Building a 4:1 Balun

For some time now, after hearing about the wonders of a LOOP antenna. I decided to build one that I could erect easily in the available space that I have here. I decided on building one for 40 Meters. Theoretically, I would also be able to use it on other bands. So I read as much of the available information I could find on LOOP antennas.

With only one central point to hang wire antennas, I decided to make a delta loop hung and fed at the top ( support point ), let the wire hang down vertically from the center and tie it off as best I could. Next decision was how to match the loop's characteristic impedance of approximately 100 ~ 120 Ohms so I could use RG58 feedline going to the shack. The conventional method is to use a quarter wave transformer made from 75 ohm coax. However, I decided to use a 4:1 balun at the feedpoint. Baluns, coax, open wire line, and other items used by Amateurs to construct antennas are hard to come by locally. So building a 4:1 balun was the best option I had.

The wire used for winding the balun ( 14 Guage ) was scavanged from an old transformer.

I wound 10 bifilar turns of the 14 guage wire on a small piece of 1 inch O.D. PVC pipe. This was then enclosed in a small piece of 1 1/2 inch O.D. PVC pipe and end caps for weatherproofing. Two stainless steel eyebolts are used to attach the antenna wires and another to support the balun.

So here is the construction of the balun in pictures.




Schematic of 4:1 Voltage Balun.

1:- Balun just finished winding coils.

2:- Second view
Balun just finished winding coils.

3:- Terminals added
Coated with sealant.

4:- Second view
Terminals added.
Coated with sealant.

5:- Balun and PVC end cap with
hole for Coax fitting.

6:- End cap with hole for coax fitting.

7:- Balun with coax fitting soldered in place.

8:- Second view of Balun with Coax fitting.

9:- End cap fitted over Balun.

10:- Another view - End cap fitted over Balun. Note drain hole.

11:- Another view - End cap fitted over Balun.

12:- Completed Balun.


There you have it. The completed Balun.

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