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The use of a line output transformer core to make a balun.

Updated: Apr 25, 2022


Be careful when removing the core as it is very fragile!


10 windings were made both top and bottom.

They behave like 100 ohm transmission lines.

Input parallel = 50 Ohms.

Output series = 200 Ohms.




Due to the good low frequency behavior and the capacitive behavior at high frequencies, I have decided to reduce the number of windings from 10 to 7.


2 x 10 turns 2 MHz 2 x 7 turns 2 MHz

Return loss 2 x 7 turns

SWR 2 x 7 turns




Insertion loss measuments:

Left: LOT core Right: FT240-43


Detail:



Total loss worst case = 0.4 dB @ 30 MHz

If we assume that both devices represent the same loss:

1 device represent 0.2 dB @ 30 MHz = 4.5 % power loss.














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