The effort to discover the location of agency radio units is as old as they are. During World War II, the German Funkabwehr (the Radio Defence Corps) enjoyed the most success in this field. Among the most sophisticated products of its kind were the belt sighting devices made by Kapsch. Post-war Czechoslovakia did not want to be left behind, so the Military Technical Institute developed a portable sight with the code name “POSPISIL”. The miniature frame goniometer with a long range and sensitivity was designed for close range targeting. The goniometer was concealed in an ordinary briefcase and sighting was performed unobtrusively with miniature earphones. The PRZ 48 prototype was approved by the Technical Commission on 31 March 1948, shortly after the February coup. This also foreshadowed the use of the serial type RZ 301, a feared tool in the hands of the State Security (StB).