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After much research I decided to build a fairly small Yagi antenna. At first I had toyed with the idea of using a 3 element quad antenna but after looking at the complexity of build decided to attempt a 'plumbers delight' beam to allow quick operation and therefore test to see if the band was worth further exploration.
I decided to build an antenna that had the following qualities:
I have 10 watts of RF available therefore maximum gain is important.
The antenna would need to be quick to construct and set-up.
Good front to back would be important.
The beam had to be cheap to make.
It had to be light and easy to use
I found that there was plenty of information about 6m antennas available but little for 4m and therefore I had to develop the beam from scratch. After calculating out the beam dimensions several times I found a balance that, in theory, would have 8.3dbi gain with a front to back in the region of 28db with few side lobes whilst still only having 3 elements.
I had set a maximum boom length of 1.7 metres because that was the length of a boom section that I had available. I discovered that the main problem with beam construction is element material and element mounting. Many designers seem to complain of the problems when attaching round element stock to boom sections.
Taking this into consideration and by nature being un-conventional I decided to simplify the mounting process by using elements made of 12x12mm angle aluminium 1.5mm thick. This would give the elements strength whilst provide an easy mounting to the 25mm square aluminium boom.
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