In extending the single frequency network (SFN), it is inevitable that the newly added broadcasting stations are established while the existing broadcasting stations are being operated. To identify the SFN signal overlapped area before and after the construction and to check whether the newly added transmitter signals are stably inter-operable to those of the existing transmitters without self-interference, the measurement vehicle should be fixed at a certain measurement point and the transmitter must be turned on and off up-to-date. Hence, as the number of fixed measurement points increases, the transmitters will be exposed to severe stress. Additionally, because the fixed measurement takes a long time to collect enough volume of data, it is not practical to use the old technology as it is. In this study, we propose a novel method to collect the field test data by mobile measurement under the fixed transmitter condition, i.e., turned on or off. Then, the difference between the two results is calculated using data processed by spatial interpolation to determine the SFN signal overlapped area quickly. After applying this to field test data, it is confirmed that coverage of each transmission site obtained by the proposed method is almost identical to that of the coverage prediction and planning software.