PFB's Blog

These photos detail the process of assembling your own 9:1 magnetic UnUn / Balun for feeding an Amateur Radio station antenna. This is based on prior work done by a UK Ham M0UKD and you can view his original work at http://m0ukd.com/homebrew/baluns-and-ununs/91-magnetic-longwire-balun-unun/

I followed his example but adapted to materials I had on hand for the project. M0UKD selected a single T130-2 Iron Powder Core toroid and I used a stack of three FT114-43 toroids. Aside from that difference the rest is very similar.

Looking closely at the photos, you should be able to understand visually what the other Ham describes.

Beginning:

You make 9 complete passes. Take care not to cross the wires as you wind them. make sure you have started with enough that is not wound in order to make connections shown later in the process.

Next step:

After you have finished winding, and inspecting your work for errors you will make the first connection with the Black lead from the LEFT side to the RED lead from the right side. Trim to a manageable size, solder together and cover with shrink tubing.

Next step:

The next connection is made with the YELLOW lead from the LEFT side and the BLACK lead from the RIGHT side. Twist the leads together, trim to equal length as shown in the final photo. This lead-pair will be soldered to the HOT (center) connection of your coaxial cable connector.

Next step:

The next connection starts on one side at the back of the coaxial connector you selected. That lead soldered to the coaxial connector is joined with the YELLOW lead from the RIGHT side to become the connection to negative side of a dipole or to the grounding stake if the antenna your using is a random length end-fed rather than a dipole configuration.

As you can also see, the RED lead on the LEFT side is the HOT (positive) side of your dipole, or the HOT terminal to feed a random length end-fed antenna.

The final assembly looks like this:

In the next installment, once I return from a hardware store, I'll show how you can use a CANTEX electrical box to make a fully weather tight enclosure suitable for any number of situations.
This device should be able to comfortably handle up to about 150 watts from your HF transceiver. I've used similar designs with good results from 160 meters up through six meters with good results.