Linear theory of bridge and ring modulator circuits

An approximate theory is developed which permits the calculation of the matching impedances and insertion losses for bridge and ring modulators used in single-sideband telegraphy. It is assumed that the rectifier impedances change abruptly at each half-cycle from one pure resistance to another, the one being very small and the other very large. The matching impedances and losses are derived for bridge rectifiers terminated in two constant resistances, in two filters, in one resistance and one filter, and with an input-leak blocking circuit. A corresponding theory is developed for ring modulators working between constant resistances or filters. Experimental results are quoted for bridge modulators terminated in various ways. In order to test the validity of the resistive theory the effective resistance of the rectifiers was varied by the use of resistors in series and shunt. A circuit is described which compensates for the self-capacitance of the Cu2O rectifiers used. The measured performance of the modulators was in agreement with the simple theory proposed.