On Thu, 2 Jun 2005 07:40:35 -0700, Eunometic wrote
(in article .com):

The limitation of the AM seeker lies in the performance of the AM
detection (here x-axis) circuits, as the average signal from the
detector becomes quite weak in one direction thus producing poor
tracking performance in this axis. A scheme to resolve this is what is
termed frequency modulation (FM), whereby the number of spokes varies
with the radial distance from the centre of the reticle.

What do you call the no spokes version where you need to know the angular
position of the reticle? Say, from a synchronous motor's phase. I tried to
make one for tracking stars once long ago with a PMT. I still want to make
one work.

-- Charlie Springer