From Transmission Line Transformers, Fourth Edition

Sec 7.1: Introduction

Little information is available on the characterization and practical design of transmission line transformers with impedance ratios of less than 1:4. Investigations reported in the literature have only treated the bifilar winding and its application to obtain impedance ratios of 1:1, 1:4, 1:9 and 1:16. But many applications can be found for efficient, broadband transformers with impedance ratios of 1:1.5, 1:2 and 1:3. Some examples include the matching of 50- ? coaxial cable to: (A) vertical antennas, inverted Ls and slopers (all over good ground systems), (B) a junction point of two 50- ? coaxial cables, (C) 75- ? coaxial cable and (D) shunt-fed towers performing as vertical antennas.

Early work by the author has shown that the tapped-Ruthroff 1:4 transformer can yield low-impedance designs under certain conditions. Their designs and limitations are included in this chapter. More recent work by the author has shown that, by far, a better technique is to use higher-order windings with the Ruthroff "bootstrap" method. This technique leads to further interesting applications such as broadband, multi-match transformers and compound arrangements leading to a new class of baluns: baluns which are capable of matching 50- ? cable directly to the low-impedance, balanced inputs of Yagi antennas and to the higher-impedance, balanced inputs of quad antennas.

The operation of these single-core, higher-order (trifilar, quadrifilar, and so on) winding transformers can be explained, briefly, by the 1:2.25 unun shown in Fig 7-1. The high-frequency schematic of Fig 7-1A assumes that...

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Topics of Interest

Sec 8.1: Introduction Transmission line transformers exhibit exceptionally high efficiencies over considerable bandwidths. By connecting several transformers in series, they can provide practical...

Sec 5.1: Introduction Chapter 4 dealt with transformer parameters for working at low-impedance levels; transformers which are basically used to match the ubiquitous 50- ? cable to impedances...

Sec 9.5: Baluns for Yagi, Quad and Rhombic Antennas To date, the most popular balun for antenna use has been the 1:1 (50:50- ?, nominally) trifilar design by Ruthroff. It has been used successfully...

Sec 9.4: The 1:9 Balun When matching a 50- ? coax down to a balanced load of 5.56 ? or up to a balanced load of 450 ?, the Guanella balun is the transformer of choice. There is little doubt that his...

Sec 9.2: The 1:1 Balun The 1:1 balun is well known to radio amateurs and antenna professionals, since it is widely used to match coaxial cables to dipole antennas and to Yagi beams that incorporate...