In the very early years of military wireless communications in Switzerland, the receiving equipment usually was bought together with complete wireless stations from commercial companies; these receivers were known by their commercial designation.
A few years later, abbreviations for the different types of receiving equipment were in use, usually consisting of Exx and the two digits of the year of introduction.
In the year 1951, a new designation scheme was introduced for all military telecommunications equipment, a few older sets still in use even got renamed according to the new designation scheme.
Since then, all receivers carry a designation following the E-6xx and a two digit number in ascending order designation scheme.
As an example, the „All Wave Receiver Autophon“ introduced in the year 1939 initially carried the designation E39, under which it is still very popular among Swiss former signalmen. After 1951, this receiver got the designation E-600 according to the new designation scheme.
Not for all E-6xx designations, the receiver type is known today. In very few cases, a Exx-designation has been re-used for another set in later years. One of this very few examples ist the designation E-606, initially used for the american National Company's HRO, in 1965 a solid state portable radio developed by Biennophone got the same designation E-606 and still can be found today in surplus shops.