modulating time markers

   I'm looking into a time marker modulated onto a rf carrier that is
simple and at the same time accurate. The marker on the low frequency
signal carrying the US time reference which is said to invert the carrier
to mark the time certainly sounds simple. The remarkable accuracy of the
RTK GPS devices, actual inches are claimed, suggests a very accurate
means of reading the time marker.
   Anyone know of a text that deals with such circuitry or perhaps a
schematic of a gps reciever with enough detail to show how it's done?

Hul