 Additionally , the sets demonstrated a serious problem with ground reflections . The broadcast antenna sent out the pulse over a very wide area covering the entire forward side of the aircraft . This meant that some of the broadcast energy struck the ground and reflected back to the receiver . The result was a solid line across the display at a distance equal to the aircraft 's altitude , beyond which nothing could be seen . This was fine when the aircraft was flying at 15 @,@ 000 feet ( 4 @.@ 6 km ) or more and the ground return was at about the maximum useful range , but meant that interceptions at lower altitudes offered increasingly shorter range . 
