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location: A2m-70cmdipoleantennafor6bucks

My radio pretty much busted the budget and even though it covers 2m and 70cm bands, I didn't have an antenna for those bands. I built this dipole for $6 and it covers both bands with a SWR of less than 1.2:1 across both bands.

I started with the following:

Start by drilling two 3/32" holes through the dowel that are 1-3/4" apart and near the mid-dle of the dowel.

Next, cut 2 pieces of copper wire that are 26" long. These will become the radiators. The starting measurement for the 2m radiator is 18.5" and the starting point for the 70cm radiator is 6.5".

Strip the jacket 2" from the end of the coax cable and pull back the shield. Twist the shield and tin it with a soldering iron. Next, strip the core leaving about 3/4" of it insulated and tin the core.

Bend the copper wires 90 degrees 7" from the end and thread the short end through the holes you drilled through the dowel. Next bend the short end of the wire so it now forms a u and runs down both sides of the dowel. Do this for both peices of copper . The short ends of the wire should be on one side of the dowel and the long ends should be on the other side.

Solder the core to one wire as close to where it goes through the dowel as possible and do the same with the shield on the other wire.

Pull the opposite end of the coax through the tee and feed the dowel through the tee so it looks like the picture below.

IMG_20120930_180331.jpg

Obviously, I've added tape to the dowel to hold the elements in place. That's because sharing this design was an afterthought and i didn't have a photo showing the correct amount of progress. Go ahead and tape the elements in place but leave the last couple of inches of each element free so that you can trim them to tune the antenna.

Adding the pvc cover will electrically lengthen the antenna so we will need to tune the antenna. Do that by installing (without gluing) the 1/2" pvc pipe covers and measuring the SWR for the antenna. You'll want to start with the 70cm band. I've purposely made them too long and shortening them will lower the SWR. Remove 1/8" from each element and measure the SWR until the swr begins to go up. when it starts to go up you've finished tuning the 70cm elements. Remember, you must shorten the element and replace the pvc cover before remeasuring the SWR.

When you are done with the 70cm elements, repeat the procedure with the 2m elements. I was able to tune my antenna to a SWR of less than 1.2:1 across both bands.

Now that you've got the elements cut to the proper length, go ahead and tape the ends of the elements to the dowel, cut off the excess portion of the dowel from both ends of the dowel and glue the 1/2" pvc cover over the dowel. Also glue the end caps on the cover. It sould look like the below picture at this point:

IMG_20120930_180409.jpg

The next step is to build the rf choke. It consists of 7 or 8 turns of coax around the support pipe. Cut a 2' long piece of 3/4" pvc pipe and drill 2 holes through one side of the pipe. The first hole goes about 1.5" from the end and the second hole goes 3.5" from the end.

Start by pulling the coax through the end of the pipe that is closest to the first hole and out the hole from the inside. Takeup all the slack so there is none left between the antenna and the 3/4" pipe. Next, wrap the coax around the 3/4" pipe tightly as many times as necessary to take up all the space between the 2 holes and then route it back into the pipe through the second hole. When you are done, it should look like the picture below.

IMG_20121012_133043.jpg

Before you glue the 3/4" pipe into the tee, you'll want to decide if you'll be mounting the radiator horizontally (ssb dx use) or vertically (fm repeater use). Make sure that the holes in the 3/4" pipe are pointed down when you glue the pipe in place to prevent rain from entering the antenna.

I attached a 3/4" elbow to the end of my pipe and attached the remaining 3/4" pipe to use as a vertical support Which i attached to a downspout.you can see the semi-final location of my antenna below.

IMG_20121010_205941.jpg

A2m-70cmdipoleantennafor6bucks (last edited 2012-10-15 16:58:31 by 216)