Well it looks like the sunspot cylce is on the rise again and that means BIG DX!!The beam below is very simple to build as well as light weight. Gain on this 4 element beam is about 9 or 10 db.
The boom is made from 2 ten foot sections of TV masting. You will need 4 lenghts of 1 inch tubing and 4 lenghts of 7/8 inch tubing. Both of the tubings should be about 10-12 feet long.I've found that the best way to mount the elements to the boom are with regular 2 inch automotive muffler clamps. You will need to purchase some 1 inch aluminum angle iron from a hardware store, about 4 feet. Cut this angle iron into four 12 inch sections. It will be used to support the element to the muffler claps to the boom.
Ok we will start by finding the center of the 1" elements. Mark the tubing. Now measure 4 inches out from that mark on the tubing and make another mark. Do the same thing going the other way from the centerof the tubing. Now drill a 1/4 hole threw the element at the marks you just made. Do this procedure to all 4 of the elements. At the end of the elements you will need to make slit about 2 inches long. Use a hacksaw and go very SLOW making shure that the slit is in the center of the tubing while cutting at all times.
* figure a *
O.K>??....Good. We will now start on the angle iron brackets. Start by finding the center of the 12 inch bracket. Make a scratch mark on the bracket in the center. Now measure 4 inches out from that center spot on the bracket and make a mark. Do the same thing going the other way from the center scratch. You can now drill a 1/4 inch hole threw the element at the marks you just made. Do this procedure to all 4 of the brackets.
Still with me??..Good. You should have 4 brackets with one side of the bracket having 2 holes that are 8 inches apart from each other. That is the side that will be mounted to the elements of the antenna. So lets go back to the center scratch on the bracket and on the other flat side and measure out 1 inch away from the scratch and drill a hole. The size of the hole will differ depending on the thickness of the muffler clamps. Do this to all 4 of the brackets.You assemble the antenna elements to the bracket by putting the element along the outside of the bracket and put a inch and 1/2 inch 1/4 inch bolt threw the 2 holes. Make sure to put a washer and lock washer on the bolt. This will reduce the chance of the antenna falling apart ,when its up in the air, and aslo not crushing the nut into the element. A good idea is to later put some silicone chaulking over the threads of the bolt after you tighten it up. Assemble all the brackets like this.
Figure b shows the arrangement of the elements on the boom as well as the spacing of them. So slide the brackets on the boom .Put the first one at the end of the boom/TV masting and tighten it up. Then the next one is six feet down the boom , then 5 feet , then 8 feet. You will notice that the last element is almost at the other end of the boom. You can cut off the extra foot if you wish.
Now that the elements are all spaced out on the boom its time to build the elements themselves. You do this by cutting the four 7/8 inch thick elements in half. So that you have 8 5 foot rods now. Slide a rod into the end of each element and adjust them untill you have the specified legnths (see figure b for the size of the reflector ,driven element, and directors) . Once you have the elements all sized up you can slide on a 1 inch HEAVY DUTY hose clamp and screw it tight.
* figure b *
O.K. Now here comes the tricky part .The gamma match. Your going to need to get a piece of 3/8 inch tubing about 24 inches long. Also cut yourself a 25 inches of RG-8 coax ,use the stuff with the foam inside i like it better then that plastic stuff they use in some cable. Strip off the black outside jacket and remove the copper braid so that you are now left with just the foam and the center wire. Then cut off just 1 inch of the foam. Slide the conductor into the 3/8 tubing and thats it you have a gamma match! (see figure c)
* figure c *
Next thing to do it to build a bracket for the gamma match. You will need some aluminum sheet metal. Cut the metal to 4 inches wide by 3 inches tall. Put a 90 degree bend in the metal so that there is a 1" x 4" area and a 2" by 4 inch area. Now on the 2 by 4 inch area find the exact center and put a mark there by tapping the point of a phillips head screwdriver so that you have a small dent there. Cut a hole there so that you can mount a SO-239 chassis mount connector. On the 1" by 4' area find the center and drill 2 holes 1 inch away like you did to the bracket above. Mount this bracket to the muffler clamps on top of the driven element bracket.(see figure d)
* figure d *
Now you will need to get some more sheet metal to build the SHORTENING strap of the gamma. This may vary in size depending on the space from driven to the gamma match. The gamma match is mounted along the side of the driven after you have soldered the innner conductor of the gamma match to the center of the SO-239. The spacing is usally about 1.5 to 2 inches from the driven element (Dosen't make much difference). To make the SHORTENING strap cut a 1 inch strip about 6 inches long. Take this strip and bend it around the driven and over to the gamma. Make sure it folds back over so that you can drill 1 hole at each of the ends of the strap. Drill the hole threw the strap and put a small bolt and nut in it.
Now that you have the beam all assembled its time to tune the antenna. You can stand the the antenna so that it is pointing straight up. Lean it up againt a six foot folding ladder for support. Hook up some coax to your radio and put an SWR meter just before the antenna. Key the radio on AM with no audio and take a reading. If the reading is high then loosen the shorting strap and move it up or down the gamma rod and driven element until you get a good reading. Once you get a good reading then tighten the 2 small screws on the strap and put the antenna up on your mast.
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