alt55 radar altimeter troubleshooting

RadAltMath

SEA Avionics Rad Alt, this may be for a RT-300
MKV EGPWS Interface Control Document
4.1.3.2.2
ALT 55 Radio Altimeter
Single or dual ALT 55 analog altimeter interfaces are supported. The signal format is as follows.
Scale: For Radio Altitude <= 500 feet:
Volts DC = (0.02 × Feet) + 0.4
Scale: For Radio Altitude > 500 feet:
Volts DC = 0.003(Feet – 500) + 10.4
Range: -20 to 2500 feet AGL
Valid range is > -12 feet AGL. If adjustable, the on ground voltage should be set to between +0.2 and +0.3 VDC.