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9 to 1 balun.
The completed balun core - wired.

This balun was made with single ferrite core, (Jaycar L01234) wired using single strand Cat 5 UTP wire. The winding ratio is 6 turns to 18 turns. 50 ohm primary is 3 x 6 turns, wired in parallel. The 450 ohm secondary is formed by winding 2 x 9 turns in series, (grounding the centre tap) giving 18 turns overall. This gives a truely balanced to unbalanced impedance transformer. The picture here shows the balun core ready for testing. The two single wires are the 450 ohm secondary. The others are the 50 ohm primary with the larger one being the common ground.
9 to 1 Balun
The schematic

9 to 1 Balun schematic
So, what does the balun impedance look like?

Here's the Smith chart showing the impedance from 1 to 50MHz. The marker is at 30MHz.
9 to 1 smith chart
and the return loss?

Here's the VSWR from 1 to 50MHz. The marker is at 30MHz. Yes - it is that flat!!!
9 to 1 vswr
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