 The general concept pre @-@ dated the Mk . IV and was essentially a UK version of the German Lorenz beam system . Lorenz , or Standard Beam Approach as it was known in the UK , used a single transmitter located off the far end of the active runway that was alternately connected to one of two slightly directional antennas using a motorized switch . The antennas were aimed so they sent their signals to the left and right of the runway , but their signals overlapped down the centreline . The switch spent 0 @.@ 2 seconds connected to the left antenna ( as seen from the aircraft ) and then 1 second on the right . 
