Home Brew 1:1 4:1 & 9:1 Baluns.

After searching the internet for hours trying to find information on how to select the right iron core for the job, I kept coming across the same problem. There is a lot information on how to wind the balun but not on how to select the right core. I then came across Peter Miles’ VK6YSF website (www.vk6ysf.com) with some information on 1:1, 4:1 & 9:1 baluns.

More information is available on Peter’s website but the basic designs are below.

1:1 Ruthroff voltage Unbalance to Balance.

Used to couple 50/75ohm transmission line to 50/75ohm centre feed dipole.

1:1 Balun
1:1 Balun

Circuit diagram of the 1:1 balun.

1:1 Balun
1:1 Balun

Winding diagram of the 1:1 balun.

4:1 Ruthroff voltage Unbalance to Balance.

Used to couple 50 transmission line to 200ohm off centre feed dipole.

4:1 Balun
4:1 Balun

Circuit diagram of the 4:1 balun.

4:1 Balun
4:1 Balun

Winding diagram of the 4:1 Balun.

9:1 Unun.

Used couple 50 transmission line to 450ohm end feed long wire.

9:1 unun
9:1 unun

Circuit diamgram of the 9:1 unun.

9:1 unun
9:1 unun

Winding diagram of the 9:1 unun.

Core Selection.

The number of winding is the same for the 1:1 & 4:1 balun.

TOROID NUMBER OF TURNS POWER RATING
T80-2

25

60 Watts
T106-2

16

100 Watts
T130-2

18

150 Watts
T157-2

16

250 Watts
T200-2

17

400 Watts
T200A-2

13

400 Watts
T400-2

14

1000 Watts

The 9:1 Unun uses the following:

T200-2

9

400 Watts
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