Negative Ground Supply - Tait TM81 Serie Guía Del Usario

If a non-standard installation method is used, care must be
taken that sufficient heat can be dissipated from the radio
heatsink fins and the bottom surface of the radio chassis.
For this to be achieved, there must be a gap of more than
10mm (3/8 inch) between the bottom surface of the radio
chassis and the mounting surface.

Negative ground supply

TM8100 radios are designed to operate only in a negative
ground system.
28 Installation warnings
10mm (3/8 inch)
mounting surface