Dx Adventure Radio Club (DA-RC) member PD5MVH Marcel (19DA109) is looking forward to testing a monster new OB7-3 antenna at his home station in the Netherlands in the coming days after some positive experiences in a recent field day event led him to purchasing one.

A gigantic 7 element yagi which covers 3 bands (20m, 15m and 10m) and one which provides outstanding gain and front to back performance, this antenna is manufactured by German company ‘Optibeam Antennas’ and is regarded as one of the best triband antennas of its type available in the ham community.

As most DA-RC members will know, Marcel currently uses the PKW 3 band antenna and while he finds monoband performance okay, the multiband performance has been not as good.

“Hopefully the OB7-3 will arrive next week and so I can fix to lagers in the top (GS065) and the new rotor G-1000,” explains DA-RC’s well known dx adventurer.  “This one you can use also in other bands little tuning but so what some power lost.”

Below is some nice information provided by Marcel about his new antenna purchase…

OB7-3 Infos

The boom is square and consists of two sections, coupled by special designed coupler latches.

It is a 40x40x2.0mm boom which makes the assembly of the 7 elements a snap; all is in line from the first moment on.

The elements are installed on element platforms which have to be installed below the boom by corresponding square brackets, so an absolutely easy installation procedure.

The elements are heavy duty designs, tapered many times:

-> 20m: from 30×2.0 to 12×1.5

-> 15m: from 20×1.5 to 12×1.5

-> 10m: from 16×1.5 to 12×1.5

Each element position is marked on the boom by two lines, and the element platform has just to be put in between these lines and fastened.

The coupling of the element segments is realized by a special screw technique which we have designed and which makes the coupling super easy and quick, and no measuring is required at all, all pre drilled, just pushing one section into the previous one and that’s it.

The three driven elements are connected by two square tubes which run along them in parallel arrangement; we call it “square tube phasing line”.

This driver cell is wider spaced, there is a distance of 50 cm between each of the driven elements, and in combination with the square tube phasing line it results in a broad band high Q feed system, so perfect SWR is achieved and the energy transportation from the driver cell into the parasitic elements is loss free.

Electrically the OB7-3 works as follows:

-> 2el full sized monobander on 20m

-> 2el full sized monobander on 15m

-> 3el full sized monobander on 10m

We do a lot of analyzing on the computer and do a lot of practice measurements.

Just for comparison, a trapped 3el tribander has a gain of about 3.5 dbd (gain over dipole in free space) as an average on all three bands, as long as the traps are new and of high quality (90% are not!).

And the older they become the more they lose efficiency.

Furthermore, trapped Yagis have a rather steep vertical takeoff angle due to the destroyed current distribution on the elements and the smaller antenna surface.

As another comparison, log periodics usually have a pretty small active region on each band and the elements are driven 180 degrees out of phase.

Therefore the gain is limited, even on bigger log periodics, and the take off is pretty steep as well.

The OB7-3 has about 4.2 dbd on 20m, about 4.3 dbd on 15m and about 5.5 dBd on 10m. 

It also has clean patterns and very good SWR.

Theoretically it has just 2 active elements on 20 and 15m, but due to the multi element structure and the positive interaction of the 10m director into 15m and the 15m driver into the 20m band some additional performance is developed.

Also find attached some pictures of installed OB7-3s.

And please have a look on our web site www.optibeam.de under antenna parts; you will see all the things which I have explained above.