Mark

So.... the aircraft is loaded and crew in cockpit. You're called out for a intermittently failing Left Radio Altimeter indication. Cockpit full of mechanics looking for some sort of deferral to move the aircraft.

Rainy as hell for 4 days straight. A visual on the transmit and receive antennas revealed droplets and a water sheen covering the whole face of both.

A rag..... a wipe of both..... problem solved.

The images below are not the problem ones, but it can bee seen that signal interference is possible.

Radio altimeters transmit from 4275MHz to 4325Mhz. Water will definitely cause issues at these higher frequencies.