It was my understanding that they converted the GWEN (Ground Wave Emergency Network) system over to create the Differential GPS signal. Those frequencies were in the 285-325 kHz LF band. Perhaps they have additional ones in the MF bands?
For those who are not familiar with GWEN, this was a hardened system that provided command and control of military assets in the case of nuclear war wiping out ionospheric communication, including NVIS, but would still allow for ground wave. By using lower frequencies, the ground wave was enhanced although it does require fairly good vertical antennas. Back in the 1990's I used to copy the experimental GWEN signals far beyond ground wave at night. 73, Rick, KV9U expeditionradio wrote: > Is it a DGPS signal? > > Bonnie > > >
