Charts for Simplifying High-Impedance Measurements with the Radio-Frequency Bridge

The equal-arm capacitance bridge for making radio-frequency impedance measurements gives excellent results with very little labor, provided the magnitude of the unknown impedance is not too high. If the unknown is high, and if its components change rapidly with frequency, it is desirable from the standpoint of ease of balance and accuracy of determination to shunt the unknown at the bridge terminals with a high-quality fixed condenser of known capacitance. The difficulty with this so-called shunt-condenser method has been the tedious calculations necessary to convert bridge readings into resistance and reactance of the unknown. In this paper there are presented charts which allow this conversion to be made quickly and easily. This should make possible more extensive use of the shunt-condenser method, especially in the standard broadcast band where there is considerable need for this type of measurement. In an example on the use of the charts there is pointed out a further advantage of the shunt-condenser method, the possibility for interpolation between bridge readings in the case of impedances which change very rapidly with the frequency.