I loved my 900Mhz BRB GPS setup on sub-Mach flights. Worked great. Sometimes the rocket would descend behind a hill, but if I went to the last coordinates transmitted, the receiver would pick up transmitter again and I could walk right to the rocket. Its last flight was well over Mach (Rasaero predicted 1.7). The boost was perfect and I actually heard the apogee deployment (you can even here it on the video from the camcorder on the ground). But the last transmitted coordinate, which the receiver screen displayed just a few seconds after launch, was over a quarter mile away. Not likely. Never regained lock. Rocket is lost. I can understand temporary lock loss but if I had known Mach+ flights had the potential to loose lock permanently, I never would used it for those flights. Lesson learned I guess.