4 serial LPF, so called RC-4 filter. A fast pulse is converted to a slow pulse. A fast pulse is not suitable for a long transmission line because of the capasity and the impedance of the line.(Those make low pass filter in the line.) The fast spectro scopy pulse is converted to a slow pulse befor putting-out the signal to the long transmissin line. (for example, in the case of radiation measurement)
