|I have designed a
controllable balun with three different output
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
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
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
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
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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