My antennas started out life as Moonraker 2, 4 & 6 metre Yagis. These were bought for convenience when I initially set up at this QTH; the previous antennas were at the end of their useful life. I had a Moonraker 5 element 6m and a 5 element 4m and an 11 element 2m. I also came by some more 25mm square section (box) aluminium leftovers from a friend's antenna build. The elements are 1/2" and 3/8" so one section slides inside the other nicely. Pop's original design has variations for several element diameters but the elements do not taper like mine, this needs additional calculation (kindly done for me by Pop).

The question which comes up most often is "Where did those element mounting brackets come from?"

Again these are 'left-overs' from the Moonrakers. Pictured (right) is a close-up of one the brackets mounted normally on the boom but without the element inserted. The original design is such that a stainless steel bolt travels through the centre of the element bracket, through a hole drilled in the element itself and is fastened by a nut on the underside of the boom. What is clear from this design that little or no consideration is given to the electrical characteristics of this method of fastening the elements to the boom.

All Yagi designs require a set of criteria in order to optimise the design. Not only do the element lengths and spacings matter, but the type of matching, type and size of boom, whether the elements are mounted through the boom or above/below it, whether the elements are electrically insulated from the boom or otherwise. Pop's designs are calculated for insulated elements, mounted above/below the boom. YU7EF's website has a boom correction diagram which can be used to amend the element lengths according to the distance from the centre of the boom (in boom diameters) to the centre of the element mounting position. This is very important for the finished product to demonstrate the intended design characteristics!

Back to the issue of insulation. As I mentioned previously, the original Moonraker antennas appear not to take account of element insulation. In the Moonraker's original form, it is possible for the element to be twisted slightly and make electrical contact with the bolt (pictured) which itself is in electrical and mechanical contact with the metallic boom thereby altering the characteristics of the Yagi. To ensure full compliance with Pop's original calculations, I drilled out another 0.5mm in the element itself and placed two layers of heat-shrink-sleeving over the section of bolt which passed through the hole drilled in the element. This then provides the electrical insulation necessary to comply with the design, while maintaining good mechanical strength. It just so happens that the insulated brackets supplied with the Moonraker antennas place the elements in EXACTLY the correct position (boom diameters) when they are fixed to a 25mm square section boom! Needless to say as soon as I discovered this, I was not going to be making brackets any more!

One point I would like to make at this stage is the positioning of the elements on the boom. Pop's designs (and all Yagi designs) are BEST WITH THE ELEMENTS MOUNTED BENEATH THE BOOM, not above them; this makes for a much more physically balanced antenna than having the elements mounted on the top and should be considered BEST PRACTICE. In my construction, I used the brackets left over from a previous commercial antenna, these plastic brackets are, like many plastic products, moulded and have various internal strengthening support struts and cavities. The cavities would be prone to filling with water in rain storms and would unnecessarily add to the weight of the antenna and is the ONLY reason I did not mount the elements beneath the boom, much as I wanted to.

An EXCELLENT example of a YU7EF build is one completed by Alain, ON4KST 10 element behemoth! Further information about my experience with YU7EF antennas and be found by navigating back to my home page and following the menu G7CNF Stuff > Radios & Antennas >

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