A part of present investigation has already been reported in this journal. The present report is concerned with the results of subsequent detailed research. We measured the frequency characteristics of the field winding over the frequency range of 50Hz to 800MHz by a network analyzer, a spectrum analyzer and a vector impedance meter to clarify the effect of conducted EMI (electromagnetic interference) of the field winding. The result may be summarized as follows : 1) the frequency characteristics of the field winding have parallel resonance at about IMHz, and many resonant phenomena above 100MHz, 2) the insertion loss characteristics of the field winding is equivalent to the characteristic of the composite filters which are composed of band-elimination filter (B. E. F) and low-pass filter (L. P. F), 3) at frequency below 100MHz, the equivalent circuit of the field winding is expressed by L-C parallel circuit, 4) the factor influencing the high frequency characteristics of the field winding is stray capacitance between the layers of the windings (at frequency below 100MHz) and interaction between the field winding and its surrounding condition (at frequency above 100MHz), 5) the noise current which passing the field winding is decreased largely at frequencies near parallel resonance of the equivalent circuit. From these results, it was proved that the conducted EMI of the commutator motor is influenced by the insertion loss characteristics of the field winding.

A part of present investigation has already been reported in this journal. The present report is concerned with the results of subsequent detailed research. We measured the frequency characteristics of the field winding over the frequency range of 50Hz to 800MHz by a network analyzer, a spectrum analyzer and a vector impedance meter to clarify the effect of conducted EMI (electromagnetic interference) of the field winding. The result may be summarized as follows : 1) the frequency characteristics of the field winding have parallel resonance at about IMHz, and many resonant phenomena above 100MHz, 2) the insertion loss characteristics of the field winding is equivalent to the characteristic of the composite filters which are composed of band-elimination filter (B. E. F) and low-pass filter (L. P. F), 3) at frequency below 100MHz, the equivalent circuit of the field winding is expressed by L-C parallel circuit, 4) the factor influencing the high frequency characteristics of the field winding is stray capacitance between the layers of the windings (at frequency below 100MHz) and interaction between the field winding and its surrounding condition (at frequency above 100MHz), 5) the noise current which passing the field winding is decreased largely at frequencies near parallel resonance of the equivalent circuit. From these results, it was proved that the conducted EMI of the commutator motor is influenced by the insertion loss characteristics of the field winding.