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Building and measuring baluns (Part I).

Updated: 3 days ago

The 1: 4 Guanella current Balun with FT240 - 31 core.

Material used: FT240-31 (outer diameter is 2.4 inch material = 31)

Just Google FT240-31 for all info. Warning: use Teflon insulated wire.

The "crossing": this is not necessary. This is for mechanical point of view, output is then 180° relative to the input. Beware of the right way of winding.


Connection of the coils:


Input = 50 Ohm side (left) the coils are switched in parallel. Black wire of the upper coil is connected to the black wire of the lower coil. Do the same white wire.


Output = 200 Ohm side (right) the coils are switched in series.

The white wire of the lower coil is connected to the black wire of the upper coil.


Two 100 Ohm resistors in series are connected to the output of the balun.

The cores are mounted above each other. This is easier to build the into a housing.













The 1: 4 Guanella current Balun with FT240 - 43 core.


Material used: FT240-43 (outer diameter is 2.4 inch material = 43)

The "crossing": this is not necessary. This is for mechanical point of view, output is then 180° relative to the input. Beware of the right way of winding.



Connection of the coils:


Input = 50 Ohm side (left) the coils are switched in parallel. Grren wire of the upper coil is connected to the green wire of the lower coil. Do the same red wire.


Output = 200 Ohm side (right) the coils are switched in series.

The white wire of the lower coil is connected to the black wire of the upper coil.


Two 100 Ohm resistors in series are connected to the output of the balun.

The cores are mounted above each other. This is easier to build the into a housing.











Insertion loss measurement:


Device under test is two times a 1:4 Guanella current balun with FT140-43 material. Baluns are connected with the high impedance site together.

In 50 Ohm ===> 200 Ohm connected with 200 Ohm===> 50 Ohm (see picture below).



The setup:


The results:




Divide the result by two, to see the loss value of one device.

0,20 dB means that you have a power loss of 4,7 %.

If you use this balun in a perfect swr situation, running 100 Watts, Approx. 5 Watts will be lost in our device.














Common mode rejection:


Common mode rejection should be >20 dB

The setup:

Every resistor is 22 Ohm


Insertion loss of the setup = -1,73 dB due to 22 Ohm in series (result 72 Ohm visual on the smith diagram.

Total setup:


@ 1,5 MHz Rejection is -21,7 dB + 1,73 dB measuring setup = 20 dB

Rejection is ok from 160 meter until 6 meter.

@ 30 MHZ the rejection = 35 dB!




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