Impedance Bridges for the Megacycle Range

1000 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1 9 5 2 individual transmission characteristics will produce cumulative errors, making it necessary to maintain close control over the manufacture and adjustment of all of these amplifiers and associated networks. This calls for networks of highly refined design and requires ancillary measurement facilities of greater precision than heretofore available at these higher frequencies. The design of transmission networks to meet exacting requirements is a subtle art, embracing on the one hand the use of complex mathematical manipulation to produce theoretical networks having the desired loss and phase characteristics, and requiring, on the other hand, a down-to-earth knowledge of the properties of the actual components used including parasitic effects and interaction of the various elements when assembled into a network. To furnish this knowledge, to measure the component resistors, capacitors, inductors and transformers which are the building blocks of the networks, to evaluate the ever-present parasitic effects, to determine simplified circuit equivalents of the more complex components such as transformers, and to answer other questions too numerous to mention, measurements of impedance parameters - precise measurements - are required. For measuring impedance and admittance parameters, that is R,, L, C and G, suitable ac bridges, ordinarily simply designated as impedance bridges, have long held a high place in the Bell System because of their inherent reliability and precision, and their ability to cover a wide range of values.