The BVO2-2wl yagi by DJ9BV

After moving to south Germany in the end of 1999 I started working with a small 4ele F9FT yagi by Tonna. I installed the antenna on the roof and did some first contacts on 144 MHz. Of course I knew that this wouldn't be satisfied. In summer of the year 2000 I started to replace the 4ele yagi. But first I had to install a small tower system under the roof of our house. Well, I used some small tubes, but it worked fine. After this was done, I could replace the 4ele by my old homemade 9ele yagi designed by Tonna. I realized that this was a big improvement! The antenna wasn't bad, but as you might know, Tonna is not like "state of the art" anymore. After searching a long time for good designs I found the BVO series by DJ9BV published in 'DUBUS Technik V' in 1998. These antennas are the most recent result of a long history of antenna design. They are used across europe by many hams with good results. Due to some power lines across the roof of our house, I'm limited to a maximum boom of 2wl. I started meassuring, calculating and thinking how to get the maximum of my limited space. In the end, my decision was to build a stacked 2 x 2wl BVO antenna system by DJ9BV.

During the time of searching and developing I found some very interesting internet pages. Check them out:


Based on these informations, I started building my own 2wl BVO antenna system.

BVO2-2wl mechanical construction
Due there are several detailed descriptions of building this antenna type, I notice only some interesting and important points here. For more detailed infos about the mechanical construction of DJ9BV yagis, I recommend the pages I mentioned before.

Elements
The original antenna datas using solid 5mm aluminium rods for the parasitaric elements. For this diameter I couldn't find any element holders. But Claus, DF8GH, asked the designer DJ9BV for recalculating the antenna using 4mm elements. This allows to use the well proved method with the nylon rivets used already in the former BV yagi series with great succes. The elements were hold in place by two rivets, so the aluminium rods are mounted isolated through the boom. A method that provides long term good and reliable results, is well and often tested and is a quite simple method for fixing the elements.

Driven element
Due to the near 50 Ohm intinsic impedance the realization of the driven element can be done in differrent ways. The designer DJ9BV recommends the classic folded dipole with a 4:1 transformation as a mechanically and electrically reliable solution. This has be done very successful also in the former BV-yagi series. Although there could be some matching difficulties in highly optimized/frequency range limited yagis (like the BVO series). The near 50 Ohm impedance allows also another more simple style of DE:
As pointed out in the DUBUS magazine 4/98 by Graham, F/G8MBI you could also use a simple straight split dipole and connect the feeding line direct to the antenna. This solution has several advantages:

  • no additional losses in a transforming balun
  • no less garantee for a balanced, straight pointing antenna (unequal current distribution also possible with a folded)
  • no interaction of the balun in the yagi structure and the elements
  • less weight, wind load and mechanical complexity
  • less difficulties in achiving a good match in 'narrow banded' (=highly optimized) designs

I chose to use the simple straight dipole. The two legs of the dipole are fixed isolated on the boom with a gap of 10 mm. There you can directly connect your feeding line and run it on the boom towards the pole where it can go down without influence the antenna. I used some plexi tubes to adjust the two legs and keep them straight.

Boom material and support
I chose a square aluminium tube 20 x 20 x 2 mm. It is a good compromise in terms of stability and weight. To hold the antennas in place I used a cord support. This is a very simple and weight less solution.

Element boom correction
For different boom diameters you have to add the following amount to the free space length:

  • 20 mm + 2 mm
  • 25 mm + 3 mm
  • 30 mm + 5 mm
  • 35 mm + 6 mm
  • 40 mm + 8 mm

The mechanical datas of BVO2-2wl (4mm parasitic elements and 8mm driven element):

  position [mm] length free space [mm] length 20mm boom [mm]

R

0

1014

1016

DE

327

958 (8mm tube !)

958 (8mm tube !)

D1

534

952

954

D2

1073

938

940

D3

1828

921

923

D4

2687

912

914

D5

3540

907

909

D6

4245

918

920

Electrical datas by means of NEC II (DJ9BV)

  • very low internal losses (< 0,1 db/6K)
  • 45 - 55 Ohm input impedance (180 - 220 folded dipole)
  • F/R (90° - 270°) > 23 db
  • Gain: 12,1 dBD
  • E-Aperture: 35,4°, H-Aperture: 38,8°
  • E stacking distance: 3,36 m, H stacking distance: 3,16 m
  • stack gain: 5,97 db

Graphics
Mechanical construction data Horizontal diagram - calculated with AO 6.59 de K6STI Vertical diagram - calculated with AO 6.59 de K6STI Meassured horizontal diagram of 2x2wl system

Conclusion
I finally installed my 2 x 2wl BVO antenna system with a stacking distance of 3.16m in August 2001. The gain should be at least around 14.5dbD. I realized a good improvement to my old 9ele F9FT. I use a homemade antenna coupler designed by DK7ZB (refer to 'project' section). I also installed a new pneumatic telescopic tower system by "BigLift". This gives me the posibility to move the antennas some meters up, which is strongly recommended at my location.

Special thanks must go to my dad, DJ9CZ (SK), who helped me setting up the new system!

Update 06 Feb 2004:
After more than two and a half years of use, I'm still very satisfied with the system. It survived several storms without a damage. During very foggy weather conditions sometimes the SWR gets slighty up. But I think thats the price you have to pay for a highly optimized system. Until now I achieved two EME qso's with this system and a total of #217 squares. For the future I would like to upgrade to a 4 x 2wl system... or maybe 2 x 3wl... :-)

Update 17 Sept 2004:
Finally I put down the 2 x 2wl system during August 2004. Although the system was working very fine, I chose to setup a new system with 4 x 7ele, in order to get the possibility to elevate the antennas. So far I have only a single 7ele running for some tests, which is working pretty good. The plan is to raise the new system during spring / summer of 2005.