This work is motivated by the measurement of electron dynamics during edge-localized modes (ELMs) which is observed as electron cyclotron emission (ECE) bursts at edge. Considering a small optical thickness for both background and energetic electrons at the edge, detailed physical design and analysis of the ECE spectrum have been done when energetic electrons are considered at edge as in this technical note. The assembly of a portable eight-channel heterodyne radiometer is based on the building-block idea to conveniently adjust radio frequency components to suit for tokamak toroidal fields. Tests were performed in the 2016 Fiscal Year Campaign of Experimental Advanced Superconducting Tokamak (EAST) for demonstrating the ability of the system. Specifically, the bursting ECE in combination with the calculated spectrums indicates that the energetic electrons survive in the pedestal region and shift outward during the growing phase of an ELM.