A mircrowave antenna was placed on top of the bunker.
This was to be a tropospheric scatter, or "troposcatter" radio station.
Troposcatter transmissions were considered to be the most reliable and secure means of communication and the least susceptible to nuclear disturbances in the atmosphere.
They take advantage of the scattering effects caused by conditions in the lower level of earth's atmosphere, the troposphere. A narrow beam of low frequency microwave signals transmitted at high power and aimed at a chosen point on the temperature layer formed at about 10 miles altitude, where the troposphere and statosphere meet, will be refracted back to a chosen area on the earth or the ocean.