 Due to the physical location of the transponder , on the ground , the receiver antenna with the best view of the transponder was the one mounted under the wing . The radar operator would normally pick up the signal on the lower side of the elevation display , even at very long distances . Since the signal from the beacon was quite powerful , the Mk . IV included a switch that set the timebase to 60 miles ( 97 km ) for long @-@ distance pickup . Once they approached the general area , the signal would be strong enough to begin to appear on the azimuth ( left @-@ right ) tube . 
