Disclosed is a withdrawable device of main circuit for a circuit breaker. When an event associated with loading of the second content set is detected, the second content set is parsed to identify at least one sub-set of the second content set. When the initial channel interferes with the radio channels used by other slave apparatuses or the frequency bands used by PCs, the radio channel overlapping those frequency bands is avoided, and the radio channel of the frequency band that is the second highest priority is selected. The digital multiplier circuit is supplied a digital multiplier signal descriptive of a system function composed of a constant term and a second harmonic of the carrier frequency offset from zero frequency.