SPEKTRA Volume 6 issue 3 contains 5 papers: 1) Spectroscopic and Radiative Properties Of SM³⁺ Doped Sodium-Lead-Zinc-Lithium-Borate Glasses; 2) Detection and Monitoring System on The Package Receiving Box; 3) Working Analysis of Space Time Trellis Code on Wifi Mimo(2x2) System OFDM; 4) The Relationship Between Time and Water Content of Fish Dried Using Solar Panel-Based Dryers; and 5) Linear Generator Prototype with Vertical Configuration of Sea Wave Power Plant.