But it takes time to get the intentionally-introduced jitter out
The "jitter" is atmosphere induced, not DoD induced.
Thus, you only find them in surveying gear that has very nice antennas and very pricey boxes to do the signal processing.
The surveying gear has a differential GPS receiver as part of the system in addition to the mobile antenna the surveyor uses. The ground station transmits a signal that lets a differential receiver know about the error currently in the signal. This is a more localized but more accurate system comparable to WAAS.
-j