More Fun With Baluns

I’ve written about building baluns before. I’m still quite proud of myself that I was able to build and deploy a couple of nice 1:1 baluns.

Of course, the next challenge is the 4:1 balun. I even bought a couple of AB240-125 kits to build one. Since my 40m dipole came down in the ice storm we had here over the weekend, I couldn’t really get on the air, so I decided to try it tonight.

The book Building and Using Baluns and Ununs by Jerry Sevick, W2FMI, has a whole chapter on building 4:1 baluns. After reading through it, I decided to build the Ruthroff design. Here’s the schematic:

The book shows several different designs, but the one that caught my eye was the low-power version on page 24. What I liked about it was that it was built with hookup wire instead of magnet wire. Using some cheap hookup wire, I could play around without possibly ruining the magnet wire.

One problem with using hookup wire is that it’s not as ductile as the magnet wire. This means it has a tendency to want to unravel. I did finally manage to get ten turns around the core, though. Here’s what it looks like:

Next, I clipped a 220-ohm resistor across the input and connected the output to my antenna analyzer. Here’s what I measured:

MHZ	Z
1.9	57
3.7	58
7.1	59
10.1	58
14.2	56
21.2	53
28.2	53

Amazingly, the thing actually seems to work! Not only that, it’s relatively flat over the HF frequency range. The next step is to package it into a nice enclosure, then put it to work.

I think my next antenna project is going to be the Cobra Antenna. They use a 4:1 balun to get the impedance of the antenna into a range tuneable by a common antenna tuner. K1JEK sells the antenna for $90-100, but you can build the thing for about a quarter of the price. More on that this weekend.