Low power Guanella 1:1 balun with low Insertion VSWR using a Fair-rite 2×2631540002 – measurement of Zcm

Low power Guanella 1:1 balun with low Insertion VSWR using a pair of Fair-rite 2631540002 suppression sleeves – design workup presented a desk design of a low power balun. This article presents measurement of common mode impedance Zcm of a prototype using a nanoVNA.

Above is the prototype 2631540002×2 wound with 3.5t of RG316.

Above is the plot of R and X components of Zcm from 1-30MHz. Self resonant frequency SRF is 5.4MHz.

|Zcm| is very high from 2-14.5MHz and high from 1-26MHz, and this should make an effective choke for most reasonable scenarios.

Having measured the SRF, we can calibrate the predictive model.

Above, the calibrated model is quite close in form to the measured, allowing for the rather wide tolerance of ferrite.

A follow up article will report thermal tests on the prototype balun.

References