Detail of waveguide inside the indoor unit:

Sevillana de Electricidad was the first electricity company to use microwave links in its communications. It was necessary to connect the Borbolla Power Plant with the Santiponce Substation, where the regional electricity grid's switching center was located. Voice and data services were maintained for many years on the 7 GHz band with a capacity of 12 channels.

Brown Boveri HK 418973 / 18 dlm – (Brown Boveri is part of the current company ABB)

Below, details.