From Transmission Line Transformers, Fourth Edition

Sec 11.1: Introduction

In Chapter 2 it was shown that the role of a transmission line transformer core is to enhance the choking action of the coiled windings to better isolate the input from the output circuit. Even though calculations were made for only the low-frequency performance of these transformers, experimental results demonstrated that the core influenced most of the operating region (see Sec 3.4).

The analysis for toroidal cores confirms that the low-frequency response is directly related to the permeability of the core material. With higher permeabilities, fewer turns are required, allowing for higher-frequency operation. It was also shown that rods, although not yielding the high reactance of the toroids, exhibit good low-frequency response and can be used in many applications. At low frequencies, the rod was found to be relatively insensitive to the permeability of the rod material because of the high reluctance of the air path around the core.

Accurate loss measurements have shown that only a limited number of ferrite materials are useful in power applications, where high efficiency is an important consideration. This chapter describes transmission line transformers that use nickel-zinc ferrite cores with permeabilities in the moderately low range of approximately 50 to 300, to yield efficiencies in excess of 98%. No conventional transformer can approach this performance. The losses are not a function of current as in the conventional transformer, but are, in most cases, related to the impedance levels at which the transformers are operated. This suggests a dielectric loss, rather than...

Products & Services
Ferrite Ceramics and Ferromagnetic Materials
Ferrite ceramics and ferromagnetic materials have dielectric and magnetic properties that are suitable for RF and microwave applications. They provide high electrical resistivity and low magnetic losses.
Ferrite Beads
Ferrite beads are used to suppress unwanted signals that can interfere with electrical devices such as DC supplies, transmission lines and cables. They provide attenuation of selected frequency bands.
Magnetic Cores
Magnetic cores are doughnut-shaped magnetic materials that are used with inductors, transformers and electromagnets. They are also used as computer memory elements.
Inductors, Coils, and Chokes
Inductors coils and chokes are passive components that are designed to resist changes in current and store energy in the form of a magnetic field. 
Single Phase Transformers
Single-phase transformers output single-phase AC power, typically while stepping-up or stepping-down the voltage between two circuits.

Topics of Interest

Sec 12.1: Introduction This chapter is directed to the person who does not have access to sophisticated test equipment and must rely on simple equipment which can be constructed from readily...

Sec 4.1: Introduction More recent experiments by the author (since the publication of the first edition of this book) revealed some interesting results concerning low-impedance applications. Foremost...

Sec 17.1: Introduction Two common uses of transformers are in power combiners/splitters and diode double-balanced mixers. Because these circuits typically use transformers with bifilar or trifilar...

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...

Sec 9.1: Introduction The balun ( balanced-to- unbalanced) transformer is a subset of the general class known as transmission line transformers. This class differs greatly from the conventional class...