LM, the V-Force Radio Altimeter, a Mk 5 IIRC, went to 5000 feet. The Radar Altimeter, the Mk 6, went to 60,000 feet. It was a bit shabby below 500 feet.
The pair gave interesting and conflicting readings. The Mk 5 used to echo off the ground, the Mk 6 off the top of the tree canopy. Not good with 250 ft tall trees in the jungle.