A New Antenna!

As some may remember, my only antenna used to be a Radiowavz DX40. Unfortunately that came down last month. It was a great antenna and I wanted to put it back up, but the antenna hasn't fared too well with the bizarre weather in Massachusetts over the past year. The balun was rusting and the wire was snapped. It was time for something new. After researching some different designs to save money with a homebrew antenna, I found that a loop antenna could be made very inexpensively. I wanted to put up the biggest one possible in order to take advantage of the available space in the yard. I found that a 40m full-wave loop would fit well. I also found it to be incredibly simple to make and put up. Here's a quick list of what you'll need:

•  About 150 feet of wire. I used 17 gauge aluminum electric fence wire. If you go with that, DO NOT use steel wire, the impedance is 4x that of the aluminum. This stuff is really inexpensive. I purchased 250 feet for about $5. 
• Support rope. 200-300 feet, depending on your setup would be enough. I use UV-resistant high strength parachute cord. You can also use Dacron. 
• 4 dogbone insulators. These are pretty cheap, about $1-2 each at any ham supplier. 
• 4:1 balun 
• 1:1 isolation transformer.

You can also do this with ladder line and eliminate the transformer and the balun, but most new hams have coax, so I'll cater to that. The formula for wire length is 1005/frequency (in MHz). I used 7.2 MHz as a target. That comes out to about 139.5 feet. You don't need to be exact with this. Loops are very broad-banded and you'll be using a tuner anyways. With loops, you can tune the antenna using a tuner from 10m all the way up to the target frequency. So in reality, if you had a 160m target, you'd have an all-band antenna. Here's a sketch of my antenna and how it's configured.

   

The yellow square is the antenna, the green is the support rigging, the blue is the insulators, the white square is the balun, and the star is where the coax enters the shack. The isolation transformer is just outside the shack window. Here are a few helpful hints as you move through your project:

•  Symmetry is not critical.
• The isolation transformer will help because it keeps rf off the shield of the coax. Loops are more susceptible to this than a dipole as there is so much more area to collect static. 
• Height is not critical, but higher is better. Mine is about 20 feet up. 
• The balun can be placed ANYWHERE on the loop. 
• You don't necessarily have to hook it up to a meter or analyzer and tune it. Just do the measurements correctly and you'll be ok.

You'll be surprised by the performance of a loop. If you're used to a dipole, you'll be amazed when you can break pileups and get that far-off DX contact! If you have any questions, send me an email at kc1ajt@kc1ajt.com


Update 12/28/15: The loop came down last week as a result from sharing a support with a new antenna and putting too much weight on the 17 gauge wire. I made the decision to put the antenna back up in the same configuration, but with 14 gauge wire. This time, I planned ahead and purchased 1/4 mile of wire for any future projects. The thicker wire is a little harder to work with because it doesn't bend or stretch as much, but in the end it will be better in the end.