Testing A Guanella Balun

After almost two years of conversation about the Guanella balun at our weekly Southeast Kansas Amateur Radio Club coffee’s it was time to do some real tests on a Guanella balun.

Test Balun

A test Guanella balun was wound with an 8:16 turn ratio and a 10:20 turn ratio on a FT-240 type 61 ferrite core. I used some old ribbon cable for the 8:16 winding and twisted pair from the inside of CAT-5 for the 10:20 turn ratio.

Test Setup

The test setup used a signal generator feeding into the 50 ohm impedance side of the Guanella balun with a 220 ohm resistor on the high impedance output of the balun. The signal was probed with run of the mill 1x scope probes and the ground point was the shield of the input coax.


The 10 minuet balun worked from about 6 MHz up to above 30 MHz, which is to be expected for type 61 ferrite.  Below 6 MHz the it became very unbalanced. Here is a link to the informtion on the FT-230 type 61 ferrite core.

4:1 Guanella Balun FT-240 Type 61 Core

4:1 Guanella Balun FT-240 Type 61 Core

The moral of the story, hams will argue about anything, it’s best to let it simmer for a year or two before taking measurements! Hi Hi!