77m in H-plane. This leads to some less gain but more reduced sidelobes, which can be more important if you have some TVI problems.

Technical data:
Please check out some technical construction details and screen dumps of the calculation program.

Calculated data, single 7ele, overview Calculated data, single 7ele, graph Calculated data, single 7ele, plot E-plane Calculated data, single 7ele, plot H-plane
Calculated data, 2 x 7ele, plot E-plane Calculated data, 2 x 7ele, plot H-plane Calculated data, 4 x 7ele, plot E-plane Calculated data, 4 x 7ele, plot H-plane
Calculated Noise / Temp data, single 7ele Calculated Noise / Temp data, 2 x 7ele, 2m in E-plane Calculated Noise / Temp data, 4 x 7ele, 2m in E + H-plane
Construction drawing, single 7ele

Project Links:


Many thanks to:

  • Steffen, DD0VF, for the good and reliable data of the 7ele antenna.
  • My dad, DJ9CZ (SK), without its help i wouldn't have get the system up to the roof.

Project status:
In the beginning of the project I planned to set up the 4 x 7ele system. But so far, I only realized 2 x 7ele system, stacked in E-plane, which I have in use since 05/2005.