A Simple Ferrite rod 1:1 HF balun

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This was a follow-up from the earlier QRO balun I ran the same tests using an antenna analyser, based on W8JI’s basic balanced quality test for current baluns

I connected a MFJ-226 antenna analyser to the balun via 37cm of RG58C/U, and tested SWR with the other end open and shorted, with the analyser set to sweep between 1MHz and 30MHz. The open and shorted case were SWR > 10. From G8JNJ’s experiments this implies through loss is likely to be < 1dB.

Eight 100ohm 1/4 W resistors were used, made up as two lots of four in parallel, making two 25R resistors. These were then wired in series to the binding posts, making up a centre tapped 50 ohm load.

1-30MHz Sweep with the balun terminated in 50 ohm. The red marker line is confusing, the Y axis is log starting at SWR=1.0 on the bottom up to 10 at the top

A 10cm lead was taken to the input on the balun, and the other end shorted to A and B as per W8JI’s article.

input ground shorted to one side of the balanced end

input ground shorted to the other side of the balanced end

and for a sanity check the input ground was shorted to the centre tap, which was very similar to the above two traces.

This meets W8JI’s basic balanced quality test. The marker on the last two traces has been set to approximately 1:1.2. It looks like this balun would be good for up to 14MHz, although the type of ferrite rod (Rapid 88-3098)is only specified for use up to 2MHz.

Richard G7LEE