An agile switched-load transmitter for a communications system for a power distribution network comprises a resonant transponder (T1) with a variable primary frequency. The transmitter significantly increases the bandwidth for communications, significantly lessens the effect of bandwidth noise, and greatly improves both the quality of communications and data throughput. Switches (S1, S2) selectively connect the transponder to the communications systems and control current flow through a resonant circuit of the unit, particularly the timing between charging and discharging of a capacitive component thereof. This allows the frequency of operation of the transmitter to be controlled so an inbound signal has a frequency within a range of selected frequencies, rather than a fixed frequency, and enables the transponder to deliver an output signal of relatively high power that propagates through the power distribution network with relatively little loss in signal strength.