The M219 filter converts most thumpers into an efficient fault prelocating system, when used in conjunction with a TDR in the Arc Reflection Mode (ARM®). The ARM® method is a fast way to prelocate faults, and will reduce the time to pinpoint the fault and minimize the risk of additional damage to the cable. The use of a TDR in conjunction with a thumper requires the presence of a filter. It protects the TDR from the high voltage of the thumper and allows it to work in synchronization with the thumper. The thumper creates an arc at the location of the high resistance fault, converting it to a lower resistance fault while the arc is active. The low resistance fault is detected by the TDR as a reflection and the distance to the fault can be determined.