discone

Here are a couple of antenna videos that I ran across this weekend:

While this is an interesting demonstration, what’s not known is how unbalanced the dipole was to start out with. Theoretically, if the two legs of the dipole are perfectly balanced, the balun is unnecessary. Also, we see in the video a meter presumably showing some amount of current flowing on the outer side of the coax. How much radiation actually results from that current is unknown, however.

I’m not saying that it’s not a good idea to use a balun. Even if you cut the elements of a dipole to be exactly the same length, once you get it in the air, there will be some imbalance because the environment won’t be perfectly balanced. How much that imbalance affects the system depends on the particular installation. When you use a balun, you force the currents to be the same in each leg of the dipole, and the current on the outer shield will be zero.

I’m just saying that this video isn’t that conclusive. It is actually an example of how arguments like this get started in the first place. The problem is that even when we try to make measurements, like IZ2UUF has done, the results can be debated. It’s difficult to make these measurements, even with professional-grade test equipment and facilities.

So, armed with inconclusive evidence, hams fall back on their personal experience, and since these experiences can differ widely, opinions differ widely. The ham who has never used a balun with a dipole and gotten good results, with little or no feedline radiation because he or she has managed to get a “good enough” balance, will not see the need for the extra expense of a balun. On the other hand, the ham who really has needed a balun and used one to good effect will sing the praises of using one.

Build your own discone

I’m a big fan of building, not buying antennas. So, I was intrigued when I saw a Tweet from Stu, KB1HQS, about his DIY discone antenna. He built this antenna using stuff he had around his house, namely a baby carriage wheel and a tomato cage. Very cool!

If you want to design and build your own discone, there are lots of resources on the internet. A search for “discone antenna design” yielded dozens of references, including:

• White Paper – Discone Antenna Design
• Discone Antenna Calculator

Let me know if you’ve built your own discone or how it goes when you do roll your own.