Greetings, please kindly send me the diagram and the formulas for “The Copper Cactus Antenna” in 146, 225, 435 and 462 MHz
Thanks TI2TID

I just found your website and your excellent articles on antennas. I just got my ham license, again!, after 35+ years. I am very interested in CW, antennas, dx, etc. I like things better when I can make them myself.
Your articles are very helpful to me. Thank you for all of your work.
If an antenna could transport me to Italy, I would have built it already! hahaha (Land of my parents.)
Hope to meet you on the air.

Ciao,
Bob KD8UFC

I have a facination for listening short wave radio.
Let me have your document of the Magnetic Loop Antenna.

Many Thanks,

*John Hyeon*

The construction of a balun to go from 50 to 300 ohms for frequencies between 3 and 30 MHz.

Constructing a balun is pretty easy. Here’s how to make a balun to turn a 50 ohms unbalanced to 300 ohms balanced. It’s done with two tubes of type 43 ferrite. The size of the tubes depends on the power you want to run. In this example, I’m using two Fair-Rite tubes, with an outside diameter of 19mm, an interior diameter of 10.5mm, and a length of 50mm. (Note for the metric impaired: That’s about 3/4 inch outside, 3/8 inch or so inside, and 2 inches long. I don’t think the precise dimensions are critical.)

This balun requires several coils, three in this case. To illustrate, see figure 2.

Start with 2.5 turns (shown in blue) from one of the 300 ohm terminals and connect the other end of that to the coax outer shield. This will be the common for the balun. Starting from the ground, wind 2.5 more turns (shown in green) and connect that to the other 300 ohm terminal. Also, wind two turns (shown in red) from the ground and connect that to the coax center conductor. (NOTE: The diagram shows all of the windings being wound in the same direction, which matches information about similar baluns that I’ve seen elsewhere.)

The wire diameter is chosen to fill the center of the ferrite tube.

Following the same principle, you can make other impedance transformations by using different numbers of windings, as shown in the table: (NOTE: I won’t reproduce the table, the first number is the unbalanced impedance, the second one is the balanced impedance, the third is the number of turns of blue winding, the number of turns of green winding, and the number of turns of red winding.)

On a dummy load with an SWR of less than 1.5:1, I measured a loss of 0.4 dB.

You can use any kind of wire, enamelled, house wiring, or flexible industrial cable.

Here’s an example of a balun for a Window antenna.

Thank you