drawn diagrammatically the reticle 24 center follows the dash arrow path 40 during one nutational cycle a point p on the reticle 24 will move from the point shown at the bottom of the full line reticle 24 at a time t 1 to a point shown on the dash reticle 24 at a time t 2 at time t 2 the position of the reticle 24 in the beam will have spokes oriented as shown by the dash spoke outlines in fig5 as is known in the art frequency modulation coding of the beam occurs because of the shape of the spoke images and the instantaneous velocity of the spoke image across a detector aperture in fig6 one spoke of the reticle 24 is shown if the instantaneous velocity at the center of the reticle 29 is straight down as indicated for example in fig5 then the instantaneous velocity of all points on the spoke image also will be straight down and with the same velocity amplitude consequently the receiver 9 of the missile 2 in the beam looking back at the encoder 14 will receive energy when a transparent spoke 39 of the reticle 24 passes through the beam and will not receive energy when an opaque spoke 38 of the reticle 24 passes.