TABLE OF CONTENTS As noted in Chapter 1, the basic building block for all transmission line transformers is the simple, coiled transmission line. Guanella used several lines connected in series-parallel combinations, yielding broadband transformers with impedance ratios of 1:n 2, where n, the number of bifilar windings, has values of 2, 3, 4 and so on. In order to obtain the maximum high-frequency responses, the characteristic impedance of the transmission lines was required to be R L / n, where R L is the high-impedance side of the transformer. Experiments by the author have shown this to be the case and that the high-frequency response then is largely determined by the interwinding capacitance between adjacent bifilar turns. As with the 1:1 balun, if the characteristic impedance is the optimum value and the parasitics are kept to a minimum. Guanella's transformers are quite frequency independent.
Ruthroff used a single basic building block for his 1:4 balun and unun (unbalanced-to-unbalanced) transformers. By connecting the bifilar windings in two different ways, each summing a direct voltage and a delayed voltage via the transmission line, he was able to obtain these two broadband transformers. In most cases these transformers are capable of handling the maximum power level specified for Amateur Radio use in the HF band and beyond. Because of the phase difference in Ruthroff's method of combining voltages, another factor came into the determination of the high-frequency response the length of the transmission line. In fact, at the frequency at which...
