 The trailing edge of the transmitter pulse was not perfectly sharp and caused the receiver signals to ring for a short time even if they were turned on after the pulse was ostensibly complete . This leftover signal caused a large permanent blip known as the transmitter break through which appeared at the short @-@ range end of the tubes ( left and bottom ) . A control known as the <unk> Bias allowed the exact timing of the receiver 's activation relative to the transmitter pulse to be adjusted , normally so the remains of the pulse were just visible . 
