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Building and measuring ununs

Updated: Jul 8

Remark: all return loss measurements (SWR) are with a light inductive load (adjustable resistor). Real results are always better then stated here.




Used core: FT240-31 Amidon.


4 wires 6 turns each

1 wire 4 turns.


Adjustable resistor of 100 Ohm adjust for minimum SWR, disconnect the resistor and measure the value with a multi meter.


Measured value was exact 68 Ohm as calculated value.









Schematic diagram:



Primary (left):


4 coils with 6 turns = 24 turns.


Secundary (right):


4 coils with 6 turns and 1 coil with 4 turns = 28 turns.





Impedance primary (50 Ohm) is 24 x 24 = 576

Impedance secundary 28 x 28 = 784


Calculated impedance secundary = (50/567) x 784 = 68 Ohm.








Used core: FT240-31 Amidon.

5 wires 5 turns each.

Adjustable resistor of 100 Ohm adjust for minimum SWR, disconnect the resistor and measure the value with a multi meter.

Measured value was 76.8 Ohm calculated value is 78 Ohm.





Schematic diagram:



Primary (left):

4 coils with 5 turns = 20 turns.

Secundary (right):

5 coils with 5 turns = 25 turns.





Impedance primary (50 Ohm) is 20 x 20 = 400

Impedance secundary 25 x 25 = 625

Calculated impedance secundary = (50/400) x 625 = 78 Ohm.





Comparison 5 coils with 5 turns each (above) <==> 5 coils with 6 turns each (under).


Used core: FT240-31 Amidon.

5 wires 6 turns each.

Adjustable resistor of 100 Ohm adjust for minimum SWR, disconnect the resistor and measure the value with a multi meter.

Measured value was 78 Ohm calculated value is 78 Ohm.










Schematic diagram:



Primary (left):

4 coils with 6 turns = 24 turns.




Secundary (right):

5 coils with 6 turns = 30 turns.


Impedance primary (50 Ohm) is 24 x 24 = 576


Impedance secundary 30 x 30 = 900

Calculated impedance secundary = (50/576) x 900 = 78 Ohm.



5 coils with 4 turns each.




Used core: FT240-31 Amidon.

5 wires 4 turns each.

Adjustable resistor of 100 Ohm adjust for minimum SWR, disconnect the resistor and measure the value with a multi meter.

Measured value was 78 Ohm calculated value is 78 Ohm.





Schematic diagram:


Primary (left):

4 coils with 4 turns = 16 turns.

Secundary (right):

5 coils with 4 turns = 20 turns.


Impedance primary (50 Ohm) is 16 x 16 = 256

Impedance secundary 20 x 20 = 400

Calculated impedance secundary = (50/256) x 400 = 78 Ohm.




Insertion loss measurement.


The setup:


2 x unun, first from 50 ohm to 78 ohm, second from 78 ohm to 50 ohm.

The results:







I have used the device on 80 meter. Insertion loss for two devices = 0,092 dB.

Insertion loss = 0,092 / 2 = 0,046 dB.

This means a loss of 1,05 % (see conversion tables).

In practice, when you use 100 Watts, only 1 Watt is lost in our device.


From 50 to 75 ohm withh one coil.


One coil 10 turns is output.

Input is 8 turns.











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