Differential flux leakage in a Guanella 1:1 balun – an experiment

The article reports a simple experiment on the balun described at Low power Guanella 1:1 tuner balun using a pair of Jaycar LF1260 suppression sleeves to assess the loss with near zero common mode current.

This test would not subject dielectrics to high electric field strength.

LF1260x2-01

The balun above had the two wires at one end connected together, and a current of 1.41A at 7MHz passed between the terminals of the device at the other end.

The device so configured looks like a s/c transmission line stub and we would expect that the input impedance would be a very small resistance and small inductive reactance.

Screenshot - 28_09_2015 , 11_25_19

Above is a calculation of the stub, input impedance is calculated as 0.27+j8.60Ω. At a current of 1.41A, the differential voltage at the input end of the transmission line is 12.1V.

With a measured input current of 1.41A, we would expect dissipation of 1.41^2*0.27=0.54W. Most of this loss is conductor loss, increasing the Dielectric loss tangent by a factor of 100 made an insignificant difference to the result.

 

vt_00074

Above is a thermograph of the device after 15min at 1.41A. Temperature has risen from 8.0° to 12.6°, a rise of 4.6°.

Previous measurements of this device suggested temperature rise of 10.4°/W, indicating 4.6/10.4=0.44W, fairly consistent with the estimated 0.54W based on the transmission line model.

Any loss due to differential magnetic or electric field fringing into the ferrite is so small as to not contribute significantly to the measured temperature rise.

Conclusions

Dissipation from the balun under conditions of high differential current and negligible common mode current yielded temperature rise that is consistent with the loss expected from the transmission line conductors alone.

Any loss due to differential magnetic or electric field fringing into the ferrite is so small as to not contribute significantly to the measured temperature rise.

References

 

Last update: 28th September, 2015, 11:26 AM