Thursday, June 23, 2011

Review of the OptiBeam OBW 10-5 a ten element wire yagi for the HF bands

‘Efficient, light weight and low visual impact’ the OptiBeam OBW 10-5

Review of the OptiBeam OBW 10-5 a ten element wire yagi for the HF bands

Antenna description

The OptiBeam OBW 10-5 is a very compact five band wire yagi covering 14, 18, 21, 24 and 28 MHz amateur bands (Figure 1 and 4.). There are two elements on each band. The 4 largest elements, those for 14 and 18 MHz are so called Moxon rectangles. This design was derived by Les Moxon (G6XN)[1], from earlier work by VK2ABQ[2], as a way of reducing antenna size with little if any compromise in performance. Typically a Moxon antenna will be around 70% of the element length of a conventional yagiand have a slightly shorter boom. OptiBeam have taken this thinking much further with their computer aided design approach and seem to have solved many of the problems with multibanding Moxon elements.

The main structural component of the antenna is a 5 element driver cell using a rigid phasing line which results in a very close match to 50 ohms over all of the HF bands. A 1:1 balun capable of passing 3 kW is available too.

A special feature of this antenna is that 9 out 10 of its elements are stainless steel wire, very strong and flexible. This innovation dramatically reduces weight, wind load and most importantly these days, the visual impact of the antenna. The use of stainless steel elements may raise some eyebrows as stainless has much higher bulk resistivity than aluminium but in fact losses caused by this are very small, maybe a fraction of a dB, according to modelling with EZNEC.


The antenna consists of a frame made up from the boom, half of which is the phasing line, and the 28MHz element. This is extended with 4 fibre glass extensions as a pair of Vees. The figure shows this easier than I can describe.

The wire elements are attached with non conducting blocks to the frame. The elements are tensioned using elastic cables and by stretching the frame itself. Most cable to element connections use an insulator and a stainless steel shackle – very neat.

The antenna is shipped in a large box and is supplied part assembled.

This makes life a lot easier and OptiBeam claim that it can be assembled in 1-1.5 hours – well I guess if you are assembling one every day maybe, but it took me about 3 hours. All components are made to the usual high OptiBeam standard so they fit very accurately together. The instructions are comprehensive and well illustrated but are written in a strange style, OptiBeam say they will clarify some of the more obscure passages in the next brochure release. All the nuts and bolts are stainless, and the nuts are self-locking. As usual, OptiBeam supply a small set of tools, a tube spanner and Allen keys, which facilitate assembly, and a few spare nuts and bolts, just in case!

I assembled the complete antenna on the ground. I had one incorrect element but this was quickly replaced by OptiBeam. All of the various sub-components are very clearly marked and fitted exactly as described in the manual. Some care in assembly is necessary so that the elements are evenly tensioned. A truss is used to ensure that the antenna does not ‘flop’ down when it is on the tower. This means that there must be about a 1.5M stub mast above the antenna.

Although this antenna can be assembled by one person the final tensioning of the assembled frame and elements is much easier if two people can each pull from either end and tighten up the frame when the elements are taut.

Getting it on your tower or mast.

At 14 kG this antenna is reasonably light compared with many all aluminium yagis. You can easily pick it up in one hand. Although the instructions describe how to mount the antenna onto a mast, OptiBeam show a mast with a hinged rotator so that when the tower is luffed over, the stub mast remains vertical. Most of us don’t have such a facility on our tower and when luffed our stub mast is horizontal or even inclined. As this antenna has closed element ends, (the bent-in ends of the Moxon elements), it has to be lifted over the stub mast because it can’t be fed in from the side as one can do with a normal yagi. This isn’t a problem in itself, I mention it only to highlight the necessity for a bit of forethought. Again a second pair of hands come in useful, but I managed by myself. The light weight is a major help.

I had thought that tensioning the truss would be a bit difficult but using the OptiBeam dimensions it was correct first time and when the tower was vertical, the antenna looked slightly upward bowed, just perfect.

First impressions

When the OBW 10-5 was up in the air I was immediately stuck by how small and compact it looked. It is LOT less visible from a distance. Even my wife commented that it looked much less visible than my normal antenna.

It is also light and well balanced, so a small rotator would handle it easily and no worries about wind resistance either. It sailed through the storms at the end of November 2006 without any problem.

But how does it perform?

On all bands the antenna behaves as a two element yagi. On 24 and 28 there is claimed to be some extra gain from interaction with unused elements. I have no way of measuring forward gain but a series of measurements of front to back ratio under various conditions showed that it was very close to claimed specification (Table 1.) and under some conditions exceeded them.

The practical SWR measurements (antenna at 18M, 20M feeder) were substantially to specification as well and the antenna permitted my transceiver to generate full power over all bands covered (Table 1.).

Table 2. SWR measurements


Band edge SWR

Lower Upper


1.2 1.3


1.2 1.1


<1.1 1.3


1.3 1.1


1.1 1.5

I have used this antenna to crack a few DXpedition pile ups and its performance was as expected. Yes, I know that this is hardly an objective test – but anyone who has waited in line will know exactly what I mean. Plenty of W6s were worked on 20m in CQWW CW.

Looking at the performance differences between various antenna designs shows that the OBW 10-5 gives up less than a dB to a beam with conventional elements like the OptiBeam OB 9-5 which weighs in at 25kg and has a boom length of 5.1M against the OBW 10-5 of 3.7M! Indeed the OBW10-5 is only about a dB below the gain often quoted for a typical 3 element yagi! Of course with a light weight antenna one can often mount it higher than a heavier one and thus exploit height gain for even better performance, and be able to leave it up during the winter gales!

From size and weight aspects the OBW 10-5 should also be considered for DXpedition use. Although the longest components (the fibreglass rods) are a bit long for the average ski bag, with some judicious disassembly and packing it might be possible to make them fit.


The OBW 10-5 seems to me to be an excellent antenna. Frankly its performance is very good for its size. It should easily outperform many so-called miniature beams especially if they use lumped loading devices or traps. The OBW 10-5 should be considered by anyone who needs a low visual impact antenna, which at the same time is light weight and well constructed. It should last for years.

Further thoughts.

To evaluate the OBW 10-5, I had to get my own OptiBeam off my tower. This enabled me to give it a close inspection for corrosion and wear. It was in near perfect condition, a tribute to the designed-in quality of OptiBeam products.

Finally if you want to read more about the Moxon antenna one of the best websites is, that of L.B.Cebik, W4RNL[3].

The views in this review are those of the author and do not imply any liability or warranty with regard to this product either direct or arising from any comments made here.

Price and delivery

OptiBeam products are available in the UK from Vine Communications or direct from Optibeam. Check the OptiBeam website for latest pricing. Many thanks to OptiBeam for the supply of this antenna for evaluation.





  1. L.A Moxon G6XN, HF Antennas for all locations, pg. 168 – 176, RSGB. (RSGB Bookshop)
  2. F. Caton VK2ABQ.G3ONC Electronics Australia, October 1973.

3. Cebik Antenna pages and also ARRL Antenna Compendium, V6, pg.10.

Table 1. Specifications

Bands covered

20 / 17 / 15 / 12 / 10

Gain (dBd)

4,2 / 4,4 / 4,2 / 4,4 / 4,8

Front to back ratio (dB)

21 / 17 / 15 / 15 / 20

SWR: 14,00 - 14,13 14,35

18,07 - 18,14 - 18,17

21,00 - 21,25 - 21,45

24,89 - 24,94 - 24,99

28,00 - 28,50 - 29,00

1,8 - 1,3 - 1,8

1,5 - 1,4 - 1,5

1,5 - 1,1 - 1,5

1,4 - 1,3 - 1,4

1,5 - 1,2 - 1,6


10 ( 9 wire elements)

Active elements per band

2 / 2 / 2 / 2+ / 2+

Longest element (m)


Boom length (m)


Turning radius (m)



1 Coax 50 Ohm

Weight (kg)


Wind load at 130 km/h

242 N / 0,30 m² / 3,2 feet²

List price


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