We finally got through the narrow banding process with our GPS. We have a Hiper II system with both internal low power radios and an external 35 watt radio. When we received the system it was not narrow banding, but could be narrow banded with a software change. We completed the narrow banding this week. When we first got the system we were able to get a range of close to 9 miles with the 35 watt radio. Now that we have narrow banded that range appears to be the same. We shot the same point today and it still worked. You can tell it is at the fringe of radio range, but it also appeared to be at the fringe of the range before narrow banding. So at least from my tests, narrow banding didn't really seem to hurt the range or slow the system down.