The Sigma Portable was produced in 1935/1936 in Czechia.  It operates as a TRF (tuned radio frequency) with manual regenerative (feed-back) control.  It covers two wavebands (MW and LW; 1000-2000 and 200-600 m), operates on 120 and 220 V AC and employs three tubes: AF7 (RF), B443 (LF) and 1801 (rectifier).  

The wooden cabinet measures 27 x 19 x 16 cm (width x height x depth).