Increase the polarity using any of the top 3 knobs so that the line is rotating around the circle. If the line goes all the way around and the signal strength stays at 0% the whole time, use the polarity filter button on the far left of the console. If it goes around again and stays at 0%, press that button one more time. When you see the signal strength increase, use the knobs to get the line as close as possible to the spot that says 100%.