English: This image shows two sample displays from a typical radar or the WWII era. The top image shows a normal radar return, with the range extended to the right. The leftover signal from the transmitter on the left side blanks out any local signals, and in this example there are two strong returns from more distant aircraft. The lower image shows the same returns but with the addition of an IFF Mark III on the closer of the two aircraft. This signal is received separately from the radar return, amplified, inverted, and then mixed with the radar signal. The result is that the "blip" goes below zero for those aircraft displaying IFF.