OptiBeam OB4030-P Tech Tip

OptiBeam Tech Tip

OptiBeam DBO-OB4030-P

4 Element 2-Band Yagi

This Tech Tip is from Tom, President of OptiBeam Antenna Technologies, call sign DF2BO, known on the air as DF2BlueOcean.

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A customer requested information about the OB4030 Antenna

Regarding the OB4030:. 1 Like all our other antennas the OB4030 is a computer designed antenna, which of course

has also been run through some extensive on the air tests.

2. The OB4030 is a two by two combo, so it has 2 active elements on each of the two bands.

3. The elements are effectively shortened by high Q coils. Both bands use the same coil at the same position within the element, and so the 30m elements are physically shortened more than the 40m ones.

4. The gain on 40m is just about 0.6 dBd below that of the much larger full sized brother. As on 30m we only have to cover a 50 kHz spectrum we have electrically tuned the reflector for a self resonance frequency which is rather close to that of the driven element, and so we could achieve a gain figure which is almost as high as that of a 2 element full sized Yagi.

5. Because shortened elements couple stronger with each other the f/b ratio on both bands is better than that of a full sized Yagi. And on 30m it is extremely high, comparable to that of a well adjusted 3 element Yagi.

6. Interaction to nearby antennas in the frequency range of 14 up to 30 MHZ is totally avoided on both bands by the carefully position of the coil and on 40m in addition by the use of our decoupling stubs. How their function would be too complicated to be explained here, but there function is also proven in practice by many installations. This means, another 2015-10m tri-bander or 20-17-15-12-10m five-bander or several other antennas of this frequency range on the same mast do not suffer from the OB4030 being in the vicinity.

7. Both driven elements are not as close spaced as this would result in a lossy system with limited band width and reduced efficiency. The distance between the drivers is one meter = 3 ¼ feet. The drivers are connected by two parallel square tubes which we call phasing line and which has a wave resistance of about 80 Ohms. This results in a high efficient way of feeding both bands commonly by finally having the feed point at the 30m driver and by using a high quality 1:2 balun.

8. The elements are extremely rugged. In the centre we use a 40 mm diameter. The 30m elements, being rather short with the coil in use, are absolutely stiff and almost horizontal. The 40m elements have an element truss system, consisting of a UV resistant element guy rope and a guy tower in the centre. So the trussed 40m elements also are almost horizontal. This results in a great optical appearance and makes the elements more robust in high winds as the wind surface area is reduced this way.

9. The element transitions are realized by a self developed and absolutely unique screw technique, simple to assemble, rock solid, ever lasting, and always easy to disassemble. And of course we use stainless steel hardware and the nuts are self stopping.

10. The elements are mounted onto 500 mm long extremely robust U-shaped element holders. The element centers are screwed onto the element holders by the use of four UV resistant tube holders (hydraulic clamps) built of synthetic material.

11. The boom consists of three parts and is made from 80x80 mm square tubing. It is very robust. This guarantees that even in highest winds the elements never will get out of their straight line and makes the mounting very easy.

12. The boom to mast plate is a square shaped plate, built of extra hard aluminium. It has a dimension of 300 x 300 mm. In the vertical four stainlesss steel M8 U bolts are inserted into it which embrace the mast. In the horizontal you find four square brackets which are used to mount the plate to the boom.

I hope that the above information helps show you that you would make an excellent choice with the OB4030.

73, OptiBeam Antenna Technologies

President

(Thomas Schmenger), Tom, DF2BlueOcean