The photograph above is a little bit further on in the build. The toggle-switch on
the side wall opposite the PA is a weather-proof design. The purpose of this switch
is to enable selection of either the built-in 40MHz reference or an external GPS-Locked
10MHz source. Note that the modules are actually mounted on an internal sub-chassis.
This method was chosen so as to keep to a minimum the number of holes in what is
essentially a weather-proof box. The sub-chassis is screwed (blind-tapped) down onto
four tapped ledges on the floor of the box.