Design of High Reliability Inductor for 1.5MHz LC Tuning Circuit and Substantiation of Aging Characteristics for 20Years

Abstract

The requirements for the LC tuning circuit of digital communication equipments, the authors started developing in 1963, were so tight that a resonant frequency stability, Δf/f₀=±0.274% (1.4 to 9.2V at -30 to 65°C for 20years) was more tight by one order of magnitude than that of conventional analogue ones. To satisfy these requirements, we studied inductors and revealed factors of their characteristics changes.
First, a ferrite pot core was selected because of its stable characteristics achieved by those days' rapid progress using study results of disaccommodation and so on in the ferrite field. The effective permeability was hold down to 10 to improve the stability. The core size was studied using Mn-Zn and Ni-Zn that could be available in the operating frequency. A 18/14-10 Ni-Zn ferrite pot core was revealed to be most suitable one including Q-characteristics. Aging characteristics was found to satisfy the requirement ΔL/L=-0.05±0.14% from 20-year measurement. This result verifies that 20-year aging characteristics of inductors can be preestimated with high accuracy from short-term data.