"MRW" wrote
... Why did my signal level drop at 100 ft?
_____________

The number that TIREM calculates will depend among other things on the
vector sum of the direct and ground-reflected or diffracted rays for the
model conditions -- which are a function of ERP, antenna height, path
length, and the terrain profile along that radial. Probably the combination
of these at the 100 ft elevation of the transmit antenna was responsible for
the result you saw.

If you get a chance, check several other radials to see what happens.

RF