In the early days of radio communications, receivers produced by Telefunken, Berlin were mainly procured for the Swiss Armed Forces. With the advent of World War II, more Swiss-made equipment was introduced, such as superhet receivers from Autophon and Zellweger.

Surveillance receivers were acquired in larger numbers, and high-quality communications receivers were purchased in small numbers for interception services and radio surveillance.

In the early days, receivers were designated by an abbreviation Exx, E standing for receiver and the number for the year of introduction.

In 1951, a new nomenclature was introduced in the Swiss Army. Receivers were henceforth given the designation E-6xx, and the devices were numbered consecutively according to chronological order. The receivers still in service received a new designation according to the E-6xx nomenclature in addition to the old one.