I have now had a play with some hombrew verticals with excellent results. I have always fancied trying out a beam just to satisfy my couriosity on how well they perform compared to omni directional. To get my feet wet i thought i would tackle a simple two element beam first and for this i chose a quad rather than a yagi. On this page i will give each step of how i built the quad and all measurements including the materials i used so if you decide to build one it should help take out some of the working out and looking for plans.
The first step was to measure out 90 inches of wire, for this i have some 2.5mm flat grey electrical cable, the type electricians use. Its single stranded coated copper wire. Inside the grey insulation is 3 wires...one red, one black and in between a bare copper earth. Using cutters open the end of the cable exposing the 3 wires then with pliers pull the bare wire and this will cut through the grey insulation leaving you with 3 X 90in lengths of wire. Only keep the red and black wires, with stripping the bare wire out it ends up with lots of kinks in it besides its bare so throw it away.
I nominated the red wire for the driven element but it does not matter its just a colour. This stuff is pretty tuff so grabbing half an inch in a vice makes a good anchor to pull the cable as straight as possible, the measurement is crucial.
Pulling it as straight as possible and measuring it out to a length of 81.5in but i only cut 81in.....Remember theres half an inch in the vice!
So to recap thats the driven elements length @ 81.5in and when made into a square will give each side a length of 20.375in.
Things starting to take shape now, the white piece of anle upvc was some off cuts from the guys who fitted plastic soffats and barge boards. I always hang on to any reseanable lengths of off cuts Plastic pipes, copper pipes, wire you name it anything that looks interesting. I have hung on to that 90 degree plastic for almost 2 years and now i know why. Drilled two holes spaced at 20.375in apart making them as close the corner of the plastic as possible so the element touches the plastic.
Above is the reflecter and the dimesions are: 86 inches (making a square loop that is 21.5 inches per side).Both ends are connected (soldered) together to make a complete electrical loop.
With both the driven and reflecter elements built i attached them to a boom with a length of 15.25ins The boom became a bit of issue as i intented to make the beam easy to take apart and reasemble for use out and about as a portable antenna but it was to flimsy and several screws and tacks later it stays put together but still fits into the boot of the car.
I found the balanced point on the boom then nailed a short piece of timber to the boom (i used nails because i run out of screws) and hooked up the coax to the driven element in a vertical polarized way as im only using FM but it could easily be changed to horizontal polarizitation by turnig the whole of the beam 90 degrees.In the vertical polarization the inner core of the coax goes to the top (upper) part of the element and the shield to lower part or the wire that goes down. I should really have taken a pic of this...oooops! Around the boom i wound 7 turns of the coax to make a choke to help prevent RF going back down to the radio.
I was running out of time and due to go to work in couple of hours but getting this far i had to get the beam on air just to see if it actually works. One PL259 and my Kenwood H/H set @ .5w output i checked the SWR. Hmmmm 2 to 2.5.:1 across the 2 meter band but out of the red. Looks like the driven element needs shortening a little none the less as i swung it round it indeed was a beam and very directional. I had to try it and got into the local repeater with ease and fully quitening on half a watt with the beam only 4 ft of the ground. A little trimming of the driven element and this is going up in the near by hills soon and ready for summer 2004. Its not designed to stay outdoors in all weathers just my answer to the SOTA beam.....73s