From a post to ALT.BOOKS.DAVID-WEBER dated September 20, 1998:

Grav pulse comm and the detection of hyper footprints

    The Manticoran FTL com and, for that matter, gravitic sensors in general, do not function solely in normal-space. Or, to put it more precisely, they do not detect solely n-space phenomena. The grav pulses of an FTL com, like an impeller wedge, distort local n-space. They also produce an echo in hyper-space--a sort of ripple or cascade effect--which is what the gravitics actually detect and measure. In theory, any gravity field--even that of an itty-bitty meteor--produces the same sort of ripple or cascade; in practice, only a very powerful gravity field produces on which present-generations gravitics can detect and/or measure. A hyper footprint, on the other hand, is detectable at far greater distances than any impeller wedge simply because the "ripple" a starship produces as it actually enters or leaves hyper is much more of a roaring cataract. The real trick for the FTL com was developing the ability to produce finely controlled pulses (ripples), and the RMN has been steadily improving that ability.