The 136B-2 Noise Blanker was designed to operate with the KWM-2 and 2A in mobile applications. This device is installed internal to the KWM2/2A and remove spike noise that resulted from RF emissions typical to mobile operation. This unit acts as a small receiver that picks up the same noise as the receiver in mobile operation. The 136B-2 modifies the phase of the noise spike by 180 degrees and feeds the result into a analogue adder to be added to the received noise spike. According to theory because of the phase shift the adder result is zero (eliminates the noise). This is a very simplified dissertation on this unit's operation. The bottom line is the device is effective and justified the expense. In the Collins Collectors market this device sell for $400 (08/00). BTW if you by one make sure you get the control pot with the unit (not shown here). I learned the hard way.