LA6NCA RADIO

BALUN



I have designed a controllable balun with three different output impedances.
I can select output impedance with two switches.
The output impedance is 22 ohms, 50 ohm and 112 ohm.
The output is balanced.r.




The balun is mounted in a shielded metal box.



The balun has two ferrite cores.
The first converts the signal from unbalanced signal to balanced signal.
The other is a voltage transformer with three different impedances out.
The output impedance is selected with two relays.

The cores are from Eidolon Norway.
Ni-Zn Ferrite 60mm (43), No.: 50219
http://www.eidolon.no/






I have installed a switch SW3 on the center tap of the transformer.





Here are the three switches that select the impedance and grounding.



To the left is the core that converts the signal to balanced.
Each of the windings is 10 turn.
The second core functions as a transformer that transforms the signal either up or down.
The midpoint of the transformer is grounded so that we can get a good balanced signal out.




Common mode rejection measurement.
I transmit the same signal at both terminals on the ballanced port.
Rx is connected to the unbalanced port.
Measure from 1 to 30 MHz.
Very good result. -45dB at 14 MHz.





Measurement of signal loss 1-30 MHz.
The loss is only 0.23 dB at 14 MHz.
Z in and Z out is 50 ohm

I have tested with 400 watts continuous carrier for 5 minutes.
The output was set to 112 ohms.
None of the cores was heat.

 




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