Except for the K and R Models, thermistor D (mounted inside the
waveguide) is protected against air currents, dirt, and mechanical damage by
two layers of polyfoam plastic.
Polyfoam is soluable in most volatile
etc., so great care should be used if one of these is used to clean the flange
or inner surfaces of the waveguide. Use the plastic flange cover to protect
the mount from direct and mechanical damage whenever it is not in use.
burn, dents or dirt on the flange or waveguide surfaces will increase the SWR.
This is particularly important in the case of the K486A and R486A, which do not
have the polyfoam plastic protection.